Anionic engineering of a p-dopant enables efficient and stable perovskite solar cells

Abstract

Lithium bis(trifluoromethane)sulfonimide (Li-TFSI) is extensively employed as a p-type dopant to enhance the conductivity of hole-transporting materials (HTMs) in n–i–p perovskite solar cells (PSCs). Despite its effectiveness, the hygroscopic and migratory nature of Li-TFSI compromise the long-term stability of PSCs. Herein, a new p-type dopant, namely, lithium tetrakis(pentafluorophenyl)borate (Li-BCF), was constructed for use in a poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA)-based PSC by replacing the anion unit TFSI⁻ of Li-TFSI with the fluorinated boric acid anion BCF⁻. It was found that the BCF⁻ anion has stronger interactions with Li⁺ and PTAA˙⁺ compared with the TFSI⁻ anion, resulting in weakened moisture absorption and migration of Li⁺ as well as improved doping stability of the PTAA:Li-BCF combination when subjected to elevated temperatures up to 85 °C. With this anionic engineering, a fabricated Li-BCF-doped PTAA-based device achieved improved efficiency and retained 95% of its initial power conversion efficiency during 1000 h of one-sun operation at its maximum power point (ISOS-L-1), yielding up to a 12-fold increase in T₈₀ operational lifetime. Our findings provide valuable insights for the future design of p-type dopants and for their optimized use in photovoltaic applications.