Progress in CZTS as hole transport layer in perovskite solar cell

Power conversion efficiency of perovskite solar cells (PSC) has improved around 500% in less than five years, with the current highest recorded efficiency of a standalone PSC of 25.2%. One of the significant components of PSCs that contribute to this improvement is the transport layer, necessary in the separation and injection of charge carriers. Over the years, organic hole transport layers (HTLs) such as 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD) have been investigated, developed, and utilized successfully, but facile and low-cost synthesis, good stability, yet efficient HTL remain to be major challenges. Therefore, alternative HTLs based on inorganic materials are being studied. This short review presents progress in the studies of an alternative HTL material for PSCs, Cu2ZnSnS4 (CZTS), known for the ease of synthesis and band tuning, composition based on abundant and non-toxic elements, good electrical properties, and superior stability. Focus is on the effects of integration of CZTS as HTL in PSC, and opportunities for further improvement.