Wavelength-Switchable Surface Photovoltage Polarity in Quasi-2D Perovskite Heterojunctions Mediated by Exciton Confinement

Abstract

Abstract Strong excitonic confinement in quasi-2D Ruddlesden–Popper perovskites gives rise to distinct photophysical behavior compared with their 3D analogues, yet how this confinement governs surface and interfacial photovoltage formation remains unresolved. We show that quasi-2D (PEA)2MA2Pb3I10 perovskite generates a surface photovoltage nearly an order of magnitude larger than that of 3D MAPbI3 perovskite, and exhibits an unexpected wavelength-dependent reversal of SPV polarity in quasi-2D (PEA)2MA2Pb3I10/TiO2 heterojunction from negative to positive as the excitation wavelength increases. This bidirectional response arises from a competition between two spatially distinct charge-separation channels, namely surface separation driven by the enhanced built-in field of polar PEA+ spacer cations and interfacial electron transfer at the buried TiO2 contact activated by deeper-penetrating photons. The quasi-2D lattice preserves this depth selectivity by strongly limiting out-of-plane exciton transport. Leveraging this mechanism, we demonstrate a proof-of-concept artificial visual system in which blue-violet and red light generate opposite photovoltage signals, encoding cancellation and execution commands within a single device. Our results identify exciton-mediated interfacial photovoltage engineering as a design principle for wavelength-programmable quasi-2D optoelectronics.