Thermal stability of perovskite solar cells incorporated with spiro-OMeTAD and an ionic liquid dopant

Abstract

Perovskite solar cells (PSCs) have garnered attention as novel photovoltaic devices due to their cost-effectiveness, lightweight nature, and high photoconversion efficiency. To facilitate their commercialization, developing PSCs with enhanced environmental stability with respect to thermal and light resilience, making them suitable for outdoor applications, is imperative. However, despite ongoing research and development efforts, PSCs exhibit stability issues, including thermal- and light-induced degradation. In conventional PSCs, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as a dopant is essential to enhance the conductivity of the hole transport layer (HTL), such as 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD). However, LiTSFI incorporation into spiro-OMeTAD renders it unsuitable for applications requiring thermal stability owing to the Li+ diffusion within the PSCs. Since LiTFSI is a hydrophilic salt, we utilized organic TFSI salts to improve PSC thermal stability. By optimizing HTL using organic TFSI dopants, we achieved a remarkable two-fold enhancement in thermal stability compared to non-optimized PSCs.