Organic–inorganic halide perovskite solar cells (PSCs) have attracted considerable scientific and industrial interest because of their high efficiency and solution processability. As a key component, hole transport materials (HTMs) are critically important for achieving efficient hole extraction and thus high performance. However, the commonly employed organic HTMs such as 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spiro‐bifuorene and poly(triarylamine) (PTAA) are quite expensive due to their complicated synthesis procedures and high purity requirements. Moreover, the instability of these organic compounds further hinders the large‐scale commercialization of PSCs. To address these issues, various inorganic p‐type semiconductors featuring excellent chemical stability, high hole mobility, and suitable energy levels are investigated as promising alternatives to their organic counterparts. Herein, recent advances of inorganic hole conductors for PSCs with a focus on low‐cost fabrication and enhanced long‐term stability are reviewed. A series of unexplored inorganic p‐type semiconductors with desirable optoelectronic properties are also highlighted as promising candidates. In addition, the current challenges and potential strategies are presented to reveal the future opportunities in this research field.

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The last decades have seen an exceptionally rapid rise of a novel type of solar cell based on organic-inorganic hybrid perovskite materials. The efficient solid state perovskite solar cells (PSCs) were initially reported in the middle of 2012. Despite of the fact that the perovskite solar cell was a recent technology at that time, perovskite solar cells have experienced unprecedentedly rapid progress by achieving energy conversion efficiency of 16.2% at the end of 2013. The energy conversion efficiency was enhanced by achieving a confirmed value of 17.9% in early 2014. Power conversion efficiency have risen to over 22% from 3% in only a few years.Furthermore, a broad range of various fabrication methods, novel device architectures, and different p and n types semiconductors have been discovered by scientists up to now. This broad diversity explicitly points the fact that power conversion efficiency is still far off from the possible maximum level of power conversion efficiency. In addition to the aim of the maximum achievable power conversion efficiency, the stability issue of PSCs must be well investigated and addressed in order to commercialize highly efficient PSCs. The choice of hole transport materials (HTMs) has been significant impact on the photovoltaic parameters and long term stability of PSCs. This report aims to elucidate the employment of novel inorganic p-type HTMs in PSC devices.3