MeO-2PACz-Mediated Interfacial Engineering for Strain Regulation in Efficient Narrow-Bandgap Sn-Pb Perovskite Solar Cells

Compositional engineered narrow-bandgap (NBG) Sn-Pb perovskites with an intrinsic bandgap of 1.2-1.3 eV have emerged as promising photovoltaic materials, holding tremendous application prospects in tandem solar cells, near-infrared photodetection and imaging, as well as building-integrated photovoltaics (BIPV). However, their practical applications are severely hampered by severe Sn²⁺ oxidation, mismatched crystallization and large interfacial compressive strain between perovskite and hole transport layer. Herein, we adopt co-additives to fundamentally suppress Sn2+ oxidation, and further construct a MeO-2PACz self-assembled monolayer (SAM) buried interface to relieve bottom interfacial compressive strain of perovskite films. The SAM buffer layer mitigates lattice and thermal expansion mismatch-induced strain, reduces lattice distortion and interfacial defects, and optimizes interfacial energy level alignment simultaneously. Benefiting from the above interfacial engineering, the oxidation of Sn2+ in NBG Sn-Pb perovskite absorbers is remarkably inhibited. As a result, the optimized Sn-Pb perovskite devices deliver a power conversion efficiency (PCE) of 20.50%. In addition, the unencapsulated devices with synergistic modification of additive engineering and MeO-2PACz interfacial treatment exhibit exceptional long-term durability. Specifically, the devices maintain 95% of the original efficiency after 1000 h of ambient exposure, and retain 93% of their initial efficiency after 20 h thermal aging at 85 °C in a nitrogen atmosphere.