Electro-active nanofibers of a tetrathiafulvalene derivative with amide hydrogen bonds as a dopant-free hole transport material for perovskite solar cells

A tetrathiafulvalene derivative containing two amide units for intermolecular hydrogen bonds (Bis-amide-TTF) was found to form supramolecular assemblies, in which intermolecular TTF cores were stacked with each other. The electrical conductivity of Bis-amide-TTF-based film was 1.28×10^-5Scm^-1, which was greater than that of spiro-OMeTAD doped with t-butylpyridine and bis(trifluoromethane)sulfonimide lithium salt (8.37×10^-6Scm^-1). Bis-amide-TTF was applied as a hole transport material (HTM) for perovskite solar cells (PSCs). The Bis-amide-TTF film has a deeper HOMO level than that of spiro-OMeTAD, leading to an increased open-circuit voltage of the PSCs. The power conversion efficiency of 14.5% with a short-circuit current density (J_sc) of 19.8 mA cm⁻², an open-circuit voltage (V_oc) of 1.11 V, and a fill factor (FF) of 66% was achieved for PSCs fabricated with the dopant-free Bis-amide-TTF-based HTM, which was comparable to that obtained with spiro-OMeTAD with the dopants (15.5%).