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  • 1.
    Zhou, Zichun
    et al.
    Chinese Acad Sci, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Liu, Wenrui
    Chinese Acad Sci, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Zhou, Guanqing
    Shanghai Jiao Tong Univ, Peoples R China.
    Zhang, Ming
    Shanghai Jiao Tong Univ, Peoples R China.
    Qian, Deping
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Zhang, Jianyun
    Chinese Acad Sci, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Chen, Shanshan
    Chongqing Univ, Peoples R China; Ulsan Natl Inst Sci and Technol, South Korea.
    Xu, Shengjie
    Chinese Acad Sci, Peoples R China.
    Yang, Changduk
    Ulsan Natl Inst Sci and Technol, South Korea.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Zhu, Haiming
    Zhejiang Univ, Peoples R China.
    Liu, Feng
    Shanghai Jiao Tong Univ, Peoples R China.
    Zhu, Xiaozhang
    Chinese Acad Sci, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Subtle Molecular Tailoring Induces Significant Morphology Optimization Enabling over 16% Efficiency Organic Solar Cells with Efficient Charge Generation2020In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, article id 1906324Article in journal (Refereed)
    Abstract [en]

    Manipulating charge generation in a broad spectral region has proved to be crucial for nonfullerene-electron-acceptor-based organic solar cells (OSCs). 16.64% high efficiency binary OSCs are achieved through the use of a novel electron acceptor AQx-2 with quinoxaline-containing fused core and PBDB-TF as donor. The significant increase in photovoltaic performance of AQx-2 based devices is obtained merely by a subtle tailoring in molecular structure of its analogue AQx-1. Combining the detailed morphology and transient absorption spectroscopy analyses, a good structure-morphology-property relationship is established. The stronger pi-pi interaction results in efficient electron hopping and balanced electron and hole mobilities attributed to good charge transport. Moreover, the reduced phase separation morphology of AQx-2-based bulk heterojunction blend boosts hole transfer and suppresses geminate recombination. Such success in molecule design and precise morphology optimization may lead to next-generation high-performance OSCs.

  • 2.
    Yao, Huifeng
    et al.
    Chinese Acad Sci, Peoples R China.
    Cui, Yong
    Univ Chinese Acad Sci, Peoples R China.
    Qian, Deping
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ponseca, Carlito
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Honarfar, Alireza
    Lund Univ, Sweden.
    Xu, Ye
    Univ Chinese Acad Sci, Peoples R China.
    Xin, Jingming
    Xi An Jiao Tong Univ, Peoples R China.
    Chen, Zhenyu
    Xi An Jiao Tong Univ, Peoples R China.
    Hong, Ling
    Univ Chinese Acad Sci, Peoples R China.
    Gao, Bowei
    Univ Chinese Acad Sci, Peoples R China.
    Yu, Runnan
    Univ Chinese Acad Sci, Peoples R China.
    Zu, Yunfei
    Univ Chinese Acad Sci, Peoples R China.
    Ma, Wei
    Xi An Jiao Tong Univ, Peoples R China.
    Chabera, Pavel
    Lund Univ, Sweden.
    Pullerits, Tonu
    Lund Univ, Sweden.
    Yartsev, Arkady
    Lund Univ, Sweden.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Hou, Jianhui
    Univ Chinese Acad Sci, Peoples R China.
    14.7% Efficiency Organic Photovoltaic Cells Enabled by Active Materials with a Large Electrostatic Potential Difference2019In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 141, no 19, p. 7743-7750Article in journal (Refereed)
    Abstract [en]

    Although significant improvements have been achieved for organic photovoltaic cells (OPVs), the top-performing devices still show power conversion efficiencies far behind those of commercialized solar cells. One of the main reasons is the large driving force required for separating electron-hole pairs. Here, we demonstrate an efficiency of 14.7% in the single-junction OPV by using a new polymer donor PTO2 and a nonfullerene acceptor IT-4F. The device possesses an efficient charge generation at a low driving force. Ultrafast transient absorption measurements probe the formation of loosely bound charge pairs with extended lifetime that impedes the recombination of charge carriers in the blend. The theoretical studies reveal that the molecular electrostatic potential (ESP) between PTO2 and IT-4F is large, and the induced intermolecular electric field may assist the charge generation. The results suggest OPVs have the potential for further improvement by judicious modulation of ESP.

  • 3.
    Hopper, Thomas R.
    et al.
    Imperial Coll London, England.
    Qian, Deping
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Yang, Liyan
    Chinese Acad Sci, Peoples R China.
    Wang, Xiaohui
    Xi An Jiao Tong Univ, Peoples R China.
    Zhou, Ke
    Xi An Jiao Tong Univ, Peoples R China.
    Kumar, Rhea
    Imperial Coll London, England.
    Ma, Wei
    Xi An Jiao Tong Univ, Peoples R China.
    He, Chang
    Chinese Acad Sci, Peoples R China.
    Hou, Jianhui
    Chinese Acad Sci, Peoples R China.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Bakulin, Artem A.
    Imperial Coll London, England.
    Control of Donor-Acceptor Photophysics through Structural Modification of a "Twisting" Push-Pull Molecule2019In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 31, no 17, p. 6860-6869Article in journal (Refereed)
    Abstract [en]

    In contemporary organic solar cell (OSC) research, small A-D-A molecules comprising electron donor (D) and acceptor (A) units are increasingly used as a means to control the optoelectronic properties of photovoltaic blends. Slight structural variations to these A-D-A molecules can result in profound changes to the performance of the OSCs. Herein, we study two A-D-A molecules, BTCN-O and BTCN-M, which are identical in structure apart from a subtle difference in the position of alkyl chains, which force the molecules to adopt different equilibrium conformations. These steric effects cause the respective molecules to work better as an electron donor and acceptor when blended with benchmark acceptor and donor materials (PC71BM and PBDB-T). We study the photophysics of these "D:A" blends and devices using a combination of steady-state and time-resolved spectroscopic techniques. Time-resolved photoluminescence reveals the impact of the molecular conformation on the quenching of the A-D-A emission when BTCN-O and BTCN-M are blended with PBDB-T or PC71BM. Ultrafast broadband transient absorption spectroscopy demonstrates that the dynamics of charge separation are essentially identical when comparing BTCN-M and BTCN-O based blends, but the recombination dynamics are quite dissimilar. This suggests that the device performance is ultimately determined by the morphology of the blends imposed by the A-D-A conformation. This notion is supported by X-ray scattering measurements on the "D:A" films, electroluminescence data, and pump-push-photocurrent spectroscopy on the "D:A" devices. Our findings provide insight into the remarkable structure-function relationship in A-D-A molecules and emphasize the need for careful morphological and energetic considerations when designing high-performance OSCs.

  • 4.
    Yu, Liyang
    et al.
    Sichuan Univ, Peoples R China; Chalmers Univ Technol, Sweden.
    Qian, Deping
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Marina, Sara
    Univ Basque Country, Spain; Univ Basque Country, Spain.
    Nugroho, Ferry A. A.
    Chalmers Univ Technol, Sweden.
    Sharma, Anirudh
    Flinders Univ S Australia, Australia; Univ Bordeaux, France.
    Hultmark, Sandra
    Chalmers Univ Technol, Sweden.
    Hofmann, Anna I.
    Chalmers Univ Technol, Sweden.
    Kroon, Renee
    Chalmers Univ Technol, Sweden.
    Benduhn, Johannes
    Tech Univ Dresden, Germany; Tech Univ Dresden, Germany.
    Smilgies, Detlef-M.
    CHESS, NY 14850 USA.
    Vandewal, Koen
    Hasselt Univ, Belgium.
    Andersson, Mats R.
    Flinders Univ S Australia, Australia.
    Langhammer, Christoph
    Chalmers Univ Technol, Sweden.
    Martin, Jaime
    Univ Basque Country, Spain; Univ Basque Country, Spain; Ikerbasque, Spain.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Mueller, Christian
    Chalmers Univ Technol, Sweden.
    Diffusion-Limited Crystallization: A Rationale for the Thermal Stability of Non-Fullerene Solar Cells2019In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 24, p. 21766-21774Article in journal (Refereed)
    Abstract [en]

    Organic solar cells are thought to suffer from poor thermal stability of the active layer nanostructure, a common belief that is based on the extensive work that has been carried out on fullerene-based systems. We show that a widely studied non-fullerene acceptor, the indacenodithienothiophene-based acceptor ITIC, crystallizes in a profoundly different way as compared to fullerenes. Although fullerenes are frozen below the glass-transition temperature T-g of the photovoltaic blend, ITIC can undergo a glass-crystal transition considerably below its high T-g of similar to 180 degrees C. Nanoscopic crystallites of a low-temperature polymorph are able to form through a diffusion-limited crystallization process. The resulting fine-grained nanostructure does not evolve further with time and hence is characterized by a high degree of thermal stability. Instead, above T-g, the low temperature polymorph melts, and micrometer-sized crystals of a high-temperature polymorph develop, enabled by more rapid diffusion and hence long-range mass transport. This leads to the same detrimental decrease in photovoltaic performance that is known to occur also in the case of fullerene-based blends. Besides explaining the superior thermal stability of non-fullerene blends at relatively high temperatures, our work introduces a new rationale for the design of bulk heterojunctions that is not based on the selection of high-T-g materials per se but diffusion-limited crystallization. The planar structure of ITIC and potentially other non-fullerene acceptors readily facilitates the desired glass-crystal transition, which constitutes a significant advantage over fullerenes, and may pave the way for truly stable organic solar cells.

  • 5.
    Yao, Huifeng
    et al.
    Chinese Acad Sci, Peoples R China.
    Qian, Deping
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Zhang, Hao
    Chinese Acad Sci, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Qin, Yunpeng
    Chinese Acad Sci, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Xu, Bowei
    Chinese Acad Sci, Peoples R China.
    Cui, Yong
    Chinese Acad Sci, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Yu, Runnan
    Chinese Acad Sci, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Hou, Jianhui
    Chinese Acad Sci, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Critical Role of Molecular Electrostatic Potential on Charge Generation in Organic Solar Cells2018In: Chinese journal of chemistry, ISSN 1001-604X, E-ISSN 1614-7065, Vol. 36, no 6, p. 491-494Article in journal (Refereed)
    Abstract [en]

    Revealing the charge generation is a crucial step to understand the organic photovoltaics. Recent development in non-fullerene organic solar cells (OSCs) indicates efficient charge separation even with negligible energetic offset between the donor and acceptor materials. These new findings trigger a critical question concerning the charge separation mechanism in OSCs, traditionally believed to result from sufficient energetic offset between the polymer donor and fullerene acceptor. We propose a new mechanism, which involves the molecular electrostatic potential, to explain efficient charge separation in non-fullerene OSCs. Together with the new mechanism, we demonstrate a record efficiency of similar to 12% for systems with negligible energetic offset between donor and acceptor materials. Our analysis also rationalizes different requirement of the energetic offset between fullerene-based and non-fullerene OSCs, and paves the way for further design of OSC materials with both high photocurrent and high photovoltage at the same time.

  • 6.
    Qian, Deping
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Zheng, Zilong
    Georgia Inst Technol, GA 30332 USA; Georgia Inst Technol, GA 30332 USA.
    Yao, Huifeng
    Chinese Acad Sci, Peoples R China.
    Tress, Wolfgang
    Ecole Polytech Fed Lausanne, Switzerland.
    Hopper, Thomas R.
    Imperial Coll London, England.
    Chen, Shula
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Li, Sunsun
    Chinese Acad Sci, Peoples R China.
    Liu, Jing
    Hong Kong Univ Sci and Technol, Peoples R China; Hong Kong Univ Sci and Technol, Peoples R China.
    Chen, Shangshang
    Hong Kong Univ Sci and Technol, Peoples R China; Hong Kong Univ Sci and Technol, Peoples R China.
    Zhang, Jiangbin
    Imperial Coll London, England; Univ Cambridge, England.
    Liu, Xiaoke
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Gao, Bowei
    Chinese Acad Sci, Peoples R China.
    Ouyang, Liangqi
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Jin, Yingzhi
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    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.
    Coropceanu, Veaceslav
    Georgia Inst Technol, GA 30332 USA; Georgia Inst Technol, GA 30332 USA.
    Bredas, Jean-Luc
    Georgia Inst Technol, GA 30332 USA; Georgia Inst Technol, GA 30332 USA.
    Yan, He
    Hong Kong Univ Sci and Technol, Peoples R China; Hong Kong Univ Sci and Technol, Peoples R China.
    Hou, Jianhui
    Chinese Acad Sci, Peoples R China.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Bakulin, Artem A.
    Imperial Coll London, England.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Design rules for minimizing voltage losses in high-efficiency organic solar cells2018In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 17, no 8, p. 703-+Article in journal (Refereed)
    Abstract [en]

    The open-circuit voltage of organic solar cells is usually lower than the values achieved in inorganic or perovskite photovoltaic devices with comparable bandgaps. Energy losses during charge separation at the donor-acceptor interface and non-radiative recombination are among the main causes of such voltage losses. Here we combine spectroscopic and quantum-chemistry approaches to identify key rules for minimizing voltage losses: (1) a low energy offset between donor and acceptor molecular states and (2) high photoluminescence yield of the low-gap material in the blend. Following these rules, we present a range of existing and new donor-acceptor systems that combine efficient photocurrent generation with electroluminescence yield up to 0.03%, leading to non-radiative voltage losses as small as 0.21 V. This study provides a rationale to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.

  • 7.
    Wang, Yuming
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Nanjing Tech Univ, Peoples R China.
    Jafari, Mohammad Javad
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering.
    Wang, Nana
    Nanjing Tech Univ, Peoples R China.
    Qian, Deping
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ederth, Thomas
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering.
    Moons, Ellen
    Karlstad Univ, Sweden.
    Wang, Jianpu
    Nanjing Tech Univ, Peoples R China.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Huang, Wei
    Nanjing Tech Univ, Peoples R China.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Light-induced degradation of fullerenes in organic solar cells: a case study on TQ1:PC71BM2018In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, no 25, p. 11884-11889Article in journal (Refereed)
    Abstract [en]

    The stability of organic solar cells (OSCs) is critical for practical applications of this emerging technology. Unfortunately, in spite of intensive investigations, the degradation mechanisms in OSCs have not been clearly understood yet. In this report, we employ a range of spectroscopic and transport measurements, coupled with drift-diffusion modelling, to investigate the light-induced degradation mechanisms of fullerene-based OSCs. We find that trap states formed in the fullerene phase under illumination play a critical role in the degradation of the open-circuit voltage (V-OC) in OSCs. Our results indicate that the degradation is intrinsic to the fullerenes in OSCs and that alternative acceptor materials are desired for the development of stable OSCs.

  • 8.
    Wang, Yuming
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Qian, Deping
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Cui, Yong
    Chinese Acad Sci, Peoples R China.
    Zhang, Huotian
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Hou, Jianhui
    Chinese Acad Sci, Peoples R China.
    Vandewal, Koen
    Hasselt Univ, Belgium.
    Kirchartz, Thomas
    Forschungszentrum Julich, Germany; Univ Duisburg Essen, Germany; Univ Duisburg Essen, Germany.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Optical Gaps of Organic Solar Cells as a Reference for Comparing Voltage Losses2018In: ADVANCED ENERGY MATERIALS, ISSN 1614-6832, Vol. 8, no 28, article id 1801352Article in journal (Refereed)
    Abstract [en]

    The voltage loss, determined by the difference between the optical gap (E-g) and the open-circuit voltage (V-OC), is one of the most important parameters determining the performance of organic solar cells (OSCs). However, the variety of different methods used to determine E-g makes it hard to fairly compare voltages losses among different material systems. In this paper, the authors discuss and compare various E-g determination methods and show how they affect the detailed calculation of voltage losses, as well as predictions of the maximum achievable power conversion efficiency. The aim of this paper is to make it possible for the OSC community to compare voltage losses in a consistent and reasonable way. It is found that the voltage losses for strongly absorbed photons in state-of-the-art OSCs are not much less than 0.6 V, which still must be decreased to further enhance efficiency.

  • 9.
    Yang, Fan
    et al.
    Chinese Academic Science, Peoples R China; University of Chinese Academic Science, Peoples R China.
    Qian, Deping
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Hesham Balawi, Ahmed
    KAUST, Saudi Arabia.
    Wu, Yang
    Xi An Jiao Tong University, Peoples R China.
    Ma, Wei
    Xi An Jiao Tong University, Peoples R China.
    Laquai, Frederic
    KAUST, Saudi Arabia.
    Tang, Zheng
    Technical University of Dresden, Germany.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Li, Weiwei
    Chinese Academic Science, Peoples R China.
    Performance limitations in thieno[3,4-c] pyrrole4,6-dione-based polymer: ITIC solar cells2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 35, p. 23990-23998Article in journal (Refereed)
    Abstract [en]

    We report a systematic study of the efficiency limitations of non-fullerene organic solar cells that exhibit a small energy loss (E-loss) between the polymer donor and the non-fullerene acceptor. To clarify the impact of Eloss on the performance of the solar cells, three thieno[3,4-c] pyrrole-4,6-dione-based conjugated polymers (PTPD3T, PTPD2T, and PTPDBDT) are employed as the electron donor, which all have complementary absorption spectra compared with the ITIC acceptor. The corresponding photovoltaic devices show that low Eloss (0.54 eV) in PTPDBDT: ITIC leads to a high open-circuit voltage (Voc) of 1.05 V, but also to a small quantum efficiency, and in turn photocurrent. The high Voc or small energy loss in the PTPDBDT-based solar cells is a consequence of less non-radiative recombination, whereas the low quantum efficiency is attributed to the unfavorable micro-phase separation, as confirmed by the steady-state and time-resolved photoluminescence experiments, grazing-incidence wide-angle X-ray scattering, and resonant soft X-ray scattering (R-SoXS) measurements. We conclude that to achieve high performance non-fullerene solar cells, it is essential to realize a large Voc with small Eloss while simultaneously maintaining a high quantum efficiency by manipulating the molecular interaction in the bulk-heterojunction.

  • 10.
    Qian, Deping
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Studies of Voltage Losses in Organic Solar Cells2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Organic photovoltaic (OPV) devices based on semiconducting polymers and small molecules are potential alternatives to inorganic solar cells, owing to their advantages of being inexpensive, lightweight, flexible and suitable for roll-to-roll production. The state of art organic solar cells (OSCs) performed power conversion efficiencies (PCEs) over 13%.

    The quantum efficiency losses in OSCs have been significantly reduced within the charge generation and extraction processes, resulting in high EQEPV (70-90%) and high FF (70-80%). Whereas, large voltage losses (Δ𝑉 = 𝐸𝑔/𝑞 − 𝑉𝑂𝐶) were observed in conventional fullerene based solar cells, and it has been the main limiting factor for further OPV advancement. Therefore, strategies to reduce the voltage losses are required.

    In this thesis, newly designed non-fullerene (NF) acceptors are used to construct novel material systems for high efficiency solar cells. In particular, we studied the hole transfer in these fullerene free systems. We also reported a NF system that exhibit ultrafast and efficient charge separation despite a negligible driving force, as ECT is nearly identical to 𝐸𝑔. Moreover, the small driving force is found to have minimal detrimental effects on charge transfer dynamics of the OSCs. We demonstrate a NF based OSC with efficiency of 9.5% and internal quantum efficiency nearly 90% despite a low voltage loss of 0.61 V. This creates a path towards highly efficient OSCs with a low voltage loss.

    CT states in OSCs are also investigated, since VOC is governed by the CT energy (ECT), which is found as 𝑞𝑉𝑂𝐶 = 𝐸𝐶𝑇 − 0.6 in a large set of fullerene based solar cells. In order to reduce these recombination losses from CT states, we explored polymer-diPDI systems which exhibited weakened D-A coupling strength, due to the steric hindrance effect. The radiative recombination losses at D/A interface in these NF devices are all reduced to less than 0.18 eV. In particular, in some cases, the additional emission from pure material is favorable for suppressing the non-radiative CT states decay. Consequently, the recombination losses in these NF systems are reduced to 0.5 eV, while the charge generation is still efficient as confirmed by PL quenching and EQEPV.

    Novel material systems based on non-fullerene acceptors are investigated. The systems performed energy offsets (ΔHOMO or ΔLUMO) less than 0.15eV, resulting in the same energy of CT states and bulk excitons. In this regard, the charge transfer energy loss is minimized. We also found that the EL spectra as well as the EQEEL of the blend solar cells are similar with that of lower gap components in blends. Thus the non-radiative voltage losses are reduced to < 0.3V and small voltage loss of 0.5-0.7V are obtained. Meanwhile, the charge generation in systems are still efficient and high EQEPV of 50-70% can be achieved. It confirms that there is no intrinsic limit for the VOC and efficiency of OPVs as compared with other photovoltaic technologies.

    List of papers
    1. Modulating molecular aggregation by facile heteroatom substitution of diketopyrrolopyrrole based small molecules for efficient organic solar cells
    Open this publication in new window or tab >>Modulating molecular aggregation by facile heteroatom substitution of diketopyrrolopyrrole based small molecules for efficient organic solar cells
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    2015 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 48, p. 24349-24357Article in journal (Refereed) Published
    Abstract [en]

    In conjugated polymers and small molecules of organic solar cells, aggregation induced by intermolecular interactions governs the performance of photovoltaics. However, little attention has been paid to the connection between molecular structure and aggregation within solar cells based on soluble small molecules. Here we demonstrate modulation of intermolecular aggregation of two synthesized molecules through heteroatom substitution to develop an understanding of the role of aggregation in conjugated molecules. Molecule 1 (M1) based on 2-ethylhexyloxy-benzene substituted benzo[1,2-b:4,5-b]dithiophene (BDTP) and diketopyrrolopyrrole (DPP) displays strong aggregation in commonly used organic solvents, which is reduced in molecule 2 (M2) by facile oxygen atom substitution on the BDTP unit confirmed by absorption spectroscopy and optical microscopy, while it successfully maintains molecular planarity and favorable charge transport characteristics. Solar cells based on M2 exhibit more than double the photocurrent of devices based on M1 and yield a power conversion efficiency of 5.5%. A systematic investigation of molecular conformation, optoelectronic properties, molecular packing and crystallinity as well as film morphology reveals structure dependent aggregation responsible for the performance difference between the two conjugated molecules.

    Place, publisher, year, edition, pages
    ROYAL SOC CHEMISTRY, 2015
    National Category
    Biological Sciences Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:liu:diva-123846 (URN)10.1039/c5ta06501a (DOI)000366163000022 ()
    Note

    Funding Agencies|Swedish Energy Agency; China Scholarship Council (CSC)

    Available from: 2016-01-11 Created: 2016-01-11 Last updated: 2017-12-01
    2. A fused-ring based electron acceptor for efficient non-fullerene polymer solar cells with small HOMO offset
    Open this publication in new window or tab >>A fused-ring based electron acceptor for efficient non-fullerene polymer solar cells with small HOMO offset
    Show others...
    2016 (English)In: NANO ENERGY, ISSN 2211-2855, Vol. 27, p. 430-438Article in journal (Refereed) Published
    Abstract [en]

    A non-fullerene electron acceptor bearing a novel backbone with fused 10-heterocyclic ring (in-dacenodithiopheno-indacenodiselenophene), denoted by IDTIDSe-IC is developed for fullerene free polymer solar cells. IDTIDSe-IC exhibits a low band gap (E-g=1.52 eV) and strong absorption in the 600850 nm region. Combining with a large band gap polymer J51 (E-g=1.91 eV) as donor, broad absorption coverage from 300 nm to 800 nm is obtained due to complementary absorption of J51 and IDTIDSe-IC, which enables a high PCE of 8.02% with a V-oc of 0.91 V, a J(SC) of 15.16 mA/cm(2) and a FF of 58.0% in the corresponding PSCs. Moreover, the EQE of 50-65% is achieved in the absorption range of IDTIDSe-IC with only about 0.1 eV HOMO difference between J51 and IDTIDSe-IC. (C) 2016 Elsevier Ltd. All rights reserved.

    Place, publisher, year, edition, pages
    ELSEVIER SCIENCE BV, 2016
    Keywords
    Non-fullerene acceptor; Indacenodithiophene; Polymer solar cells
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-132487 (URN)10.1016/j.nanoen.2016.07.019 (DOI)000384910500047 ()
    Note

    Funding Agencies|National Natural Science Foundation of China [21504062, 21572152]; China Postdoctoral Science Foundation [2015M581853]; Jiangsu Province Postdoctoral Science Foundation [1501024B]; Vinnova [2015-04751]; China Scholarship Council (CSC) [201306730002]; Swedish Research Council (VR) [621-2013-5561]; Swedish Energy Agency [EM 42033-1]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Collaborative Innovation Center of Suzhou Nano Science and Technology; Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)

    Available from: 2016-11-13 Created: 2016-11-12 Last updated: 2017-08-18
    3. Fast charge separation in a non-fullerene organic solar cell with a small driving force
    Open this publication in new window or tab >>Fast charge separation in a non-fullerene organic solar cell with a small driving force
    Show others...
    2016 (English)In: NATURE ENERGY, ISSN 2058-7546, Vol. 1, article id 16089Article in journal (Refereed) Published
    Abstract [en]

    Fast and efficient charge separation is essential to achieve high power conversion efficiency in organic solar cells (OSCs). In state-of-the-art OSCs, this is usually achieved by a significant driving force, defined as the offset between the bandgap (E-gap) of the donor/acceptor materials and the energy of the charge transfer (CT) state (E-CT), which is typically greater than 0.3 eV. The large driving force causes a relatively large voltage loss that hinders performance. Here, we report non-fullerene OSCs that exhibit ultrafast and efficient charge separation despite a negligible driving force, as E-CT is nearly identical to E-gap. Moreover, the small driving force is found to have minimal detrimental effects on charge transfer dynamics of the OSCs. We demonstrate a non-fullerene OSC with 9.5% efficiency and nearly 90% internal quantum efficiency despite a low voltage loss of 0.61V. This creates a path towards highly efficient OSCs with a low voltage loss.

    Place, publisher, year, edition, pages
    NATURE PUBLISHING GROUP, 2016
    National Category
    Other Physics Topics
    Identifiers
    urn:nbn:se:liu:diva-135409 (URN)10.1038/NENERGY.2016.89 (DOI)000394175200001 ()
    Note

    Funding Agencies|National Basic Research Program of China (973 Program) [2013CB834701, 2014CB643501]; Hong Kong Research Grants Council [T23-407/13 N, N_HKUST623/13, 606012]; HK JEBN Limited; National Science Foundation of China [21374090, 51361165301]; Office of Naval Research [N000141410531, N000141512322, N000141310526 P00002]; Office of Science, Office of Basic Energy Sciences, of the US Department of Energy [DE-AC02-05CH11231]; Swedish Research Council (VR) [330-2014-6433]; Swedish Research Council (FORMAS) [942-2015-1253]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (faculty grant SFO-Mat-LiU) [2009-00971]; European Commission [691210, INCA 600398]; Wallenberg Scholar grant

    Available from: 2017-03-14 Created: 2017-03-14 Last updated: 2017-11-01
  • 11.
    Li, Yongxi
    et al.
    Soochow University, Peoples R China; Chinese Academic Science, Peoples R China.
    Qian, Deping
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Zhong, Lian
    Chinese Academic Science, Peoples R China; University of Chinese Academic Science, Peoples R China.
    Lin, Jiu-Dong
    Soochow University, Peoples R China.
    Jiang, Zuo-Quan
    Soochow University, Peoples R China.
    Zhang, Zhi-Guo
    Chinese Academic Science, Peoples R China; University of Chinese Academic Science, Peoples R China.
    Zhang, Zhanjun
    Chinese Academic Science, Peoples R China; University of Chinese Academic Science, Peoples R China.
    Li, Yongfang
    Soochow University, Peoples R China; Chinese Academic Science, Peoples R China.
    Liao, Liang-Sheng
    Soochow University, Peoples R China.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    A fused-ring based electron acceptor for efficient non-fullerene polymer solar cells with small HOMO offset2016In: NANO ENERGY, ISSN 2211-2855, Vol. 27, p. 430-438Article in journal (Refereed)
    Abstract [en]

    A non-fullerene electron acceptor bearing a novel backbone with fused 10-heterocyclic ring (in-dacenodithiopheno-indacenodiselenophene), denoted by IDTIDSe-IC is developed for fullerene free polymer solar cells. IDTIDSe-IC exhibits a low band gap (E-g=1.52 eV) and strong absorption in the 600850 nm region. Combining with a large band gap polymer J51 (E-g=1.91 eV) as donor, broad absorption coverage from 300 nm to 800 nm is obtained due to complementary absorption of J51 and IDTIDSe-IC, which enables a high PCE of 8.02% with a V-oc of 0.91 V, a J(SC) of 15.16 mA/cm(2) and a FF of 58.0% in the corresponding PSCs. Moreover, the EQE of 50-65% is achieved in the absorption range of IDTIDSe-IC with only about 0.1 eV HOMO difference between J51 and IDTIDSe-IC. (C) 2016 Elsevier Ltd. All rights reserved.

  • 12.
    Liu, Jing
    et al.
    Hong Kong University of Science and Technology, Peoples R China; Hong Kong University of Science and Technology, Peoples R China.
    Chen, Shangshang
    Hong Kong University of Science and Technology, Peoples R China; Hong Kong University of Science and Technology, Peoples R China.
    Qian, Deping
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Gautam, Bhoj
    North Carolina State University, NC 27695 USA.
    Yang, Guofang
    Hong Kong University of Science and Technology, Peoples R China; Hong Kong University of Science and Technology, Peoples R China; Xi An Jiao Tong University, Peoples R China.
    Zhao, Jingbo
    Hong Kong University of Science and Technology, Peoples R China; Hong Kong University of Science and Technology, Peoples R China.
    Bergqvist, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Zhang, Fengling
    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.
    Ade, Harald
    North Carolina State University, NC 27695 USA.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Gundogdu, Kenan
    North Carolina State University, NC 27695 USA.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Yan, He
    Hong Kong University of Science and Technology, Peoples R China; Hong Kong University of Science and Technology, Peoples R China; Hong Kong University of Science and Technology, Peoples R China.
    Fast charge separation in a non-fullerene organic solar cell with a small driving force2016In: NATURE ENERGY, ISSN 2058-7546, Vol. 1, article id 16089Article in journal (Refereed)
    Abstract [en]

    Fast and efficient charge separation is essential to achieve high power conversion efficiency in organic solar cells (OSCs). In state-of-the-art OSCs, this is usually achieved by a significant driving force, defined as the offset between the bandgap (E-gap) of the donor/acceptor materials and the energy of the charge transfer (CT) state (E-CT), which is typically greater than 0.3 eV. The large driving force causes a relatively large voltage loss that hinders performance. Here, we report non-fullerene OSCs that exhibit ultrafast and efficient charge separation despite a negligible driving force, as E-CT is nearly identical to E-gap. Moreover, the small driving force is found to have minimal detrimental effects on charge transfer dynamics of the OSCs. We demonstrate a non-fullerene OSC with 9.5% efficiency and nearly 90% internal quantum efficiency despite a low voltage loss of 0.61V. This creates a path towards highly efficient OSCs with a low voltage loss.

1 - 12 of 12
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