Boosting Tin-Perovskite Solar Cell Efficiency Using Direct Arylation Polymerized n-Type Organic Semiconductors As Superior Electron-Transporting Layers

The electron-transporting layer (ETL) plays a crucial role in tin-based perovskite solar cells (TPSCs). However, the high synthesis cost, low mobility, and poor photothermal stability of the widely adopted ETL indene-C60 bisadduct (ICBA) limit TPSC development. Herein, we design and synthesize two n-type semiconducting polymers─PNDI-BT and PNDI-FBT─using direct arylation polymerization as alternative ETLs. Notably, the synthesis cost of PNDI-FBT is only 6% that of ICBA, making it a highly economical option. Both PNDI-BT and PNDI-FBT exhibit better performance compared to ICBA, offering cascade energy-level alignment, enhanced electron mobility, and improved photothermal stability. The fluorinated polymer PNDI-FBT shows even higher electron mobility and stronger interfacial interactions. Thus, the inverted TPSCs incorporating PNDI-FBT as the ETL achieve a remarkable power conversion efficiency of 15.57%, which significantly surpasses that of devices using ICBA (13.34%) and the nonfluorinated counterpart PNDI-BT (14.22%). These findings underscore the potential of n-type polymers as cost-effective ETLs for efficient TPSCs.