Inorganic Hole Transporting Materials for Stable and High Efficiency Perovskite Solar Cells

Organic inorganic hybrid perovskite solar cells (PSCs) have received considerable attentions due to their low cost, easy fabrication, and high power conversion efficiency (PCE), which A achieved a certified PCE of 22.7%. To date, most of high efficiency PSCs were fabricated based on organic hole transporting materials (HTMs) such as molecular spiro-MeOTAD or polymeric PTAA. However, poor stability of PSCs limits its large scale commercial application because of use of additives like tert-butylpyridine (t-BP) and lithium salt. Moreover, relatively low-temperature degradation of organic HTMs is responsible for poor thermal stability of PSCs. Consequently, HTM play a crucial role in realization of efficient and stable PSCs. In order to improve the stability of PCSs, various inorganic HTMs have been developed and applied into PSCs. Recently, the devices based on CuSCN and Cu:NiOx HTMs have demonstrated PCEs over 20%, which is comparable to PCEs of devices based on organic HTMs. Most importantly, stability of PCSs are much improved by the inorganic HTM, which indicates clearly that inorganic HTMs are promising alternative to organic HTMs. Herein, we review recent progress on application of inorganic HTMs in PSCs. We highlight the importance of systematic engineering for each layer and respective interface in the whole device for further improvement of PCE and stability.