Synergistic film optimization and interfacial modification to boost the performance of wide-bandgap perovskite solar cells

Abstract

Wide-bandgap mixed-halide perovskites are promising for tandem solar cells but often face issues such as poor crystallinity, high non-radiative recombination, and voltage losses. In this work, we introduce a synergistic strategy that integrates lead thiocyanate (Pb(SCN)₂) as an additive and a quasi-2D perovskite (n ≥ 1) interlayer between the perovskite active layer and the electron transport layer (ETL) to simultaneously enhance the efficiency and operational stability of wide-bandgap perovskite solar cells. The incorporation of Pb(SCN)₂ promotes the formation of a superior perovskite film morphology by enlarging grain size and improving crystallinity. The excess lead iodide (PbI₂) generated from the additive was converted into a quasi-2D perovskite layer. This interfacial layer acts as a defect passivation layer. Moreover, the quasi-2D interlayer facilitates efficient charge extraction due to its favorable band alignment with the underlying perovskite absorber and adjacent ETL. These combined bulk and interfacial modifications result in a substantial boost in device performance, with the power conversion efficiency (PCE) increasing from 13.81% to 19.34%, achieving an open-circuit voltage of 1.23 V, short-circuit current density of 19.36 mA cm⁻², and fill factor of 81%. Furthermore, the devices exhibit good operational stability, retaining over 90% of their initial efficiency after 200 hours of continuous 1-sun illumination in ambient conditions, highlighting the role of defect suppression in long-term operational stability.