One-pot synthesis of tetraarylpyrrolo[3,2-b]pyrrole dopant-free hole-transport materials for inverted perovskite solar cells

Four organic small-molecule hole transport materials (D41, D42, D43 and D44) of tetraarylpyrrolo[3,2-b]pyrroles were prepared. They can be used without doping in the manufacture of the inverted planar perovskite solar cells. Tetraarylpyrrolo[3,2-b]pyrroles are accessible for one-pot synthesis. D42, D43 and D44 possess acceptor-π-donor-π-acceptor structure, on where the aryl bearing substitutes of cyan, fluorine and trifluoromethyl, respectively. Instead, the aryl moiety of D41 is in presence of methyl with a donor-π-donor-π-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 17.3% and retained 55% of the initial PCE after 22 days in dark condition. The pyrrolo[3,2-b]pyrrole are efficient electron-donating moiety for hole transporting materials to form good substrate in producing perovskite thin film.