The long-term operational stability of perovskite solar cells is critically governed by the chemistry and electronic structure of buried interfaces between metal halide perovskites and charge transport layers. Developing scalable inorganic metal oxide contacts therefore requires a fundamental understanding of interface formation, defect generation, and energy level alignment during both perovskite growth and oxide deposition. Here, we present a systematic photoemission spectroscopy investigation of buried metal oxide/perovskite interfaces using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES), and photoluminescence imaging.

We first investigate the NiOₓ/perovskite interface in inverted (p-i-n) architectures and reveal that a redox reaction between NiOₓ and the perovskite leads to the formation of metallic nickel (Ni⁰), accompanied by interfacial defects and A-site cation deficiency. Surface functionalization with the MeO-2PACz organic molecule suppresses Ni⁰ formation, mitigates interfacial defects, and improves device performance [1]. We then examine the reverse configuration, where NiOₓ is deposited directly onto the perovskite by atomic layer deposition (ALD). Direct oxide growth induces chemical degradation at the buried interface, whereas an ultrathin PTAA interlayer efficiently suppresses precursor-induced reactions and improves device stability [2].

Extending this approach to ALD-grown SnO₂ electron transport layers, we show that direct deposition of SnO₂ induces interfacial defect formation and an electron extraction barrier resulting from chemical reactions between the ALD precursor and the perovskite surface. Introducing an ultrathin PCBM interlayer effectively suppresses these reactions, demonstrating a general strategy for protecting perovskite surfaces during oxide deposition [3].

Building on these findings, we establish a general design principle by comparing wide-bandgap formamidinium- and cesium-based perovskites exposed to oxide deposition by both ALD and pulsed laser deposition (PLD). While formamidinium-based perovskites undergo pronounced chemical degradation, cesium-based compositions exhibit remarkable chemical robustness and favorable electronic interface formation. Together, these results provide unified design rules for engineering chemically stable and electronically optimized metal oxide/perovskite interfaces, enabling scalable fabrication of durable, high-performance perovskite solar cells.