In-situ monitored chemical bath deposition of planar NiO layer for inverted perovskite solar cell with enhanced efficiency

As a convenient, low-cost and up-scalable solution route, chemical bath deposition (CBD) has exhibited impressive advantages in fabricating electron transporting materials like SnO2, achieving record efficiencies for regular n-i-p perovskite solar cells (PSCs). However, for the hysteresis-free and potentially more stable inverted p-i-n PSCs, CBD processing is rarely studied to improve the device performance. In this work, we first present a CBD planar NiOx film as the efficient hole transport layer for the inverted perovskite solar cells (IPSCs). The morphologies and semiconducting properties of the NiOx film can be adjusted by varying the concentration of [Ni(H2O)x(NH3)6-x]2+ cation via in-situ monitoring of the CBD reaction process. The characterizations of ultraviolet photoelectron spectroscopy, transient absorption spectroscopy, time-resolved photoluminescence suggest that the CBD planar NiOx film possesses enhanced conductivity and aligned energy band levels with perovskite, which benefits for the charge transport in the IPSCs. The devices based on planar NiOx at 50 °C and low nickel precursor concentration achieved an enhanced efficiency from 16.14% to 18.17%. This work established an efficient CBD route to fabricate planar NiOx film for PSCs and paved the way for high performance PSCs with CBD-prepared hole transporting materials.