Branched Methoxydiphenylamine-Substituted Carbazole Derivatives for Efficient Perovskite Solar Cells: Bigger Is Not Always Better

A set of novel branched molecules bearing a different number of 3,6-bis(4,4'-dimethoxydiphenylamino)carbazole-based (CzOMeDPA) periphery arms linked together by aliphatic chains have been developed, and their performance has been tested in perovskite solar cells (PSCs). Electrical and photovoltaic properties have been evaluated with respect to the number of Cz-OMeDPA moieties and the nature of the linking aliphatic chain. The isolated compounds possess sufficient thermal stability and are amorphous having high glass-transition temperatures (>120 degrees C) minimizing the risk of direct layer crystallization. The highest hole-drift mobility of mu(0) = 3.1 x 10(-5) cm(2) V-1 s(-1) is comparable to that of the reference standard spiro-OMeTAD (4.1 x 10(-5) cm(2) V-1 s(-1)) under identical conditions. Finally, PSCs employing two new HTMs (2CzOMeDPA and 3Cz-OMeDPA-OH) bearing two and three substituted carbazole chromophores, linked by an aliphatic chain, show a performance of around 20%, which is on par with devices using spiroOMeTAD and demonstrates slightly enhanced device stability.