Electrochemical Modulation of Hole Extraction in NiO/Perovskite Bilayers

Abstract Charge extraction (or injection) at the transport layer/lead halide perovskite interface is a decisive process in determining the efficiency of optoelectronic devices. To elucidate the influence of band offsets on the hole transfer process, a series of perovskite thin films with systematically tuned valence band positions (FA 0.83 Cs 0.17 Pb(I x Br 1‐x ) 3 ) are fabricated and deposited on mesoporous NiO hole transport layers. In this work, transient absorption spectroscopy is performed to study the kinetics of hole transfer through the NiO/perovskite interface. It is revealed that a larger valence band offset is beneficial for hole extraction. To understand how hole depletion/accumulation influences the hole extraction process, in situ transient spectroelectrochemical measurements are also employed. These results highlight that, at negative applied electrochemical biases, an acceleration of the hole transfer process is found for different perovskite compositions. A more pronounced increase in the hole extraction rate can be tied to a larger valence band offset at the NiO/perovskite interface. These results provide a better understanding of the charge extraction process at NiO/perovskite interfaces, enabling more rational design of these systems.