Detrimental Effect of Unreacted PbI<sub>2</sub> on the Long-Term Stability of Perovskite Solar Cells.

Tumen-Ulzii, Ganbaatar; Qin, Chuanjiang; Klotz, Dino; Leyden, Matthew R; Wang, Pangpang; Auffray, Morgan; Fujihara, Takashi; Matsushima, Toshinori et al. · Adv Mater · 2020

basic_science · Level V

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Abstract

Excess/unreacted lead iodide (PbI<sub>2</sub> ) has been commonly used in perovskite films for the state-of-the-art solar cell applications. However, an understanding of intrinsic degradation mechanisms of perovskite solar cells (PSCs) containing unreacted PbI<sub>2</sub> has been still insufficient and, therefore, needs to be clarified for better operational durability. Here, it is shown that degradation of PSCs is hastened by unreacted PbI<sub>2</sub> crystals under continuous light illumination. Unreacted PbI<sub>2</sub> undergoes photodecomposition under illumination, resulting in the formation of lead and iodine in films. Thus, this photodecomposition of PbI<sub>2</sub> is one of the main reasons for accelerated device degradation. Therefore, this work reveals that carefully controlling the formation of unreacted PbI<sub>2</sub> crystals in perovskite films is very important to improve device operational stability for diverse opto-electronic applications in the future.