A Scorpion–Type Dopant-Free Hole Transport Material for n-i-p Organic–Inorganic Hybrid Perovskite Solar Cells

It is significant to develop dopant-free hole transport materials (HTMs) to improve the long-term stability of n-i-p organic–inorganic hybrid perovskite solar cells (PSCs). In this work, two HTMs (DTTP-T and DTTP-D) based on dithienothiopyrrole (DTTP) core were synthesized to explore the effects of different substituents on the nitrogen atom on the properties of HTMs. Compared with anisole-substituted DTTP-D, triarylamine-substituted scorpion-type DTTP-T shows better matching energy level, stronger charge transfer and defect passivation ability. Therefore, the power conversion efficiency (PCE) of dopant-free DTTP-T-based n-i-p PSCs reaches 18.67 %, which is comparable to that of doped Spiro-OMeTAD (19.51 %). More encouragingly, the efficiency of DTTP-T-based devices remains above 80 % of its initial efficiency after 1728 h of storage in air, while the Spiro-OMeTAD-based devices could only maintain 600 h. This work provides a good reference for the development of dopant-free small molecular HTMs for efficient and stable PSCs.