Fast and low temperature processed CsPbI3 perovskite solar cells with ZnO as electron transport layer

Black-phased cesium lead triiodide (γ-CsPbI3) inorganic perovskite is one of the most desirable candidates for highly efficient perovskite solar cells (PSCs) due to its intrinsic thermal stability and solvable preparation. The electron transport layer (ETL) plays crucial roles of electron extraction/transport and hole blocking in the devices. Zinc oxide (ZnO) with superior electron mobility and suitable energy level is a promising electron transport material for inorganic PSCs, but adopting ZnO as an ETL in inorganic PSCs is barely reported at present. In this work, we present low-temperature processed ZnO as an ETL in γ-CsPbI3 PSCs. The interesting phenomenon that the transition temperature of γ-CsPbI3 formation on ZnO ETL decreased from 180 °C to 130 °C is observed. The well-matched lattices of ZnO and CsPbI3 as well as nonexistent deprotonation which occurs in MAPbI3 based PSCs indicate ZnO can be a suitable electron transport material for inorganic PSCs. A power conversion efficiency of 12.22% and a high open circuit voltage of 1.14 V are obtained because of the good energy level alignment and the surface contact. This work shows ZnO can be used as a promising ETL in inorganic PSCs.