In-situ monitored chemical bath deposition of planar NiOx 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 SnO 2 , 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 NiO x film as the efficient hole transport layer for the inverted perovskite solar cells (IPSCs). The morphologies and semiconducting properties of the NiO x film can be adjusted by varying the concentration of [Ni(H 2 O) x (NH 3 ) 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 NiO x 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 NiO x 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 NiO x film for PSCs and paved the way for high performance PSCs with CBD-prepared hole transporting materials.