Spiro-Phenylpyrazole/Fluorene as Hole-Transporting Material for Perovskite Solar Cells.

Spiro-OMeTAD with symmetric spiro-bifluorene unit has dominated the investigation of hole-transporting material (HTM) for efficient perovskite solar cells (PSCs) despite of its low intrinsic hole conductivity and instability. In this study, we designed and synthesized three asymmetric spiro-phenylpyrazole/fluorene base HTMs, namely: WY-1, WY-2 and WY-3. They exhibit excellent electrochemical properties and hole conductivities. Moreover, the PSC based on WY-1 exhibits the highest power conversion efficiency (PCE) of 14.2%, which is comparable to the control device employing spiro-OMeTAD as HTM (14.8%). These results pave the way to further optimization of both molecular design and device performance of the spiro-based HTMs.