Improving the Performance of Perovskite Solar Cells Fabricated in Ambient Atmosphere

Abstract

The metal halide perovskites have proven their potential in being the active absorption layer for the third-generation perovskite solar cells (PSCs). Their reported power conversion efficiency (PCE) is one of the fastest growths in the last decade, closing in towards the Shockley-Queisser limit and the silicon solar cell’s highest recorded PCE. This was possible by exploiting properties, like tunable band gap, excellent photon absorption, and long carrier diffusion lengths. One of the possible ways to further improve the performance of the PSCs is by fabricating high-quality, defect-free perovskite films and optimizing the PSC’s architecture accordingly. Ambient fabrication (Avg. 45% relative humidity) of PSCs usually causes non-uniform morphology and unequal crystal growth of the perovskite thin film leading to bad performance of the PSC. The motivation for this research is to fabricate high-efficiency metal halide perovskite solar cells with good optoelectronic and photovoltaic properties in complete ambient conditions i.e., without the use of an inert gas environment/glove box. Fabrication in such an environment leads to the formation of larger grains and defects. Hence, optimizing the fabrication process to minimize the defects, results in uniform deposition of perovskite active layer with larger grain size, which will aid in faster carrier transportation. By fine-tuning the growth conditions of every layer in the PSC and optimizing their fabrication variables, one can achieve improved performance from a PSC. Hence, choosing the most effective source materials and deposition conditions that work in ambient conditions for both electron transport layer (ETL) and hole transport layer (HTL) and optimizing the thin films for best extraction and transportation of charge carriers while also blocking the opposite charge carrier is essential. We took measures to improve the quality of the perovskite active layer by using mixed anti-solvent to increase the grain size and depositing a passivation layer on perovskite thin film before the HTL to lower the surface defects. Therefore, a synergistic effect from various individual optimizations done at each layer and interface level was anticipated, which successfully improved the PCE of our PSCs fabricated in ambient conditions from around 7% to above 15%.