Hole-transport materials based on the terthienyl core unit for efficient perovskite solar cells

Thiophene and oligothiophenes have outstanding electronic properties, especially their electron-rich nature, which endows them with good interfacial contacts with perovskite layers, and hence makes them ideal building blocks for hole-transport materials (HTMs). In the current work, we successfully synthesized two novel HTMs with terthienyl (TTP) as the core structure and triphenylamine or 4,4 '-dimethoxydiphenylamine as the end-capping groups, and termed them THP-1 and THP-2, respectively. Compared with THP-2, THP-1 exhibited a more suitable energy level and appropriate three-dimensional molecular structure, leading to better optoelectronic properties for THP-1. After optimization, PSCs based on THP-1 as the HTM achieved a power conversion efficiency (PCE) of as high as 20.47%, much higher than that of THP-2 (17.16%), and comparable to that of the control device based on spiro-OMeTAD (20.28%). Furthermore, the THP-1-based device maintained 71.5% of its initial efficiency, while the THP-2-based device and control device maintained only, respectively, 22.3% and 43.3% of their initial efficiency values, after 840 h aging tests at room temperature and under 30-45% relative humidity conditions, indicative of the excellent stability of the THP-1-based device.