Thin-film formation of 2D MoS2 and its application as a hole-transport layer in planar perovskite solar cells

We have introduced centrifugally-cast thin-film formation technique to 2D transition metal dichalcogenides (TMDs) formed through a liquid based exfoliation method. The film-formation technique has evidenced a growth of uniform and homogeneous thin-films of single or a-few-layered MoS2; the thin-films have been introduced as a charge-transport layer in perovskite solar cells. From scanning tunneling spectroscopy and thereof the density of states of the 2D semiconductor, we have observed that the band-edges of MoS2 formed a type-II band-alignment with the commonly-used organic-inorganic lead halide (CH3NH3PbI3) perovskite when the 2D material was subjected to an ozone-treatment. We thereafter formed p-i-n heterojunction planar perovskite solar cells with the thin-film of 2H-MoS2 so that charge separation can occur at the MoS2 vertical bar perovskite interface. In this work, we also report device characteristics and impedance spectroscopy of the heterojunctions, which were optimized for a small series-resistance and a large shunt-resistance.