Efficient Nonfullerene Organic Solar Cells with Small Driving Forces for Both Hole and Electron Transfer.

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Chen, Shangshang 
Wang, Yuming 
Zhang, Lin 
Zhao, Jingbo 
Chen, Yuzhong 

State-of-the-art organic solar cells (OSCs) typically suffer from large voltage loss (Vloss ) compared to their inorganic and perovskite counterparts. There are some successful attempts to reduce the Vloss by decreasing the energy offsets between the donor and acceptor materials, and the OSC community has demonstrated efficient systems with either small highest occupied molecular orbital (HOMO) offset or negligible lowest unoccupied molecular orbital (LUMO) offset between donors and acceptors. However, efficient OSCs based on a donor/acceptor system with both small HOMO and LUMO offsets have not been demonstrated simultaneously. In this work, an efficient nonfullerene OSC is reported based on a donor polymer named PffBT2T-TT and a small-molecular acceptor (O-IDTBR), which have identical bandgaps and close energy levels. The Fourier-transform photocurrent spectroscopy external quantum efficiency (FTPS-EQE) spectrum of the blend overlaps with those of neat PffBT2T-TT and O-IDTBR, indicating the small driving forces for both hole and electron transfer. Meanwhile, the OSCs exhibit a high electroluminescence quantum efficiency (EQEEL ) of ≈1 × 10-4 , which leads to a significantly minimized nonradiative Vloss of 0.24 V. Despite the small driving forces and a low Vloss , a maximum EQE of 67% and a high power conversion efficiency of 10.4% can still be achieved.

charge transfer, organic solar cells, small-molecular acceptors, voltage loss
Journal Title
Advanced Materials
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Engineering and Physical Sciences Research Council (EP/M005143/1)
The work described in this paper was partially supported by the National Basic Research Program of China (973 Program project numbers 2013CB834701 and 2014CB643501), the Shenzhen Technology and Innovation Commission (project numbers JCYJ20170413173814007 and JCYJ20170818113905024), the Hong Kong Research Grants Council (project numbers T23‐407/13 N, N_HKUST623/13, 16305915, 16322416, 606012, 16306117, and 16303917), HK JEBN Limited, HKUST president's office (Project FP201), and the National Science Foundation of China (Grant No. #21374090), the Swedish Energy Agency Energimyndigheten (2016‐010174), the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant No. SFO‐Mat‐LiU #2009‐00971). The authors especially thank Hong Kong Innovation and Technology Commission for the support through projects ITC‐CNERC14SC01 and ITS/083/15.