Insights into Perovskite Film Formation Using the Hybrid Evaporation/Spin-Coating Route: An In Situ XRD Study

The hybrid evaporation/spin-coating route has been widelyusedfor fabrication of highly efficient fully textured perovskite silicontandem solar cells and is a promising route for upscaling. Nevertheless,fundamental aspects of the fabrication process such as the kineticsof perovskite crystallization and the influence of the environmentalconditions remain uncertain. In this work, we investigate the individualstages of tandem-relevant 1.66 eV bandgap perovskite formation andmap the structural evolution from the precursor to the perovskitephase until the degradation phase. We find that the kinetics of thesetransitions can be tuned by varying the humidity or the temperatureduring the annealing treatment. Specifically, increasing the relativehumidity up to 50% elevates the reaction rate and results in improvedperovskite quality. This is directly reflected in the solar cell powerconversion efficiency with a 3%(abs) increment on average.While high annealing temperatures are found to promote large grainsize growth and enhanced crystallinity, we observe that above 150 degrees C the remnant PbI2 precursor compromises film quality.Furthermore, the perovskite formation kinetics is fitted using theJohnson-Mehl-Avrami-Kolmogorov model. The Avramiconstant is found in the range 0.66-0.87, indicating a diffusion-controlledone-dimensional growth process with an associated activation energyof 54.49 kJ/mol. Using in situ XRD, this work gives insights on keyprocess parameters to ensure reproducible synthesis of high-qualityperovskite films.