Perovskite is an emerging material for high performance solar cell application with low-cost solution-processable fabrication. As an ink, perovskite composition can be easily modified to create semi-transparent solar cells for window replacement. To enable scalable large-scale production, the spray process is one of the major candidates. In this work, we developed sequential spray deposition (SSD) to create double layer absorbers from different dimensional perovskites. SSD, for the first time, achieves layer-by-layer deposition of different perovskite materials for stacked architecture. To demonstrate the benefits, we spray-coated lower dimension, more stable perovskite onto high performance yet sensitive 3D semi-transparent perovskite. SSD performed under a humid environment (40 - 50% RH) brings about better film stability and retains good performance of 3D perovskite. Sequential spray deposition opens new routes for various stacking designs and large-scale production under economical ambient conditions.

Phase stability remains a critical bottleneck hindering the use of CsPbI 3 perovskites, which prefer to take on a nonperovskite, "yellow" phase at room temperature. The desired "black" phase perovskite, suitable for photovoltaic applications, can be obtained at elevated temperatures but readily reverts to the yellow phase under humid conditions and room temperature. B-site doping has shown some promise in improving the phase stability of perovskite nanocrystals; however, incorporating a sufficient amount of a single dopant into the perovskite lattice remains challenging.Here we report a dual-dopant strategy, where modest quantities of two divalent cations (Ca 2+ and Mn 2+ ) were simultaneously introduced in the fabrication of CsPbI 3 films to circumvent the need to introduce a single dopant in high quantities. DFT is used to uncover the importance of dopant-based stereoelectronic effects in phase stabilization. The CaMn dual-doped films can retain the black phase for up to 16 days at room temperature and 40−60 %RH; the mono-substituted and non-substituted analogues reverted to the yellow phase in seconds under the same conditions, demonstrating the ability of dual doping to improve optoelectronic materials' durability where a single dopant fails.

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