Suppressed recombination loss in organic photovoltaics adopting a planar-mixed heterojunction architecture

Authors：Jiang, Kui; Zhang, Jie; Zhong, Cheng; Lin, Francis R.^*; Qi, Feng; Li, Qian; Peng, Zhengxing; Kaminsky, Werner; Jang, Sei-Hum; Yu, Jianwei; Deng, Xiang; Hu, Huawei; Shen, Dong; Gao, Feng; Ade, Harald; Xiao, Min; Zhang, Chunfeng^*; Jen, Alex K-Y^*

Source：Nature Energy, 2022, 7(11): 1076-1086.

DOI：10.1038/s41560-022-01138-y

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• CELLS

At present, high-performance organic photovoltaics mostly adopt a bulk-heterojunction architecture, in which exciton dissociation is facilitated by charge-transfer states formed at numerous donor-acceptor (D-A) heterojunctions. However, the spin character of charge-transfer states originated from recombination of photocarriers allows relaxation to the lowest-energy triplet exciton (T-1) at these heterojunctions, causing photocurrent loss. Here we find that this loss pathway can be alleviated in sequentially processed planar-mixed heterojunction (PMHJ) devices, employing donor and acceptor with intrinsically weaker exciton binding strengths. The reduced D-A intermixing in PMHJ alleviates non-geminate recombination at D-A contacts, limiting the chance of relaxation, thus suppressing T-1 formation without sacrificing exciton dissociation efficiency. This resulted in devices with high power conversion efficiencies of >19%. We elucidate the working mechanisms for PMHJs and discuss the implications for material design, device engineering and photophysics, thus providing a comprehensive grounding for future organic photovoltaics to reach their full promise. @@@ Organic solar cells with a bulk-heterojunction architecture suffer from photocurrent loss driven by triplet states. Now, Jiang et al. show that sequentially deposited donor-acceptor planar-mixed heterojunctions suppress triplet formation, enabling efficiencies over 19%.

• Institution
  南京大学; 武汉大学; 中国科学院