Thermal Stability and Performance Enhancement of Perovskite Solar Cells through Oxalic Acid-Induced Perovskite Formation

Achieving long-term stability along with high power conversion efficiency (PCE) is the biggest obstacle for the pursuit of organic-inorganic perovskite solar cells (PSCs) toward commercialization. Herein, we demonstrate additive assisted perovskite crystal growth as an effective strategy to improve both power conversion efficiency and thermal stability of methylammonium lead triiodide (MAPbI₃) perovskite solar cells. For this, oxalic acid (OA) with two bifacial carboxylic acid groups was employed as an additive into the perovskite precursor solution, which facilitated modulating the crystallization process leading to increase in grain size, reduced grain boundaries and trap states. Subsequently, devices fabricated with the OA additive showed a power conversion efficiency of 17.12%, compared to the control device with 14.06%. Furthermore, enhanced thermal stability was achieved for the OA-modified PSCs compared to that of the pristine device. The device without the OA additive retained 14% of the initial PCE after only 9 h of heat treatment at 100 °C, whereas for the same condition, the OA-modified device retained 90% after 9 h and even 70% after 19 h. These observations suggest that OA-assisted morphological improvement of perovskite can offer an efficient approach to further improve the performance as well as stability of the PSCs.