Ion-modulated radical doping of spiro-OMeTAD for more efficient and stable perovskite solar cells
Tiankai Zhang, Feng Wang, Hak‐Beom Kim, In Woo Choi, Chuanfei Wang, Eunkyung Cho, Rafał Konefał, Yuttapoom Puttisong, Kosuke Terado, Libor Kobera, Mengyun Chen, Mei Yang, Sai Bai, Bowen Yang, Jiajia Suo, Shih‐Chi Yang, Xianjie Liu, Fan Fu, Hiroyuki Yoshida, Weimin Chen, Jiřı́ Brus, Veaceslav Coropceanu, Anders Hagfeldt, Jean‐Luc Brédas, Mats Fahlman, Dong Suk Kim, Zhangjun Hu, Feng Gao
Abstract
Record power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have been obtained with the organic hole transporter 2,2′,7,7′-tetrakis( N , N -di- p -methoxyphenyl-amine)9,9′-spirobifluorene (spiro-OMeTAD). Conventional doping of spiro-OMeTAD with hygroscopic lithium salts and volatile 4- tert -butylpyridine is a time-consuming process and also leads to poor device stability. We developed a new doping strategy for spiro-OMeTAD that avoids post-oxidation by using stable organic radicals as the dopant and ionic salts as the doping modulator (referred to as ion-modulated radical doping). We achieved PCEs of >25% and much-improved device stability under harsh conditions. The radicals provide hole polarons that instantly increase the conductivity and work function (WF), and ionic salts further modulate the WF by affecting the energetics of the hole polarons. This organic semiconductor doping strategy, which decouples conductivity and WF tunability, could inspire further optimization in other optoelectronic devices.