Hydrophilic Surface-Driven Crystalline Grain Growth of Perovskites on Metal Oxides

Metal oxide charge-transport layers (CTLs) are known to influence the properties and performance of organometal halide perovskite solar cells (PSCs). Accordingly, this work demonstrates, in detail, the crystalline grain growth mechanism of CH3NH3PbI3 (MAPbI(3)) depending on the hydrophilicity of CTLs such as compact (c)-TiO2, mesoporous (mp)-TiO2, SnO2, and NiOx. Importantly, smaller water contact angles of CTLs (11.5 degrees for SnO2; 21.4 degrees for mp-TiO2; 27.8 degrees for NiOx; and 30.7 degrees for c-TiO2) were linked to larger average grain sizes of a top-layered perovskite film (308.2 nm for SnO2; 266.4 nm for mp-TiO2; 209.7 nm for NiOx; and 185.4 nm for c-TiO2), indicating 'hydrophilic surface-driven crystalline grain growth' of MAPbI(3) on metal oxides. Furthermore, by estimating the solubility parameter (delta) of CTLs, we explain that, when Delta delta = delta(CTL) - delta(solvent) is large, the MAPbI(3) grain size increases because of a limited chance of nucleation during the antisolvent-assisted one-step coating process. However, it is notable that the hydrophilic surface of CTLs may induce instability of MAPbI3 under humidity. Finally, the highest power conversion efficiency (similar to 19.03%) was obtained when SnO2 served as an electron-transport layer for the planar heterojunction PSCs.

Automated summary

This study investigates the influence of metal oxide charge-transport layers (CTLs) on the properties of organometal halide perovskite solar cells (PSCs), revealing that the hydrophilicity of CTLs can drive the growth of MAPbI3 crystalline grains and impact the overall power conversion efficiency. Hydrophilic surfaces of CTLs lead to larger perovskite grain sizes, while the highest efficiency is achieved when SnO2 is used as the electron-transport layer in planar heterojunction PSCs.