Benzimidazole Based Hole-Transporting Materials for High-performance Inverted Perovskite Solar Cells

Interfaces play a decisive role in perovskite solar cells' power conversion efficiency and their long-term durability. Small-molecule hole-transporting materials (HTMs) have grabbed enormous attention due to their structural flexibility, material properties, and stabilities, allowing for improved operational durability in perovskite photovoltaics. This study synthesizes and investigates a new class of benzimidazole-based small molecules, named YJS001 and YJS003, serving as the HTMs to enable high-efficiency mixed-cation mixed-halide perovskite solar cells. The benzimidazole-based materials are dopant-free HTMs composed of donor and acceptor building blocks that are designed to engineer the energy level alignment near the HTM/perovskite interface. Mixed-cation mixed-halide perovskites can be grown uniformly on both HTMs with large crystalline grains. It is discovered that the donor-rich YJS003-based solar cell exhibits a high open-circuit voltage of 1.09 V with a champion power conversion efficiency of over 20%. Power-dependent current-voltage characteristics of the solar cells are analyzed, from which the high performance of YJS003's excellent hole mobility and well-aligned energy level is attributed. This work introduces a new class of benzimidazole-based small molecules as HTMs, that paves the path for dopant free interface material development for commercialization of perovskite solar cells.