Publication date: 15th December 2025
Metal halide perovskites (MHPs) combine high absorption coefficients, low exciton binding energies, long carrier diffusion lengths, and balanced ambipolar transport, enabling high-efficiency, low-cost photovoltaic devices. Despite these advantages, device performance and operational stability are critically governed by the interfaces between the perovskite absorber and the charge transport layers (CTLs). Interfacial recombination, band alignment, and field-driven ionic redistribution remain insufficiently understood, largely due to the lack of spatially resolved operando characterization strategies.
In this work, we develop a novel approach to probe and optimize these interfaces by performing photoluminescence (PL) measurements under operando conditions, enabling direct investigation of the optoelectronic properties at the MHP/CTL interface.
Our study focuses on lateral heterojunction (LHJ) devices, which employ carrier-selective materials as back contacts and provide direct optical access to the active layer from the top [1,2]. Specifically, we investigate LHJ architectures incorporating NiOx and TiO2 as hole- and electron-selective contacts, respectively, interfaced with the triple-cation perovskite Cs0.05MA0.10FA0.85PbI3. Devices are subjected to cyclic measurements with incrementally increasing electric fields (from 0 to +V), including recovery intervals between bias steps to mitigate persistent field-induced effects. During these experiments, the evolution of the active layer at both interfaces is continuously monitored while recording current as a function of time.
From microscopically resolved spectral maps, we extract local bandgap variations and determine the quasi-Fermi level splitting (Δμ). Simultaneously, PL imaging reveals surface and bulk defects, as well as spatial inhomogeneities within the perovskite layer.
Under applied bias, we observe a clear increase in photocurrent, confirming efficient carrier extraction in the lateral configuration. Spatially resolved maps of Δμ and PL intensity reveal asymmetric behavior at the two interfaces, indicative of selective and efficient charge transfer. Moreover, progressively increasing the applied voltage leads to irreversible degradation at one interface, highlighting the critical role of field-induced interfacial processes in device stability.
Chiara Mello, Stefania Cacovich. and Philip Schulz acknowledge funding from the ANR under the EMAP project (ANR-23-CE50-0025). Chiara Mello thanks the Fondation de l’Ecole polytechnique for supporting her doctoral research with the "Theses Objectifs de Developpement Durable (ODD)” scholarship.
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