Inverted Planar Perovskite Solar Cells Based on NiO_x Nano Film with Enhanced Efficiency and Stability

The organometal halide perovskite (OHP) materials have attracted much attention throughout the world due to their superb optoelectronic properties. Tremendous progress has been made in the OHP based solar cells with increased efficiency from 3.8% to 24.2% within the last decade, benefiting from efforts in the photovoltaic field. However, all the OHP solar cells with highest efficient are based on a normal mesoporous structure with TiO2 at the bottom, which needs high temperature process. The inverted planar structure OHP solar cells based on PEDOT:PSS suffer from low efficiency (lower than 15%) and inferior stability due to degradation of PEDOT:PSS in ambient air. Herein, we employed sol-gel method to fabricate a NiO_x nano film as the hole transporting layer for inverted OHP solar cells. The device performance based on PEDOT:PSS and NiO_x were systematically investigated. It was found that the perovskite films on NiO_x film had larger grain size and thus lower defects) density. The Capacitance-Voltage measurement indicated that the device based on NiO_x exhibited larger built-in potential, which significantly enhanced the open-circuit potential of the OHP solar cells. Furthermore, the solar cell based on NiO_x nano film exhibited excellent stability compared with the PEDOT:PSS based device, due to robust property of NiO_x in ambient air.