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Tang, Zheng
Publications (10 of 25) Show all publications
Xia, Y., Musumeci, C., Bergqvist, J., Ma, W., Gao, F., Tang, Z., . . . Wang, E. (2016). Inverted all-polymer solar cells based on a quinoxaline-thiophene/naphthalene-diimide polymer blend improved by annealing. Journal of Materials Chemistry A, 4(10), 3835-3843
Open this publication in new window or tab >>Inverted all-polymer solar cells based on a quinoxaline-thiophene/naphthalene-diimide polymer blend improved by annealing
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2016 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 4, no 10, p. 3835-3843Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2016
National Category
Biological Sciences
Identifiers
urn:nbn:se:liu:diva-127066 (URN)10.1039/c6ta00531d (DOI)000371967000030 ()
Note

Funding Agencies|Swedish Energy Agency; Swedish Research council, NSFC [21504006, 21534003]; Knut and Alice Wallenberg Foundation through a Wallenberg scholar grant; China Scholarship Council (CSC); graduate student short-term abroad research project of Jinan University; program for the Excellent Doctoral Dissertations of Guangdong Province [ybzzxm201114]; U.S. Department of Energy [DE-AC02-05CH11231]

Available from: 2016-04-13 Created: 2016-04-13 Last updated: 2019-01-04
Bergqvist, J., Tress, W., Forchheimer, D., Melianas, A., Tang, Z., Haviland, D. & Inganäs, O. (2016). New method for lateral mapping of bimolecular recombination in thin film organic solar cells. Progress in Photovoltaics, 24(8), 1096-1108
Open this publication in new window or tab >>New method for lateral mapping of bimolecular recombination in thin film organic solar cells
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2016 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 24, no 8, p. 1096-1108Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016
Keywords
Organic photovoltaics, imaging, photocurrent, bimolecular recombination, light beam induced current, LBIC, intermodulation
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-123033 (URN)10.1002/pip.2770 (DOI)000380164100007 ()
Note

Funding agencies|Swedish Research Council; Swedish Energy Agency; the Knut and Alice Wallenberg foundation through a Wallenberg Scholar grant to O.I

At the time for thesis presentation publication was in status: Manuscript

Available from: 2015-12-02 Created: 2015-12-02 Last updated: 2017-12-01Bibliographically approved
Tang, Z., Liu, B., Melianas, A., Bergqvist, J., Tress, W., Bao, Q., . . . Zhang, F. (2015). A New Fullerene-Free Bulk-Heterojunction System for Efficient High-Voltage and High-Fill Factor Solution-Processed Organic Photovoltaics. Advanced Materials, 27(11), 1900-+
Open this publication in new window or tab >>A New Fullerene-Free Bulk-Heterojunction System for Efficient High-Voltage and High-Fill Factor Solution-Processed Organic Photovoltaics
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2015 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 27, no 11, p. 1900-+Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Wiley-VCH Verlag, 2015
National Category
Biological Sciences Physical Sciences
Identifiers
urn:nbn:se:liu:diva-116947 (URN)10.1002/adma.201405485 (DOI)000351216500012 ()25645709 (PubMedID)
Note

Funding Agencies|Swedish Energy Agency; Knut and Alice Wallenberg foundation; Swedish research council (VR); Chinese scholarship council

Available from: 2015-04-10 Created: 2015-04-10 Last updated: 2017-12-04
Bai, S., Jin, Y., Liang, X., Ye, Z., Wu, Z., Sun, B., . . . Zhang, F. (2015). Ethanedithiol Treatment of Solution-Processed ZnO Thin Films: Controlling the Intragap States of Electron Transporting Interlayers for Efficient and Stable Inverted Organic Photovoltaics. ADVANCED ENERGY MATERIALS, 5(5), 1401606
Open this publication in new window or tab >>Ethanedithiol Treatment of Solution-Processed ZnO Thin Films: Controlling the Intragap States of Electron Transporting Interlayers for Efficient and Stable Inverted Organic Photovoltaics
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2015 (English)In: ADVANCED ENERGY MATERIALS, ISSN 1614-6832, Vol. 5, no 5, p. 1401606-Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Wiley-VCH Verlag, 2015
Keywords
electron transporting interlayers; intragap states; molecular passivation; organic solar cells; ZnO thin films
National Category
Biological Sciences
Identifiers
urn:nbn:se:liu:diva-116817 (URN)10.1002/aenm.201401606 (DOI)000350754800013 ()
Note

Funding Agencies|National High Technology Research and Development Program of China [2011AA050520]; National Basic Research Program of China (973 Program) [2012CB932402]; National Natural Science Foundation of China [51172203]; Natural Science Funds for Distinguished Young Scholar of Zhejiang Province [R4110189]; Public Welfare Project of Zhejiang Province [2013C31057]; Swedish Energy Agency (Energimyndigheten); Swedish Research Council (VR); European Commission under a Marie Curie Intra-European Fellowship for Career Development

Available from: 2015-04-07 Created: 2015-04-07 Last updated: 2015-06-03
Tang, Z., Elfwing, A., Melianas, A., Bergqvist, J., Bao, Q. & Inganäs, O. (2015). Fully-solution-processed organic solar cells with a highly efficient paper-based light trapping element. Journal of Materials Chemistry A, 3(48), 24289-24296
Open this publication in new window or tab >>Fully-solution-processed organic solar cells with a highly efficient paper-based light trapping element
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2015 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 48, p. 24289-24296Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2015
National Category
Biological Sciences Physical Sciences
Identifiers
urn:nbn:se:liu:diva-123845 (URN)10.1039/c5ta07154b (DOI)000366163000014 ()
Note

Funding Agencies|Swedish Energy Agency; Knut and Alice Wallenberg Foundation through a Wallenberg Scholar grant; Knut and Alice Wallenberg Foundation through the project Power Papers

Available from: 2016-01-11 Created: 2016-01-11 Last updated: 2017-12-01
Infahsaeng, Y., Danna, D., Tang, Z., Pascher, T., Inganäs, O., Sundstrom, V. & Yartsev, A. (2015). Transient photocurrent of bulk heterojunction solar cell characterized by ns-laser and sub-ms LED. In: INTERNATIONAL CONFERENCE ON PHOTONICS SOLUTIONS 2015: . Paper presented at International Conference on Photonics Solutions (ICPS). SPIE-INT SOC OPTICAL ENGINEERING, 9659(UNSP 96591C)
Open this publication in new window or tab >>Transient photocurrent of bulk heterojunction solar cell characterized by ns-laser and sub-ms LED
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2015 (English)In: INTERNATIONAL CONFERENCE ON PHOTONICS SOLUTIONS 2015, SPIE-INT SOC OPTICAL ENGINEERING , 2015, Vol. 9659, no UNSP 96591CConference paper, Published 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.

Place, publisher, year, edition, pages
SPIE-INT SOC OPTICAL ENGINEERING, 2015
Series
Proceedings of SPIE, ISSN 0277-786X ; 9659
Keywords
Transient photocurrent; Organic Solar Cells; Bulk heterojunction; APFO3
National Category
Biological Sciences
Identifiers
urn:nbn:se:liu:diva-124148 (URN)10.1117/12.2195857 (DOI)000366498800046 ()978-1-62841-875-0 (ISBN)
Conference
International Conference on Photonics Solutions (ICPS)
Available from: 2016-01-22 Created: 2016-01-19 Last updated: 2016-01-22
Ma, Z., Dang, D., Tang, Z., Gedefaw, D., Bergqvist, J., Zhu, W., . . . Wang, E. (2014). A Facile Method to Enhance Photovoltaic Performance of Benzodithiophene-Isoindigo Polymers by Inserting Bithiophene Spacer. ADVANCED ENERGY MATERIALS, 4(6)
Open this publication in new window or tab >>A Facile Method to Enhance Photovoltaic Performance of Benzodithiophene-Isoindigo Polymers by Inserting Bithiophene Spacer
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2014 (English)In: ADVANCED ENERGY MATERIALS, ISSN 1614-6832, Vol. 4, no 6Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Wiley-VCH Verlag, 2014
Keywords
conjugated polymers; energy conversion; fullerenes; photochemistry; solar cells
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-106976 (URN)10.1002/aenm.201301455 (DOI)000334790000008 ()
Available from: 2014-06-04 Created: 2014-06-02 Last updated: 2014-06-04
Pranculis, V., Infahsaeng, Y., Tang, Z., Devizis, A., Vithanage, D. A., Ponseca, C. S. J., . . . Sundstrom, V. (2014). Charge Carrier Generation and Transport in Different Stoichiometry APFO3:PC61BM Solar Cells. Journal of the American Chemical Society, 136(32), 11331-11338
Open this publication in new window or tab >>Charge Carrier Generation and Transport in Different Stoichiometry APFO3:PC61BM Solar Cells
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2014 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 136, no 32, p. 11331-11338Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Chemical Society, 2014
National Category
Industrial Biotechnology
Identifiers
urn:nbn:se:liu:diva-110480 (URN)10.1021/ja503301m (DOI)000340442700029 ()25025885 (PubMedID)
Note

Funding Agencies|Swedish and European Research Councils [226136-VISCHEM]; Swedish Energy Agency; Knut and Alice Wallenberg Foundation

Available from: 2014-09-15 Created: 2014-09-12 Last updated: 2017-12-05
Tang, Z. (2014). Chargeand Light Management in Organic Solar Cells. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Chargeand Light Management in Organic Solar Cells
2014 (English)Doctoral 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.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. p. 79
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1567
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-103930 (URN)978-91-7519-419-6 (ISBN)
Public defence
2014-03-07, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-02-03 Created: 2014-02-03 Last updated: 2014-02-03Bibliographically approved
Tang, Z., Tress, W., Bao, Q., Jafari, M. J., Bergqvist, J., Ederth, T., . . . Inganäs, O. (2014). Improving Cathodes with a Polymer Interlayer in Reversed Organic Solar Cells. Advanced Energy Materials, 4(15), Article ID 1400643.
Open this publication in new window or tab >>Improving Cathodes with a Polymer Interlayer in Reversed Organic Solar Cells
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2014 (English)In: Advanced Energy Materials, ISSN 1614-6832, Vol. 4, no 15, article id 1400643Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2014
Keywords
organic solar cells; polymer solar cells; interlayer modification; interfaces; selectivity
National Category
Physical Sciences Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-112636 (URN)10.1002/aenm.201400643 (DOI)000344368500014 ()
Note

Funding Agencies|KAW; Science Council (VR); Swedish Energy Agency; Knut and Alice Wallenberg Foundation KAW through the project Power Papers; Wallenberg Scholar grant

Available from: 2014-12-08 Created: 2014-12-05 Last updated: 2017-01-11Bibliographically approved
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