Abstract
Hole-transport materials are a crucial element influencing the efficiency, hysteresis, and stability of perovskite solar cells (PSCs). Current state-of-the-art hole-transport materials require additional oxidizing dopants to achieve sufficient hole-transport properties; however, these dopants are environmentally harmful while also deteriorating the stability of PSCs. The development of high-performance dopant-free hole-transport materials is an important goal in the field of PSCs. In this work, we developed novel conjugated small-molecule based dopant-free hole-transport materials for PSCs containing di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole (DBTP) as a core unit. These small molecule hole-transport materials achieved higher hole mobility and interfacial charge transfer rates than optimally doped spiro-OMeTAD, the current-state-of-the-art hole-transport material. A low-temperature PSC device using a dopant-free small molecule hole-transport material displayed a PCE of 18.09% with negligible hysteresis, higher than a device using doped spiro-OMeTAD (17.82%). Notably, the hydrophobic nature of our dopant-free small molecule hole-transport materials afforded excellent air-storage stability of low-temperature PSCs (81% retention after 33 days), whereas the doped spiro-OMeTAD based PSCs rapidly degraded under identical conditions (< 1% retention after 33 days).
High-performance dopant-free small molecule hole-transport-materials (SM-HTMs) for perovskite solar cells (PSCs) are developed. The SM-HTMs possess appropriate energy levels with sufficient hole mobility to function as efficient HTM for PSCs without additional dopants. A low-temperature PSC (L-PSC) device using a dopant-free SM-HTM displayed a PCE of 18.09% with high air-storage stability, which is superior to a device using doped spiro-OMeTAD. [Display omitted]
•Novel dopant-free hole-transport-materials for perovskite solar cells were developed.•The face-on orientation enabled sufficiently high hole mobility without dopants.•Low-temperature PSCs based on the dopant-free HTMs showed the efficiency of 18.09%.•The dopant-free HTMs acted as passivation layers, providing excellent air stability.