Solution-Processed High Work Function n-type V ₂ O _{5– <i>x</i>} 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 (V 2 O 5-x ) has emerged as a potential anode buffer layer for perovskite solar cells (PSCs). Almost all works claim that the prepared V 2 O 5-x is a p-type semiconductor and, therefore, serves as a hole transport layer. In this work, we demonstrate water-soluble V 2 O 5-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 V 2 O 5-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 V 2 O 5-x HCL pushes the device’s reverse breakdown voltage to reaching |−31.77| V, far beyond that of the conventional NiO x -based device (about |−6| V). This work highlights facile water-soluble V 2 O 5-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.