Sequentially Evaporated Wide Bandgap Perovskite Absorber for Large-Area and Reproducible Fabrication of Solar Cells

Abstract

Herein, we perform sequential deposition of the organic and inorganic sub-components evaporated from point sources, followed by thermal conversion to yield wide bandgap perovskite films for the application in perovskite/silicon tandem cells. In our approach, uniform formamidinium iodide (FAI) layers with varying thicknesses are first deposited with rotating substrate. We next co-evaporate the inorganic precursors PbI₂, PbBr₂, and CsI onto the FAI layer in a static mode, without substrate rotation, leading to thickness gradients across the substrate, known from single-layer characterization. To promote conversion to α-phase perovskite, another uniform FAI layer is deposited on top, sandwiching the inorganic precursor layer stack. After thermal conversion, we obtain controlled compositional variations of the perovskite layer. Using spatially resolved characterization techniques, the most suitable composition, hence, evaporation rates for the individual inorganic precursors and the best thickness of the FAI sublayer are identified in a time-efficient manner. As a result, an optimized average implied open-circuit voltage, iV_OC, of about 1230 mV and optical bandgap of 1.70 eV, very uniformly distributed over a half M6 wafer area, were achieved for the absorbers when deposited on a self-assembled monolayer. Without any perovskite surface passivation or additional treatment, single-junction devices with an average fill factor of 70% (65%) in reverse (forward) light current–voltage scan and V_OC of 1075 mV were achieved across several batches. Integrating this absorber in tandem cells with a random-pyramid textured bottom-cell led to preliminary cells with efficiencies up to 24%.