Composition-Dependent Interfacial Energetics in p – i – n Perovskite Solar Cells

Compositional engineering offers a direct route to tuning the absorber band structure and interfacial energy alignment in perovskite solar cells (PSCs). We systematically varied the formamidinium (FA)/methylammonium (MA) and I/Br ratios in Cs0.05(FAxMA1–x)0.95Pb(IxBr1–x)3 perovskites to examine how composition governs charge extraction, interfacial recombination, and photovoltaic performance in p–i–n-structured devices. Increasing the FA and I content gradually narrowed the optical bandgap through the progressive shift in the perovskite band edges, which in turn modified the band offset at the interfaces with both p- and n-type selective contacts. The resultant photovoltaic performance of p–i–n devices (MeO-2PACz/perovskite/C60) was monitored closely with composition across the series, reaching an optimum at x = 0.93. Impedance spectroscopy confirmed that carrier extraction efficiency and recombination dynamics are governed by the composition-dependent interfacial band alignment and defect density.