Recent progress in organic hole-transporting materials with 4-anisylamino-based end caps for efficient perovskite solar cells

Perovskite solar cells (PVSCs) have emerged as a promising photovoltaic technology and have attracted wide research interest due to their outstanding photovoltaic performance, low cost, and the ability to fabricate large-area devices. An impressive certified power conversion efficiency (PCE) of 25.2% has been achieved, demonstrating the excellent potential of PVSCs for future applications. Hole-transporting materials play a key role in improving the device performance of PVSCs by facilitating the extraction of photogenerated holes and their transport from the perovskite layer to the anode. This review provides a brief introduction to PVSCs and summarizes the recent progress in small molecule hole-transporting materials (SM-HTMs) bearing various cores and different 4-anisylamino-based end caps. We classify the end caps into N,N-di-4-anisylamino (DAA), 4-(N,N-di-4-anisylamino)benzo (DAB), and N3, N6(or N2, N7)-bis(di-4-anisylamino)-9H-carbazole (3,6-DAC or 2,7-DAC) groups. We also review the core type, end cap position and number, how these affect the overall properties of the SM-HTMs, and the resultant PVSC device performances. Finally, the challenges and perspectives for the future development of SM-HTMs are presented. Graphic abstract