Dopant‐Free Two‐Dimensional Hole Transport Small Molecules Enable Efficient Perovskite Solar Cells

• Published in: Advanced energy materials 2023-03, Vol.13 (11), p.n/a
• Main Authors: Ji, Xiaofei, Zhou, Tong, Fu, Qiang, Wang, Wenxuan, Wu, Ziang, Zhang, Mingtao, Guo, Xugang, Liu, Dongxue, Woo, Han Young, Liu, Yongsheng
• Format: Article
• Language: English
• Subjects: Commercialization; Conjugates; defect passivation; Dopants; dopant‐free; Efficiency; Energy conversion efficiency; Hole mobility; hole transport materials; Lewis base; Orientation; perovskite solar cells; Perovskites; Photovoltaic cells; Solar cells; two‐dimensional conjugated molecules
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.202203756

Developing dopant‐free hole transport materials (HTMs) to replace Spiro‐OMeTAD is a challenging but urgent issue for commercialization of state‐of‐the‐art n‐i‐p structured perovskite solar cells (PSCs). Here, this work proposes an effective two‐dimensional conjugate engineering strategy to tune molecular stacking orientation and improve the hole mobility of dopant‐free small molecule HTMs. For the first time, triphenylamine (TPA) groups are incorporated as side chains of benzo [1,2‐b:4,5‐b′]dithiophene (BDT) unit to extend the longitudinal conjugate, achieving two donor‐acceptor‐acceptor type 2D small molecules, namely XF2 and XF3, which show a dominant face‐on orientation and better hole transport mobility than the linear small molecule XF1. The incorporation of alkoxy Lewis base groups makes XF3 a more effective defect passivator for perovskite surfaces. As a result, the PSCs using pristine XF3 HTM show a dramatically improved efficiency of 20.59% along with improved long‐term stability compared to that of XF1 HTM (power conversion efficiency (PCE) = 18.84%). A champion efficiency of 21.44% is achieved through device engineering for dopant‐free XF3‐based PSCs. The results show that the building block with longitudinal conjugate extension in small molecules plays an essential role in the face‐on orientation morphology and elucidates a key design rule for the dopant‐free small molecule HTMs for high‐performance PSCs. Two A‐D‐A type 2D small molecules with longitudinal conjugate extension using triphenylamine groups as side chains are successfully developed. The 2D small molecules show a dominant face‐on orientation and better hole transport mobility. A champion efficiency of 21.44% is achieved using the dopant‐free 2D small molecule hole transport material in perovskite solar cells along with improved stability.