Enhancement on charge transfer properties of Cu12Sb4S13 quantum dots hole transport materials by surface ligand modulation in perovskite solar cells

Colloidal quantum dots (QDs) have been considered as novel hole transport materials (HTMs) for perovskite solar cells (PSCs). Optimizing the surface state of QDs can provide higher current density and better stability. In this work, the original ligand (oleylamine) on the surface of Cu12Sb4S13 QDs is first replaced with trimethylammonium hydroxide and then with 3-mercaptopropionic acid through a two-step process, which exhibits better optical property and higher quality. Meanwhile, pure short chain ligand (3-mercaptopropionic acid) capped Cu12Sb4S13 QDs can provide an excellent charge transfer pathway when used as a hole transport layer of perovskite solar cells. As a result, PSCs based on the Cu12Sb4S13 QDs HTMs prepared by a two-step ligand-exchange process exhibited higher current density than devices based on spiro-OMeTAD, which enhanced the photovoltaic conversion efficiency from 14.65% to 15.43%.