Solution-Processed High Work Function n-type V2O5–x for Inverted Perovskite Solar Cells with Enhanced Photovoltaic Performance and Reverse Bias Stability

Recently, with the advantage of a multivalent state, facile, and low-temperature preparation method, vanadium oxide (V2O5-x) has emerged as a potential anode buffer layer for perovskite solar cells (PSCs). Almost all works claim that the prepared V2O5-x is a p-type semiconductor and, therefore, serves as a hole transport layer. In this work, we demonstrate water-soluble V2O5-x exhibiting n-type conductivity, which can still serve as an effective hole collection layer (HCL) in PSCs. Comprehensive characterizations and DFT calculations reveal that V2O5-x is an n-type semiconductor with a high work function (WF). Further coupled with self-assembled monolayer, it can simultaneously optimize the front interface band bending via enhancing the ITO electrode’s WF and reduce interface defect density, thereby facilitating carrier collection and suppressing nonradiative recombination, leading to an inverted PSC with a highest power conversion efficiency of 23.5% and underscoring the importance of strategic interface engineering rather than only relying on a conventional p-type conduction paradigm. Moreover, the device exhibits excellent reverse bias stability. The high-WF n-type V2O5-x HCL pushes the device’s reverse breakdown voltage to reaching |−31.77| V, far beyond that of the conventional NiOx-based device (about |−6| V). This work highlights facile water-soluble V2O5-x-based PSCs that demonstrate a device operating mechanism and high reverse bias stability, which provides a feasible route to achieving efficient and stable PSCs.