Precursor Tuning for Post-treatment Free MAPbI3 Films for Efficient and Stable Perovskite Solar Cells

Perovskite Solar Cells (PSCs) gained attention by solar photovoltaic community owing to excellent optoelectronic properties, solution processability, low cost and competing efficiencies with established technologies. Methyl ammonium lead iodide (MAPbI3) is the most commonly used perovskite absorber layer in PSCs owing to its optimum bandgap, ease of phase stabilization and high performance. MAPbI3 based PSCs are known to best perform when the perovskite films are prepared by 1-step recipe followed by conventionally heat treating at 100 °C. Here we report a different precursor where such heat treatment is unwanted and is in fact detrimental in MAPbI3 absorber layer-based PSCs. MAPbI3 films are developed by liquefying their single crystal counterparts in methylamine gas. The obtained precursor from the single crystals is suitable for both lab scale as well as large scale depositions. Here we study its crystallization mechanism in lab-scale spin coating process. The precursor crystallized instantaneously during spin-coating itself without any post annealing step. Our results indicate that annealing of the films is detrimental to its morphological, structural and optical properties thus rendering it unsuitable for photovoltaic applications. The films without annealing have resulted in an efficiency greater than 13% while the annealed films have resulted in less than 2%.