Electrodeposition was investigated as a substitute technology to deposit the perovskite active layers in large area solar cells. This method involves growing perovskite crystals from a metal or metal oxide layer that had first been electroplated. A schematic representation of the electrodeposition process and subsequent conversion steps is shown in Figure 1. This technology offers a low-cost approach that produces smooth and uniform layers over large areas. Additionally, the process is conducted under ambient conditions, avoiding the need for a glove box. It’s also environmentally friendly, as no toxic solvents are required to stabilize or enhance the morphology of the layers. Finally, the electrodeposition is easy to scale up and proven to improve the interfaces (and thereby the charge transfer) between the layers.

In this study we propose to try and use the electrodeposition protocol developed in the laboratory [1,2,3,4] with the addition of bismuth as a “doping agent” of the traditional MAPbI₃ perovskite.  Bismuth was introduced into the conversion bath as a precursor, partially substituting lead.  This approach was motivated by efforts to reduce lead and previous evidence [5,6] suggesting that bismuth doping improves the solar cells stability. However, the former studies focused on cells processed via spin coating or drop casting, not electrodeposition.  We investigated how varying the MAI:BiI₃ ratio in the conversion bath affected  the properties of the electrodeposited devices. Even at very low ratios, the microstructure, optical properties, chemical properties, bandgap energy, crystallinity, and stability of the perovskite were deeply impacted by the presence of the Bi.  It also strongly affects the photovoltaic performance of the electrodeposited solar cells. Moreover, these parameters not only depend on the amount of Bi precursor in the bath, but also on the conversion time, suggesting a complex formation of the structures.

In conclusion, while the addition of bismuth in MAPI perovskites is generally associated with reduced PCE, our study demonstrates that it can also offer interesting advantages. We demonstrate that with a specific amount of bismuth, the PCE remains comparable to that of MAPbI₃, but with a stability significantly enhanced.  A key result is the experimental evidence that Bi-doped photovoltaic cells remain functional even after 1000 hours of aging at 90% relative humidity and 30°C, even without any encapsulation.