Publication date: 15th December 2025
Perovskite solar cells (PSCs) continue to push the boundaries of efficiency and manufacturability, and much of this progress hinges on the quality of charge-transport layers (CTLs) and their interfaces with the perovskite absorber. These buried junctions govern not only device performance but also play a decisive role in long-term stability. In particular, the introduction of SnO2 interlayers has led to significant enhancements in perovskite film stability1. Yet depositing SnO2 directly onto soft metal halide perovskite thin films remains a fundamental challenge, as unwanted interfacial reactions can degrade the underlying perovskite2. This issue remains underexplored for wide-bandgap, bromine-based perovskites, despite the technological relevance of compositions such as FAPbBr3 and CsPbBr3 for tandem photovoltaics, and their interactions with SnO2 CTLs are still poorly understood. Advanced deposition techniques, including atomic layer deposition (ALD) and pulsed laser deposition (PLD), offer precise control over film thickness and composition, yet both processes can introduce chemical and structural stresses when applied directly to the perovskite surface.
By employing a correlative multi-technique approach that integrates photoluminescence (PL) imaging with advanced photoemission spectroscopy methods—ultraviolet photoelectron spectroscopy (UPS) and hard X-ray photoelectron spectroscopy (HAXPES)—we elucidate how SnO2 deposited by ALD or PLD on FAPbBr3 and CsPbBr3 affects the interfacial electronic structure and non-radiative recombination as a result of film formation and deposition-induced damage.
Grazing-incidence X-ray diffraction (GIXRD) measurements confirm that the perovskite crystal structure remains largely intact following oxide deposition. PL imaging enables quantification of the bandgap (Eg) and quasi-Fermi level splitting (QFLS), revealing composition-dependent trends in optoelectronic behavior that arise from differences in interfacial dynamics associated with each deposition method.
Quantitative fitting of HAXPES spectra at different excitation energies uncovers the chemical origins of this contrasting behavior, showing that ALD and PLD induce distinct types of surface or near-interface modifications, with the extent and nature of these effects strongly dependent on the A-site cation chemistry.
Overall, the study reveals that the A-site composition of wide-bandgap perovskites governs their tolerance to oxide deposition processes and determines whether SnO2 acts as a benign passivation layer or as a source of interfacial degradation. These insights provide guiding principles for the design of oxide/perovskite interfaces optimized for wide-bandgap optoelectronic and tandem photovoltaic applications.
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