Constructing Efficient Hole Transport Material through π-Conjunction Extension for Perovskite Solar Cell

Efficient hole transport and excellent film formation properties are essential for efficient hole transport materials (HTMs) in perovskite solar cells (PCSs). And, the π-conjugated system and the steric configuration of HTMs can affect charge-carrier mobility and film formation. So, it is feasible to develop efficient HTMs via optimizing the molecular configuration and enlarging the π-conjugation system. Herein, a low-cost spiro[fluorene-9,9′-xanthene] (SFX) core-based HTM, named SFX-DM-DPA, is designed and synthesized through molecular engineering of the efficient HTM SFX-DM by introducing extra 4,4′-dimethoxydiphenylamine units to enlarge the π-conjugation range and to further modulate the charge transport property. The resulting HTM demonstrates enhanced hole extraction/transport efficiency and desired film formation ability. PSCs based on SFX-DM-DPA yielded an impressive efficiency of 22.7%. These results confirmed the importance of precise structural adjustment of the π-conjugated range for developing low-cost and highly efficient HTMs.