One-Pot Synthesis of Tetraarylpyrrolo3, 2-bpyrrole Dopant-Free Hole-Transport Materials for Inverted Perovskite Solar Cells

Four organic small-molecule hole transport materials ( D41 , D42 , D43 and D44 ) of tetraarylpyrrolo3, 2-bpyrroles were prepared. They can be used without doping in the manufacture of the inverted planar perovskite solar cells. Tetraarylpyrrolo3, 2-bpyrroles are accessible for one-pot synthesis. D42 , D43 and D44 possess acceptor- \pi -donor- \pi -acceptor structure, on which the aryl bearing substitutes of cyan, fluorine and trifluoromethyl, respectively. Instead, the aryl moiety of D41 is in presence of methyl with a donor- \pi -donor- \pi -donor structure. The different substitutes significantly affected their molecular surface charge distribution and thin-film morphology, attributing to the electron-rich properties of fused pyrrole ring. The size of perovskite crystalline growth particles is affected by different molecular structures, and the electron-withdrawing cyan group of D42 is most conducive to the formation of large perovskite grains. The D42 fabricated devices with power conversion efficiency of 17.3% and retained 55% of the initial photoelectric conversion efficiency after 22 days in dark condition. The pyrrolo3, 2-bpyrrole is efficient electron-donating moiety for hole transporting materials to form good substrate in producing perovskite thin film.