Branched Fluorenylidene Derivatives with Low Ionization Potentials as Hole-Transporting Materials for Perovskite Solar Cells

A group of small-molecule hole-transporting materials(HTMs) thatare based on fluorenylidene fragments were synthesized and testedin perovskite solar cells (PSCs). The investigated compounds weresynthesized by a facile two-step synthesis, and their properties weremeasured using thermoanalytical, optoelectronic, and photovoltaicmethods. The champion PSC device that was doped with lithium bis(trifluoro-methane-sulfonyl)-imide(LiTFSI) reached a power conversion efficiency of 22.83%. The longevityof the PSC device with the best performing HTM, V1387, was evaluated in different conditions and compared to that of 2,2 & PRIME;,7,7 & PRIME;-tetrakis(N,N-di-p-methoxy-phenyl-amine)-9,9 & PRIME;-spiro-bifluorene(spiro-MeOTAD), showing improved stability. This work provides analternative HTM strategy for fabricating efficient and stable PSCs.