Ladder-type heteroacene-based dopant-free hole-transporting materials for efficient and stable CsPbI2Br perovskite solar cells

Abstract Dopant-free hole-transporting materials (HTMs) play a vital role in improving the power conversion efficiencies (PCEs) and stability for all-inorganic perovskite solar cells (PVSCs). In this work, two donor-acceptor-donor (D-A-D) type HTMs (L2 and L2-T) were designed and synthesized by using a ladder-type heteroacene core. Compared to L2-T with thiophene spacers, L2 presents suitable energy levels, smooth surface morphology, and improved hole mobility. Consequently, CsPbI2Br PVSC based on L2 delivers a decent PCE of 12.41%, which outperforms the counterpart based on L2-T (11.07%). Whereas, the control device based on dopant-free 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) reveals a relatively low PCE of 9.95%. In addition, both the L2- and L2-T-based devices can maintain over 85% of their original PCEs after 1000 h storage demonstrating their excellent shelf stability. This work highlights the good potential of the ladder-type heteroacene building block for developing dopant-free HTMs toward high-performance CsPbI2Br PVSCs.