Thienoimidazole-pyridine based small molecule hole transport materials for dopant-free, efficient inverted perovskite solar cells

Abstract

Small-molecule hole-transporting materials (HTMs) containing heteroatoms provide enhanced interface contact and complete passivation effects, which increase the performance of perovskite solar cells (PSC). In this study, we present the synthesis and analysis of two small molecule HTMs, CYH20 and CYH23, based on a novel thienoimidazole-pyridine acceptor core for dopant-free and efficient inverted (p–i–n) PSCs. The two HTMs are structurally similar, except for the end units, 4-(1-cyanovinyl)benzonitrile (acceptor) and 2,2-bis(4-methoxyphenyl)vinyl (donor) moieties. As a result, CYH20 is classed as a donor–acceptor–acceptor (D–A–A) HTM and CYH23 as a donor–acceptor–donor (D–A–D) HTM. These new HTMs have favorable optoelectronic and thermal properties and suitable morphologies, as demonstrated by scanning electron microscopy, photoluminescence (PL) time-resolved PL, and space charge limited current studies. Among both, the D–A–D configured HTM CYH23-based PSC has a high open-circuit voltage of 1.08 V and a high short circuit current density of 21.78 mA cm⁻², resulting in the highest power conversion efficiency of 18.77%. The superior performance of CYH23 over CYH20 (17.14%) is attributed to its excellent morphology and charge transfer properties.