Recent advancements in the hole transporting layers of perovskite solar cells

One of the emerging technologies in photovoltaic research is organic–inorganic metal halide perovskite solar cells (PSCs). PSCs have a maximum power conversion efficiency (PCE) of >25%, which is comparable to traditional silicon solar cells. Even though perovskite solar cells have demonstrated excellent performance in recent years, commercialization remains a long way off. The presence of unstable hole transporting layers (HTLs) is one of the primary reasons for this. As a result, further development of PSCs toward scalable production remains heavily reliant on the development of innovative low-cost, high-efficiency materials that can be used as HTLs. We discussed the recent advances in various types of organic and inorganic HTLs in this review. The effect of these hole-transporting materials (HTMs) on cell performance and stability in particular has been summarised in order to provide some guidance for the future development of PSCs.