Spiro-Phenylpyrazole-9,9″-Thioxanthene Analogues as Hole-Transporting Materials for Efficient Planar Perovskite Solar Cells

Abstract

Perovskite solar cells have emerged as a promising technique for low-cost, light weight, and highly efficient photovoltaics. However, they still largely rely on 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) to serve as hole-transporting materials (HTMs). Here, a series of HTMs with small molecular weight is designed, which are constructed on a spiro core involving phenylpyrazole and a second heteroaromatics, i.e., xanthene (O atom), thioxanthene (S atom), and acridine (N atom). Through varying from phenylpyrazole substituted xanthene (PPyra-XA), thioxanthene (PPyra-TXA), to acridine (PPyra-ACD), their optical and electrochemical properties, hole mobilities, and the photovoltaic performance are optimized. As a consequence, PPyra-TXA based device exhibits the highest power conversion efficiency (PCE) of 18.06%, outperforming that of Spiro-OMeTAD (16.15%), which could be attributed to the enhancement of hole mobility exerted by the thioxanthene. In addition, the dopant-free device shows PCE of 11.7%. These results open a new direction for designing spiro-HTMs by simple modification of chemical structures.