Electrochemical approach for preparing conformal methylammonium lead iodide layer

Monolithic perovskite/Si tandem solar cells have attracted particular interest because of the potential to achieve high power conversion efficiencies. However, tandem cells require the use of textured Si substrates for efficient light harvesting, and conformal deposition of the perovskite absorption layer on textured Si substrates remains challenging. Here, we introduce a process to prepare a conformal methylammonium lead iodide (MAPbI3) film on the various substrates regardless of their morphologies via the electrodeposition followed by vapor reaction. First, PbO2 films were electrodeposited on the planar indium tin oxide/NiO substrates in aqueous electrolyte, with their thickness and grain size controlled by adjusting the potential and reaction time. XPS and XRD analyses confirmed that the PbO2 film was fully reduced to PbO by annealing under a reducing atmosphere. Finally, the PbO films were converted into conformal MAPbI3 via MAI vapor reaction for 25 min at 180 °C. We also demonstrated that the PbO2 films could be evenly deposited on textured Si/ITO substrates using pulsed electrodeposition and were then converted into conformal MAPbI3 using the same vapor reaction process. The proposed approach thus provides a novel route for the preparation of high-quality perovskite films on both planar and textured substrates. Keywords: Electrochemical deposition, Thermal vapor reaction, Kinetics, Perovskite