[20a-G202-1~10] 12.5 Organic solar cells

[20a-G202-3] Stable Perovskite Solar Cells Using Lithium-Ion Endohedral Fullerene (Li⁺@C₆₀)
as Both Dopant and Anti-Oxidant

〇Yutaka Matsuo^1,2, Il Jeon¹, Hiroshi Ueno³, Seungju Seo¹, Shigeo Maruyama^1,4 (1.The Univ. of Tokyo, 2.USTC, 3.Northeast Normal Univ., 4.AIST)

Keywords:Perovskite solar cells, Lithium-encapsulated fullerene, Anti-Oxidant

Lead halide perovskite solar cells (PSCs) have drawn great attention as the promising solar energy source in recent years. Their certified power conversion efficiencies (PCEs) now reach more than 20%. Despite high PCE, low stability of PSCs has been the most serious drawback, which is in dire need of resolution. In this work, lithium-ion-encapsulated fullerene bis(trifluoromethanesulfonyl)imide salt ([Li⁺@C₆₀]TFSI⁻) was used in PSCs as both dopant for spiro-MeOTAD and anti-oxidant instead of Li⁺TFSI⁻. C₆₀ encapsulating Li⁺ changed the hydrophilic alkali salt to a hydrophobic species. Also, spiro-MeOTAD mixed with [Li⁺@C₆₀]TFSI⁻ produced cationic salt spiro-MeOTAD^•+TFSI⁻ and neutral Li⁺@C₆₀^•− by electron transfer from spiro-MeOTAD to Li⁺@C₆₀. While spiro-MeOTAD^•+TFSI⁻ functioned as an effective hole transporting material Li⁺@C₆₀^•− functioned as an antioxidant, reacting with any intruding oxygen and moisture. spiro-MeOTAD^•+TFSI⁻ required no chemical additives nor oxidation as it was technically pre-oxidized spiro-MeOTAD. By preventing unnecessary oxidation in the device system, [Li⁺@C₆₀]TFSI⁻-used devices showed approximately 10 times higher stability than the conventional Li⁺TFSI⁻-used devices.