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  • 1.
    Andersson, Mattias L
    et al.
    Lund University, Sweden .
    Melianas, Armantas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Infahasaeng, Yingyot
    Lund University, Sweden .
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Yartsev, Arkady
    Lund University, Sweden .
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Sundstrom, Villy
    Lund University, Sweden .
    Unified Study of Recombination in Polymer:Fullerene Solar Cells Using Transient Absorption and Charge-Extraction Measurements2013In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 12, p. 2069-2072Article in journal (Refereed)
    Abstract [en]

    Recombination in the well-performing bulk heterojunction solar cell blend between the conjugated polymer TQ-1 and the substituted fullerene PCBM has been investigated with pump-probe transient absorption and charge extraction of photo-generated carriers (photo-CELIV). Both methods are shown to generate identical and overlapping data under appropriate experimental conditions. The dominant type of recombination is bimolecular with a rate constant of 7 x 10(-12) cm(-3) s(-1). This recombination rate is shown to be fully consistent with solar cell performance. Deviations from an ideal bimolecular recombination process, in this material system only observable at high pump fluences, are explained with a time-dependent charge-carrier mobility, and the implications of such a behavior for device development are discussed.

  • 2.
    Bai, Sai
    et al.
    Zhejiang University, Peoples R China; Zhejiang University, Peoples R China.
    Jin, Yizheng
    Zhejiang University, Peoples R China; Zhejiang University, Peoples R China.
    Liang, Xiaoyong
    Zhejiang University, Peoples R China; Zhejiang University, Peoples R China.
    Ye, Zhizhen
    Zhejiang University, Peoples R China; Zhejiang University, Peoples R China.
    Wu, Zhongwei
    Soochow University, Peoples R China.
    Sun, Baoquan
    Soochow University, Peoples R China.
    Ma, Zaifei
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Wang, Jianpu
    Nanjing Technical University, Peoples R China.
    Wuerfel, Uli
    Fraunhofer Institute Solar Energy Syst ISE, Germany; University of Freiburg, Germany.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Ethanedithiol Treatment of Solution-Processed ZnO Thin Films: Controlling the Intragap States of Electron Transporting Interlayers for Efficient and Stable Inverted Organic Photovoltaics2015In: ADVANCED ENERGY MATERIALS, ISSN 1614-6832, Vol. 5, no 5, p. 1401606-Article in journal (Refereed)
    Abstract [en]

    The surface defects of solution-processed ZnO films lead to various intragap states. When the solution-processed ZnO films are used as electron transport interlayers (ETLs) in inverted organic solar cells, the intragap states act as interfacial recombination centers for photogenerated charges and thereby degrade the device performance. Here, a simple passivation method based on ethanedithiol (EDT) treatment is demonstrated, which effectively removes the surface defects of the ZnO nanocrystal films by forming zinc ethanedithiolates. The passivation by EDT treatment modulates the intragap states of the ZnO films and introduces a new intragap band. When the EDT-treated ZnO nanocrystal films are used as ETLs in inverted organic solar cells, both the power conversion efficiency and stability of the devices are improved. The control studies show that the solar cells with EDT-treated ZnO films exhibit reduced charge recombination rates and enhanced charge extraction properties. These features are consistent with the fact that the modulation of the intragap states results in reduction of interfacial recombination as well as the improved charge selectivity and electron transport properties of the ETLs. It is further demonstrated that the EDT treatment-based passivation method can be extended to ZnO films deposited from sol-gel precursors.

  • 3.
    Bergqvist, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Lindqvist, Camilla
    Chalmers, Sweden .
    Backe, Olof
    Chalmers, Sweden .
    Ma, Zaifei
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tress, Wolfgang
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Gustafsson, Stefan
    Chalmers, Sweden .
    Wang, Ergang
    Chalmers, Sweden .
    Olsson, Eva
    Chalmers, Sweden .
    Andersson, Mats R.
    Chalmers, Sweden .
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Müller, Christian
    Chalmers, Sweden .
    Sub-glass transition annealing enhances polymer solar cell performance2014In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 2, no 17, p. 6146-6152Article in journal (Refereed)
    Abstract [en]

    Thermal annealing of non-crystalline polymer: fullerene blends typically results in a drastic decrease in solar cell performance. In particular aggressive annealing above the glass transition temperature results in a detrimental coarsening of the blend nanostructure. We demonstrate that mild annealing below the glass transition temperature is a viable avenue to control the nanostructure of a non-crystalline thiophene-quinoxaline copolymer: fullerene blend. Direct imaging methods indicate that coarsening of the blend nanostructure can be avoided. However, a combination of absorption and luminescence spectroscopy reveals that local changes in the polymer conformation as well as limited fullerene aggregation are permitted to occur. As a result, we are able to optimise the solar cell performance evenly across different positions of the coated area, which is a necessary criterion for large-scale, high throughput production.

  • 4.
    Bergqvist, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Tress, Wolfgang
    Laboratory of Photonics and Interfaces, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland.
    Forchheimer, Daniel
    Nanostructure Physics, KTH Royal Institute of Technology, Stockholm, Sweden.
    Melianas, Armantas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Haviland, David
    Nanostructure Physics, KTH Royal Institute of Technology, Stockholm, Sweden.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    New method for lateral mapping of bimolecular recombination in thin film organic solar cells2016In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 24, no 8, p. 1096-1108Article in journal (Refereed)
    Abstract [en]

    The best organic solar cells are limited by bimolecular recombination. Tools to study these losses are available; however, they are only developed for small area (laboratory-scale) devices and are not yet available for large area (production-scale) devices. Here we introduce the Intermodulation Light Beam-Induced Current (IMLBIC) technique, which allows simultaneous spatial mapping of both the amount of extracted photocurrent and the bimolecular recombination over the active area of a solar cell. We utilize the second-order non-linear dependence on the illumination intensity as a signature for bimolecular recombination. Using two lasers modulated with different frequencies, we record the photocurrent response at each modulation frequency and the bimolecular recombination in the second-order intermodulation response at the sum and difference of the two frequencies. Drift-diffusion simulations predict a unique response for different recombination mechanisms. We successfully verify our approach by studying solar cells known to have mainly bimolecular recombination and thus propose this method as a viable tool for lateral detection and characterization of the dominant recombination mechanisms in organic solar cells. We expect that IMLBIC will be an important future tool for characterization and detection of recombination losses in large area organic solar cells.

  • 5.
    Camacho, Rafael
    et al.
    Lund University, Sweden.
    Meyer, Matthias
    Lund University, Sweden.
    Vandewal, Koen
    Technical University of Dresden, Germany.
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Scheblykin, Ivan G.
    Lund University, Sweden.
    Polarization Imaging of Emissive Charge Transfer States in Polymer/Fullerene Blends2014In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 26, no 23, p. 6695-6704Article in journal (Refereed)
    Abstract [en]

    Photoexcitation of conjugated polymerfullerene blends results in population of a local charge transfer (CT) state at the interface between the two materials. The competition between recombination and dissociation of this interfacial state limits the generation of fully separated free charges. Therefore, a detailed understanding of the CT states is critical for building a comprehensive picture of the organic solar cells operation. We applied a new fluorescence microscopy method called two-dimensional polarization imaging to gain insight into the orientation of the transition dipole moments of the CT states, and the associated excitation energy transfer processes in TQ1:PCBM blend films. The polymer phase was oriented mechanically to relate the polymer dipole moment orientation to that of the CT states. CT state formation was observed to be much faster than energy transfer in the polymer phase. However, after being formed an emissive CT state does not exchange excitation energy with other CT states, suggesting that they are spatially and/or energetically isolated. We found that the quantum yield of the CT emission is smaller for CT states spatially located in the highly oriented polymer domains, which is interpreted as the result of enhanced CT state dissociation in highly ordered structures.

  • 6.
    Infahsaeng, Yingyot
    et al.
    Thammasat University, Thailand; Lund University, Sweden.
    Danna, Daniele
    Lund University, Sweden.
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Pascher, Torbjorn
    Lund University, Sweden.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Sundstrom, Villy
    Lund University, Sweden.
    Yartsev, Arkady
    Lund University, Sweden.
    Transient photocurrent of bulk heterojunction solar cell characterized by ns-laser and sub-ms LED2015In: INTERNATIONAL CONFERENCE ON PHOTONICS SOLUTIONS 2015, SPIE-INT SOC OPTICAL ENGINEERING , 2015, Vol. 9659, no UNSP 96591CConference paper (Refereed)
    Abstract [en]

    We measure the transient photocurrent of APFO3:PCBM bulk heterojunction solar cells illuminated with ns-laser and sub-ms LED light sources. The ratio of the number of collective charges to the number of excited photon (external quantum efficiency, EQE) and the transient photocurrent fall times have been carried out with difference pulse durations and fluences. The EQEs characterized by ns-laser source are shown to obey the bimolecular recombination at high excitation fluences. The increasing of transient photocurrent fall times suggests that the fall times of free charge carriers are effected by deep trap density of state (DoS) and thus the free charge carriers have a sufficient time for bimolecular recombination at short circuit condition. At the same fluences, however, the EQEs characterized by sub-ms LED sources exhibit an excitation fluences independence of EQE. The transient photocurrent fall times with sub-ms LED sources are rather constant when the excitation fluences increases indicating that the deep trap DoS has less effect at short circuit condition for longer pulse duration.

  • 7.
    Ma, Zaifei
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Dang, Dongfeng
    Chalmers, Sweden Xiangtan University, Peoples R China .
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Gedefaw, Desta
    Chalmers, Sweden .
    Bergqvist, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Zhu, Weiguo
    Xiangtan University, Peoples R China .
    Mammo, Wendimagegn
    University of Addis Ababa, Ethiopia .
    Andersson, Mats R.
    Chalmers, Sweden .
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Wang, Ergang
    Chalmers, Sweden .
    A Facile Method to Enhance Photovoltaic Performance of Benzodithiophene-Isoindigo Polymers by Inserting Bithiophene Spacer2014In: ADVANCED ENERGY MATERIALS, ISSN 1614-6832, Vol. 4, no 6Article in journal (Refereed)
    Abstract [en]

    A series of conjugated polymers containing benzodithiophene as donor and isoindigo as acceptor with no, one, two and three thiophene spacer groups is synthesized and characterized. The polymer with bithiophene as a spacer has a superior efficiency of 7.31% in solar cells. This demonstrates an important design strategy to produce polymers for high-performance solar cells by inserting thiophene spacer groups.

  • 8.
    Ma, Zaifei
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Sun, Wenjun
    Department of Chemical and Biological Engineering/Polymer Technology, Chalmers University of Technology, Göteborg, Sweden.
    Himmelberger, Scott
    Department of Material Science and Engineering, Stanford University, USA.
    Vandewal, Koen
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Bergqvist, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Salleo, Alberto
    Department of Material Science and Engineering, Stanford University, USA.
    Wenzel Andreasen, Jens
    Imaging and Structural Analysis Programme, Department of Energy Conversion and Storage, Technical University of Denmark, Denmark.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Andersson, Mats R
    Department of Chemical and Biological Engineering/Polymer Technology, Chalmers University of Technology, Sweden.
    Müller, Christian
    Department of Chemical and Biological Engineering/Polymer Technology, Chalmers University of Technology, Sweden.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Wang, Ergang
    Chalmers, Sweden .
    Structure-Property Relationships of Oligothiophene-Isoindigo Polymers for Efficient Bulk-Heterojunction Solar Cells2014In: energy and environmental science, ISSN 1754-5692, Vol. 17, no 1, p. 361-369Article in journal (Refereed)
    Abstract [en]

    A series of alternating oligothiophene (nT)-isoindigo (I) copolymers (PnTI) were synthesized to investigate the influence of the oligothiophene block length on the photovoltaic (PV) properties of PnTI:PCBM bulk-heterojunction blends. Our study indicates that the number of thiophene rings (n) in the repeating unit alters both, polymer crystallinity and polymer-fullerene interfacial energetics, which results in a decreasing open-circuit voltage (Voc) of the solar cells with increasing n. The short-circuit current density (Jsc) of P1TI:PCBM devices is limited by the absence of a significant driving force for electron transfer. Instead, blends based on P5TI and P6TI feature large polymer domains, which limit charge generation and thus Jsc. The best PV performance with a power conversion efficiency of up to 6.9% was achieved with devices based on P3TI, where a combination of favorable morphology and optimal interface energy level offset ensures efficient exciton separation and charge generation. The structure-property relationship demonstrated in this work is a valuable guideline for the design of high performance polymers with small energy losses during the charge generation process, allowing for the fabrication of efficient solar cells that combine a minimal loss in Voc with a high Jsc.

  • 9.
    Ma, Zaifei
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Wang, Ergang
    Chalmers, Sweden .
    Andersson, Mats R
    Chalmers, Sweden .
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Influences of Surface Roughness of ZnO Electron Transport Layer on the Photovoltaic Performance of Organic Inverted Solar Cells2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 46, p. 24462-24468Article in journal (Refereed)
    Abstract [en]

    Here, we demonstrate the correlation between the surface roughness of the ZnO interlayer used as an electron transporting interlayer (ETL) in organic inverted solar cells (ISCs) and the photovoltaic performance of the ISCs. Three different surfaces of the ZnO ETL are studied in ISCs with the polymer poly[2,3-bis-(3-octyloxyphenyl)-quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) mixed with [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) as the active layer. The results obtained from these ISCs show that power conversion efficiency increases from 2.7% to 3.9% when the root-mean-square roughness of the ZnO layer decreases from 48 to 1.9 nm. Moreover, it is found that the short-circuit current density is higher in the ISC based on the smoother ZnO interlayer, with a larger donor/acceptor (D/A) interfacial area in the active layer that facilitates exciton dissociation. The reduced effective interfacial area between the photoactive layer and the ZnO interlayer with decreased ZnO surface roughness leads to an observed improvement in both fill factor and open circuit voltage, which is ascribed to a reduced concentration of traps at the interface between the ZnO interlayer and the active layer.

  • 10.
    Murthy, D H K
    et al.
    Delft University of Technology, Netherlands .
    Melianas, Armantas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Juska, Gytis
    Vilnius University, Lithuania .
    Arlauskas, Kestutis
    Vilnius University, Lithuania .
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Siebbeles, Laurens D A
    Delft University of Technology, Netherlands .
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Savenije, Tom J
    Delft University of Technology, Netherlands .
    Origin of Reduced Bimolecular Recombination in Blends of Conjugated Polymers and Fullerenes2013In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 23, no 34, p. 4262-4268Article in journal (Refereed)
    Abstract [en]

    Bimolecular charge carrier recombination in blends of a conjugated copolymer based on a thiophene and quinoxaline (TQ1) with a fullerene derivative ((6,6)-phenyl-C-71-butyric acidmethyl ester, PC71BM) is studied by two complementary techniques. TRMC (time-resolved microwave conductance) monitors the conductance of photogenerated mobile charge carriers locally on a timescale of nanoseconds, while using photo-CELIV (charge extraction by linearly increasing voltage) charge carrier dynamics are monitored on a macroscopic scale and over tens of microseconds. Despite these significant differences in the length and time scales, both techniques show a reduced Langevin recombination with a prefactor close to 0.05. For TQ1:PC71BM blends, the value is independent of temperature. On comparing TRMC data with electroluminescence measurements it is concluded that the encounter complex and the charge transfer state have very similar energetic properties. The value for annealed poly(3-hexylthiophene) (P3HT):(6,6)-phenyl-C-61-butyric acid methyl ester (PC61BM) is approximately 10(-4), while for blend systems containing an amorphous polymer values are close to 1. These large differences can be related to the extent of charge delocalization of opposite charges in an encounter complex. Insight is provided into factors governing the bimolecular recombination process, which forms a major loss mechanism limiting the efficiency of polymer solar cells.

  • 11.
    Pranculis, Vytenis
    et al.
    Centre Phys Science and Technology, Lithuania .
    Infahsaeng, Yingyot
    Lund University, Sweden .
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Devizis, Andrius
    Centre Phys Science and Technology, Lithuania .
    Vithanage, Dimali A.
    Lund University, Sweden .
    Ponseca, Carlito S. Jr.
    Lund University, Sweden .
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Yartsev, Arkady P.
    Lund University, Sweden .
    Gulbinas, Vidmantas
    Centre Phys Science and Technology, Lithuania .
    Sundstrom, Villy
    Lund University, Sweden .
    Charge Carrier Generation and Transport in Different Stoichiometry APFO3:PC61BM Solar Cells2014In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 136, no 32, p. 11331-11338Article in journal (Refereed)
    Abstract [en]

    In this paper we studied carrier drift dynamics in APFO3:PC61BM solar cells of varied stoichiometry (2:1, 1:1, and 1:4 APFO3:PC61BM) over a wide time range, from subpicoseconds to microseconds with a combination of ultrafast optical electric field probing and conventional transient integrated photocurrent techniques. Carrier drift and extraction dynamics are strongly stoichiometry dependent: the speed of electron or hole drift increases with higher concentration of PC61BM or polymer, respectively. The electron extraction from a sample with 80% PC61BM takes place during hundreds of picoseconds, but slows down to sub-microseconds in a sample with 33% PC61BM. The hole extraction is less stoichiometry dependent: it varies form sub-nanoseconds to tens of nanoseconds when the PC61BM concentration changes from 33% to 80%. The electron extraction rate correlates with the conversion efficiency of solar cells, leading to the conclusion that fast electron motion is essential for efficient charge carrier separation preventing their geminate recombination.

  • 12.
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Chargeand Light Management in Organic Solar Cells2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Solar cells based on organic materials are extensively investigated both in academia and industry, owing to their potential of being inexpensive, lightweight, flexible and suitable for roll-to-roll production. Performance of organic solar cells has been rapidly improving, and the state of the art organic solar cells have an efficiency over 10%.

    This thesis aims to provide a comprehensive study of device engineering and device physics of organic solar cells. The ambition has been to investigate and optimize the conditions for light in-coupling and charge extraction in organic solar cells with alternative geometries. The ultimate goal is to propose methods that could potentially get the power conversion efficiency of organic solar cells with industrially compatible geometries over the current limit of 10%.

    To achieve such a goal, we employed a conjugated polymer as an interface modifier to improve the surface and electrical properties of substrate electrodes for solar cells with active layers based on blends containing conjugated polymers and fullerenes. A possibility of improving photovoltaic performance of easily fabricated reverse geometry solar cells (bottom metal cathode/active layer/top  transparent anode) has been demonstrated via this simple interface modification. Systematic investigations revealed that the enhanced device performance was not only related to the modified active layer/electrode interface but also changes in the bulk of the active layer. Consequently, the device performance of a reversed solar cell was found to be as good as that of a standard solar cell. The understanding of the effects of the interlayer modification on the performance of reversed solar cells, and the methodology provided in this thesis is a guideline for further studying and developing interface materials for highly efficient organic solar cells.

    An ITO electrode was further converted into a cathode by the polymer interlayer to construct semi-transparent solar cells with great potentials for building integrated photovoltaic applications. By stacking semi-transparent solar cells on top of each other, we showed that light can be more efficiently harvested compared to a conventional architecture solar cell. It has also been demonstrated that semitransparent solar cells combined with macroscopic light trapping elements can also be highly efficient.

    However, this thesis is not only about papers that I have published as a graduate student. The first five chapters have been included to provide background in the field of organic photovoltaics.

    List of papers
    1. Interlayer for Modified Cathode in Highly Efficient Inverted ITO-Free Organic Solar Cells
    Open this publication in new window or tab >>Interlayer for Modified Cathode in Highly Efficient Inverted ITO-Free Organic Solar Cells
    Show others...
    2012 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 24, no 4, p. 554-558Article in journal (Refereed) Published
    Abstract [en]

    Inverted polymer solar cells with a bottom metal cathode modified by a conjugated polymer interlayer show considerable improvement of photocurrent and fill factor, which is due to hole blocking at the interlayer, and a modified surface energy which affects the nanostructure in the TQ1/[70]PCBM blend.

    Place, publisher, year, edition, pages
    Wiley-Blackwell, 2012
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-74183 (URN)10.1002/adma.201104579 (DOI)
    Available from: 2012-01-20 Created: 2012-01-20 Last updated: 2017-12-08
    2. Universal modification of poor cathodes into good ones by a polymer interlayer for high performance reversed organic solar cells
    Open this publication in new window or tab >>Universal modification of poor cathodes into good ones by a polymer interlayer for high performance reversed organic solar cells
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    2014 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    In organic bulk-heterojunction solar cells, energy losses at the active layer/electrode interface are often observed. Modification of these interfaces with organic interlayers optimizes charge carrier injection and extraction and thus improves device performance. In this work, the effects of cathode modification by a conjugated polymer interlayer PFPA1 on the performance of reversed organic solar cells (substrate/cathode/active layer/transparent anode) based on different active material systems and different substrate electrodes are systematically investigated. A reduction of the work function irrespective of the substrate cathode used is observed upon the deposition of the PFPA1 interlayer; further related to an improved built-in electric field and open-circuit voltage. The amphiphilic character of the PFPA1 interlayer alters the surface energy of the substrate cathode, leading to the formation of a better active layer morphology aiding efficient exciton dissociation and photocurrent extraction in the modified solar cells. Hence, internal quantum efficiency is found significantly higher than that of their unmodified counterparts, while optically, the modified and unmodified solar cells are identical. Moreover, the deep HOMO of the PFPA1 interlayer improves the selectivity for all investigated substrate cathodes, thus enhancing the fill factor. We demonstrate a possibility of improving photovoltaic performance of reversed solar cells via a simple and universal interface modification and provide the basic guidelines for development and characterization of interface materials for organic solar cells in general.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-103928 (URN)
    Available from: 2014-02-03 Created: 2014-02-03 Last updated: 2018-09-01Bibliographically approved
    3. Semi-Transparent Tandem Organic Solar Cells with 90% Internal Quantum Efficiency
    Open this publication in new window or tab >>Semi-Transparent Tandem Organic Solar Cells with 90% Internal Quantum Efficiency
    Show others...
    2012 (English)In: ADVANCED ENERGY MATERIALS, ISSN 1614-6832, Vol. 2, no 12, p. 1467-1476Article in journal (Refereed) Published
    Abstract [en]

    Semi-transparent (ST) organic solar cells with potential application as power generating windows are studied. The main challenge is to find proper transparent electrodes with desired electrical and optical properties. In this work, this is addressed by employing an amphiphilic conjugated polymer PFPA-1 modified ITO coated glass substrate as the ohmic electron-collecting cathode and PEDOT:PSS PH1000 as the hole-collecting anode. For active layers based on different donor polymers, considerably lower reflection and parasitic absorption are found in the ST solar cells as compared to solar cells in the standard geometry with an ITO/PEDOT:PSS anode and a LiF/Al cathode. The ST solar cells have remarkably high internal quantum efficiency at short circuit condition (similar to 90%) and high transmittance (similar to 50%). Hence, efficient ST tandem solar cells with enhanced power conversion efficiency (PCE) compared to a single ST solar cell can be constructed by connecting the stacked two ST sub-cells in parallel. The total loss of photons by reflection, parasitic absorption and transmission in the ST tandem solar cell can be smaller than the loss in a standard solar cell based on the same active materials. We demonstrate this by stacking five separately prepared ST cells on top of each other, to obtain a higher photocurrent than in an optimized standard solar cell.

    Place, publisher, year, edition, pages
    Wiley-VCH Verlag Berlin, 2012
    Keywords
    polymer solar cells, semi-transparent solar cells, interface, conjugated polymers, tandem solar cells
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-86894 (URN)10.1002/aenm.201200204 (DOI)000312035800008 ()
    Note

    Funding Agencies|Swedish Energy Agency||Swedish Research Council||Advanced Functional Materials initiative at Linkoping University||Knut and Alice Wallenberg Foundation (KAW)||KAW||VINNOVA||

    Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2015-05-29
    4. Light trapping with total internal reflection and transparent electrodes in organic photovoltaic devices
    Open this publication in new window or tab >>Light trapping with total internal reflection and transparent electrodes in organic photovoltaic devices
    2012 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, no 16Article in journal (Refereed) Published
    Abstract [en]

    Herein, we demonstrate a method to build highly efficient light trapping structures for printed organic solar cells and modules, compatible with roll to roll manufacturing. Echelle grating structures in combination with semitransparent electrodes allow for efficient light trapping via means of total internal reflection. With this method, we demonstrate an increased cell photocurrent response up to 24%, compared to a standard cell configuration with a planar reflector. The demonstrated light trapping approach is expected to be even more useful for photovoltaic modules, where light hitting "dead areas" in between the sub-cells comprising the module will now be utilized.

    Place, publisher, year, edition, pages
    American Institute of Physics (AIP), 2012
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-87228 (URN)10.1063/1.4759125 (DOI)000310669300075 ()
    Available from: 2013-01-14 Created: 2013-01-14 Last updated: 2017-12-06
    5. Light Trapping with Dielectric Scatterers in Single- and Tandem-Junction Organic Solar Cells
    Open this publication in new window or tab >>Light Trapping with Dielectric Scatterers in Single- and Tandem-Junction Organic Solar Cells
    Show others...
    2013 (English)In: ADVANCED ENERGY MATERIALS, ISSN 1614-6832, Vol. 3, no 12, p. 1606-1613Article in journal (Refereed) Published
    Abstract [en]

    Efficient dielectric scatterers based on a mixture of TiO2 nanoparticles and polydimethylsiloxane are demonstratedfor light trapping in semitransparent organic solar cells. An improvement of 80% in the photocurrent of an optimized semitransparent solar cell is achieved with the dielectric scatterer with approximate to 100% diffuse reflectance for wavelengths larger than 400 nm. For a parallel tandem solar cell, the dielectric scatterer generates 20% more photocurrent compared with a silver mirror beneath the cell; for a series tandem solar cell, the dielectric scatterer can be used as a photocurrent balancer between the subcells with different photoabsorbing materials. The power conversion efficiency of the tandem cell in series configuration with balanced photocurrent in the subcells exceeds that of an optimized standard solar cell with a reflective electrode. The characteristics of polydimethylsiloxane, such as flexibility and the ability to stick conformably to surfaces, also remain in the dielectric scatterers, which makes the demonstrated light trapping configuration highly suitable for large scale module manufacturing of roll-to-roll printed organic single- or tandem-junction solar cells.

    Place, publisher, year, edition, pages
    Wiley-VCH Verlag, 2013
    Keywords
    light trapping; light scattering; organic solar cells; semitransparent solar cells; tandem solar cells
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-103295 (URN)10.1002/aenm.201300524 (DOI)000328337500012 ()
    Available from: 2014-01-17 Created: 2014-01-16 Last updated: 2014-02-03
    6. Light trapping in thin film organic solar cells
    Open this publication in new window or tab >>Light trapping in thin film organic solar cells
    2014 (English)In: Materials Today, ISSN 1369-7021, E-ISSN 1873-4103, Vol. 17, no 8, p. 389-396Article, review/survey (Refereed) Published
    Abstract [en]

    A major issue in organic solar cells is the poor mobility and recombination of the photogenerated charge carriers. The active layer has to be kept thin to facilitate charge transport and minimize recombination losses. However, optical losses due to inefficient light absorption in the thin active layers can be considerable in organic solar cells. Therefore, light trapping schemes are critically important for efficient organic solar cells. Traditional light trapping schemes for thick solar cells need to be modified for organic thin film solar cells in which coherent optics and wave effects play a significant role. In this review, we discuss the light trapping schemes for organic thin film solar cells, which includes geometric engineering of the structure of the solar cell at the micro and nanoscale, plasmonic structures, and more.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-103929 (URN)10.1016/j.mattod.2014.05.008 (DOI)000344209800018 ()
    Available from: 2014-02-03 Created: 2014-02-03 Last updated: 2017-12-06Bibliographically approved
  • 13.
    Tang, Zheng
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Andersson, Mattias
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    George, Zandra
    Chalmers University of Technology.
    Vandewal, Koen
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tvingstedt, Kristofer
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Heriksson, Patrik
    Chalmers University of Technology.
    Kroon, Renee
    Chalmers University of Technology.
    Andersson, Mats
    Chalmers University of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Interlayer for Modified Cathode in Highly Efficient Inverted ITO-Free Organic Solar Cells2012In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 24, no 4, p. 554-558Article in journal (Refereed)
    Abstract [en]

    Inverted polymer solar cells with a bottom metal cathode modified by a conjugated polymer interlayer show considerable improvement of photocurrent and fill factor, which is due to hole blocking at the interlayer, and a modified surface energy which affects the nanostructure in the TQ1/[70]PCBM blend.

  • 14.
    Tang, Zheng
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Elfwing, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Bergqvist, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tress, Wolfgang
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Light Trapping with Dielectric Scatterers in Single- and Tandem-Junction Organic Solar Cells2013In: ADVANCED ENERGY MATERIALS, ISSN 1614-6832, Vol. 3, no 12, p. 1606-1613Article in journal (Refereed)
    Abstract [en]

    Efficient dielectric scatterers based on a mixture of TiO2 nanoparticles and polydimethylsiloxane are demonstratedfor light trapping in semitransparent organic solar cells. An improvement of 80% in the photocurrent of an optimized semitransparent solar cell is achieved with the dielectric scatterer with approximate to 100% diffuse reflectance for wavelengths larger than 400 nm. For a parallel tandem solar cell, the dielectric scatterer generates 20% more photocurrent compared with a silver mirror beneath the cell; for a series tandem solar cell, the dielectric scatterer can be used as a photocurrent balancer between the subcells with different photoabsorbing materials. The power conversion efficiency of the tandem cell in series configuration with balanced photocurrent in the subcells exceeds that of an optimized standard solar cell with a reflective electrode. The characteristics of polydimethylsiloxane, such as flexibility and the ability to stick conformably to surfaces, also remain in the dielectric scatterers, which makes the demonstrated light trapping configuration highly suitable for large scale module manufacturing of roll-to-roll printed organic single- or tandem-junction solar cells.

  • 15.
    Tang, Zheng
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Elfwing, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Melianas, Armantas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Bergqvist, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Bao, Qinye
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Fully-solution-processed organic solar cells with a highly efficient paper-based light trapping element2015In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 48, p. 24289-24296Article in journal (Refereed)
    Abstract [en]

    We demonstrate the use of low cost paper as an efficient light-trapping element for thin film photovoltaics. We verify its use in fully-solution processed organic photovoltaic devices with the highest power conversion efficiency and the lowest internal electrical losses reported so far, the architecture of which - unlike most of the studied geometries to date - is suitable for upscaling, i.e. commercialization. The use of the paper-reflector enhances the external quantum efficiency (EQE) of the organic photovoltaic device by a factor of approximate to 1.5-2.5 over the solar spectrum, which rivals the light harvesting efficiency of a highly-reflective but also considerably more expensive silver mirror back-reflector. Moreover, by detailed theoretical and experimental analysis, we show that further improvements in the photovoltaic performance of organic solar cells employing PEDOT:PSS as both electrodes rely on the future development of high-conductivity and high-transmittance PEDOT:PSS. This is due optical losses in the PEDOT:PSS electrodes.

  • 16.
    Tang, Zheng
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    George, Zandra
    Chalmers, Sweden .
    Ma, Zaifei
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Bergqvist, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tvingstedt, Kristofer
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Vandewal, Koen
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Wang, Ergang
    Chalmers, Sweden .
    Andersson, Mattias
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Andersson, Mats R
    Chalmers, Sweden .
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Semi-Transparent Tandem Organic Solar Cells with 90% Internal Quantum Efficiency2012In: ADVANCED ENERGY MATERIALS, ISSN 1614-6832, Vol. 2, no 12, p. 1467-1476Article in journal (Refereed)
    Abstract [en]

    Semi-transparent (ST) organic solar cells with potential application as power generating windows are studied. The main challenge is to find proper transparent electrodes with desired electrical and optical properties. In this work, this is addressed by employing an amphiphilic conjugated polymer PFPA-1 modified ITO coated glass substrate as the ohmic electron-collecting cathode and PEDOT:PSS PH1000 as the hole-collecting anode. For active layers based on different donor polymers, considerably lower reflection and parasitic absorption are found in the ST solar cells as compared to solar cells in the standard geometry with an ITO/PEDOT:PSS anode and a LiF/Al cathode. The ST solar cells have remarkably high internal quantum efficiency at short circuit condition (similar to 90%) and high transmittance (similar to 50%). Hence, efficient ST tandem solar cells with enhanced power conversion efficiency (PCE) compared to a single ST solar cell can be constructed by connecting the stacked two ST sub-cells in parallel. The total loss of photons by reflection, parasitic absorption and transmission in the ST tandem solar cell can be smaller than the loss in a standard solar cell based on the same active materials. We demonstrate this by stacking five separately prepared ST cells on top of each other, to obtain a higher photocurrent than in an optimized standard solar cell.

  • 17.
    Tang, Zheng
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Liu, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Melianas, Armantas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Bergqvist, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tress, Wolfgang
    Ecole Polytech Federal Lausanne, Switzerland.
    Bao, Qinye
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Qian, Deping
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    A New Fullerene-Free Bulk-Heterojunction System for Efficient High-Voltage and High-Fill Factor Solution-Processed Organic Photovoltaics2015In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 27, no 11, p. 1900-+Article in journal (Refereed)
    Abstract [en]

    Small molecule donor/polymer acceptor bulk-heterojunction films with both compounds strongly absorbing have great potential for further enhancement of the performance of organic solar cells. By employing a newly synthesized small molecule donor with a commercially available polymer acceptor in a solution-processed fullerene-free system, a high power conversion efficiency of close to 4% is reported.

  • 18.
    Tang, Zheng
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tress, Wolfgang
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Bao, Qinye
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Jafari, Mohammad Javad
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, The Institute of Technology.
    Bergqvist, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Ederth, Thomas
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, The Institute of Technology.
    Andersson, Mats R.
    , Chalmers University of Technology, Göteborg, Sweden; University of South Australia, Australia.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Improving Cathodes with a Polymer Interlayer in Reversed Organic Solar Cells2014In: Advanced Energy Materials, ISSN 1614-6832, Vol. 4, no 15, article id 1400643Article in journal (Refereed)
    Abstract [en]

    The effects of cathode modification by a conjugated polymer interlayer PFPA1 on the performance of reversed organic solar cells (substrate/cathode/active layer/transparent anode) based on different active material systems and different substrate electrodes are systematically investigated. A reduction of the work function irrespective of the substrate cathode used is observed upon the deposition of the PFPA1 interlayer, which is further related to an improved built-in electric field and open-circuit voltage. The amphiphilic character of the PFPA1 interlayer alters the surface energy of the substrate cathode, leading to the formation of a better active layer morphology aiding efficient exciton dissociation and photocurrent extraction in the modified solar cells. Hence, internal quantum efficiency is found to be significantly higher than that of their unmodified counterparts, while optically, the modified and unmodified solar cells are identical. Moreover, the deep highest occupied molecular orbital (HOMO) of the PFPA1 interlayer improves the selectivity for all investigated substrate cathodes, thus enhancing the fill factor.

  • 19.
    Tang, Zheng
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tress, Wolfgang
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Bao, Qinye
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Jafari, Mohammad Javad
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering.
    Bergqvist, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Ederth, Thomas
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering.
    Andersson, Mats R.
    Polymer Technology, Department of Chemical and Biological Engineering, Chalmers University of Technology, Göteborg, Sweden.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Universal modification of poor cathodes into good ones by a polymer interlayer for high performance reversed organic solar cells2014Manuscript (preprint) (Other academic)
    Abstract [en]

    In organic bulk-heterojunction solar cells, energy losses at the active layer/electrode interface are often observed. Modification of these interfaces with organic interlayers optimizes charge carrier injection and extraction and thus improves device performance. In this work, the effects of cathode modification by a conjugated polymer interlayer PFPA1 on the performance of reversed organic solar cells (substrate/cathode/active layer/transparent anode) based on different active material systems and different substrate electrodes are systematically investigated. A reduction of the work function irrespective of the substrate cathode used is observed upon the deposition of the PFPA1 interlayer; further related to an improved built-in electric field and open-circuit voltage. The amphiphilic character of the PFPA1 interlayer alters the surface energy of the substrate cathode, leading to the formation of a better active layer morphology aiding efficient exciton dissociation and photocurrent extraction in the modified solar cells. Hence, internal quantum efficiency is found significantly higher than that of their unmodified counterparts, while optically, the modified and unmodified solar cells are identical. Moreover, the deep HOMO of the PFPA1 interlayer improves the selectivity for all investigated substrate cathodes, thus enhancing the fill factor. We demonstrate a possibility of improving photovoltaic performance of reversed solar cells via a simple and universal interface modification and provide the basic guidelines for development and characterization of interface materials for organic solar cells in general.

  • 20.
    Tang, Zheng
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tress, Wolfgang
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Light trapping in thin film organic solar cells2014In: Materials Today, ISSN 1369-7021, E-ISSN 1873-4103, Vol. 17, no 8, p. 389-396Article, review/survey (Refereed)
    Abstract [en]

    A major issue in organic solar cells is the poor mobility and recombination of the photogenerated charge carriers. The active layer has to be kept thin to facilitate charge transport and minimize recombination losses. However, optical losses due to inefficient light absorption in the thin active layers can be considerable in organic solar cells. Therefore, light trapping schemes are critically important for efficient organic solar cells. Traditional light trapping schemes for thick solar cells need to be modified for organic thin film solar cells in which coherent optics and wave effects play a significant role. In this review, we discuss the light trapping schemes for organic thin film solar cells, which includes geometric engineering of the structure of the solar cell at the micro and nanoscale, plasmonic structures, and more.

  • 21.
    Tvingstedt, Kristofer
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Light trapping with total internal reflection and transparent electrodes in organic photovoltaic devices2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, no 16Article in journal (Refereed)
    Abstract [en]

    Herein, we demonstrate a method to build highly efficient light trapping structures for printed organic solar cells and modules, compatible with roll to roll manufacturing. Echelle grating structures in combination with semitransparent electrodes allow for efficient light trapping via means of total internal reflection. With this method, we demonstrate an increased cell photocurrent response up to 24%, compared to a standard cell configuration with a planar reflector. The demonstrated light trapping approach is expected to be even more useful for photovoltaic modules, where light hitting "dead areas" in between the sub-cells comprising the module will now be utilized.

  • 22.
    Vandewal, Koen
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ma, Zaifei
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Bergqvist, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Wang, Ergang
    Chalmers, Sweden .
    Henriksson, Patrik
    Chalmers, Sweden .
    Tvingstedt, Kristofer
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Andersson, Mats R
    Chalmers, Sweden .
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Quantification of Quantum Efficiency and Energy Losses in Low Bandgap Polymer:Fullerene Solar Cells with High Open-Circuit Voltage2012In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 22, no 16, p. 3480-3490Article in journal (Refereed)
    Abstract [en]

    In organic solar cells based on polymer:fullerene blends, energy is lost due to electron transfer from polymer to fullerene. Minimizing the difference between the energy of the polymer exciton (ED*) and the energy of the charge transfer state (ECT) will optimize the open-circuit voltage (Voc). In this work, this energy loss ED*-ECT is measured directly via Fourier-transform photocurrent spectroscopy and electroluminescence measurements. Polymer:fullerene photovoltaic devices comprising two different isoindigo containing polymers: P3TI and PTI-1, are studied. Even though the chemical structures and the optical gaps of P3TI and PTI-1 are similar (1.4 eV1.5 eV), the optimized photovoltaic devices show large differences in Voc and internal quantum efficiency (IQE). For P3TI:PC71BM blends a ED*-ECT of similar to 0.1 eV, a Voc of 0.7 V and an IQE of 87% are found. For PTI-1:PC61BM blends an absence of sub-gap charge transfer absorption and emission bands is found, indicating almost no energy loss in the electron transfer step. Hence a higher Voc of 0.92 V, but low IQE of 45% is obtained. Morphological studies and field dependent photoluminescence quenching indicate that the lower IQE for the PTI-1 system is not due to a too coarse morphology, but is related to interfacial energetics. Losses between ECT and qVoc due to radiative and non-radiative recombination are quantified for both material systems, indicating that for the PTI-1:PC61BM material system, Voc can only be increased by decreasing the non-radiative recombination pathways. This work demonstrates the possibility of obtaining modestly high IQE values for material systems with a small energy offset (andlt;0.1 eV) and a high Voc.

  • 23.
    Xia, Yuxin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Jinan University, Peoples R China.
    Musumeci, Chiara
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Bergqvist, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ma, Wei
    Xi An Jiao Tong University, Peoples R China.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Bai, Sai
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Jin, Yizheng
    Zhejiang University, Peoples R China.
    Zhu, Chenhui
    University of Calif Berkeley, CA 94720 USA.
    Kroon, Renee
    Zhejiang University, Peoples R China.
    Wang, Cheng
    University of Calif Berkeley, CA 94720 USA.
    Andersson, Mats R.
    University of S Australia, Australia.
    Hou, Lintao
    Jinan University, Peoples R China.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Wang, Ergang
    Chalmers, Sweden.
    Inverted all-polymer solar cells based on a quinoxaline-thiophene/naphthalene-diimide polymer blend improved by annealing2016In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 4, no 10, p. 3835-3843Article in journal (Refereed)
    Abstract [en]

    We have investigated the effect of thermal annealing on the photovoltaic parameters of all-polymer solar cells based on a quinoxaline-thiophene donor polymer (TQ1) and a naphthalene diimide acceptor polymer (N2200). The annealed devices show a doubled power conversion efficiency compared to nonannealed devices, due to the higher short-circuit current (J(sc)) and fill factor (FF), but with a lower open circuit voltage (V-oc). On the basis of the morphology-mobility examination by several scanning force microscopy techniques, and by grazing-incidence wide-angle X-ray scattering, we conclude that better charge transport is achieved by higher order and better interconnected networks of the bulk heterojunction in the annealed active layers. The annealing improves charge transport and extends the conjugation length of the polymers, which do help in charge generation and meanwhile reduce recombination. Photoluminescence, electroluminescence, and light intensity dependence measurements reveal how this morphological change affects charge generation and recombination. As a result, the J(sc) and FF are significantly improved. However, the smaller band gap and the higher HOMO level of TQ1 upon annealing causes a lower V-oc. The blend of an amorphous polymer TQ1, and a semi-crystalline polymer N2200, can thus be modified by thermal annealing to double the power conversion efficiency.

  • 24.
    Zhen, Hongyu
    et al.
    Zhejiang Univ, Peoples R China.
    Li, Kan
    Zhejiang University, Peoples R China .
    Huang, Zhuoyin
    Zhejiang University, Peoples R China .
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Wu, Rengmao
    Zhejiang University, Peoples R China .
    Li, Guolong
    Zhejiang University, Peoples R China .
    Liu, Xu
    Zhejiang University, Peoples R China .
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Inverted indium-tin-oxide-free cone-shaped polymer solar cells for light trapping2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 21, p. 213901-Article in journal (Refereed)
    Abstract [en]

    Based on the flexibility of polymer film, cone-shaped polymer solar cells (PSCs) are fabricated and studied. Effective light trapping is achieved due to multi-absorption in all 360 degrees directions. Monte Carlo ray tracing is used to simulate the absorption of cone-shaped PSCs with two variables: wavelength and half cone angle. With an inverted indium-tin-oxide-free device structure, a 43% enhanced light utilization without loss of material utilization is realized in the cone-shaped PSCs with a half cone angle of 45 degrees, compared with the planar PSCs.

  • 25.
    Zhuang, Wenliu
    et al.
    Chalmers, Sweden .
    Zhen, Hongyu
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Kroon, Renee
    Chalmers, Sweden .
    Tang, Zheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Hellstrom, Stefan
    Chalmers, Sweden .
    Hou, Lintao
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Wang, Ergang
    Chalmers, Sweden .
    Gedefaw, Desta
    Chalmers, Sweden .
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Andersson, Mats R.
    Chalmers, Sweden .
    Molecular orbital energy level modulation through incorporation of selenium and fluorine into conjugated polymers for organic photovoltaic cells2013In: JOURNAL OF MATERIALS CHEMISTRY A, ISSN 2050-7488, Vol. 1, no 43, p. 13422-13425Article in journal (Refereed)
    Abstract [en]

    We demonstrated an effective chemical approach to modulate the energy levels of conjugated polymers by synergistically combining fluorine substitution and thiophene-selenophene exchange. Such modifications from TQ1 resulted in a significantly enhanced open-circuit voltage up to 1.0 V while retaining high photovoltaic performance.

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