Two cyclohexanofullerenes used as electron transport materials in perovskite solar cells

Two fullerene C-60 derivatives, 2-(3-ethoxycarbonylpropyloxy)-(5,8)-dihydronaphthyl-(6,7)-[6,6]-C-60 (EDNC) and 2-benzyloxy-(5,8)-dihydronaphthyl-(6,7)-[6,6]-C-60 (BDNC), are introduced into p-i-n type planar heterojunction perovskite solar cells as electron transport materials (ETMs) to investigate electrochemical, charge-transporting, and film-forming properties of fullerene ETMs and the resulting photovoltaic performance in comparison with [6,6]-phenyl-C-61-butyric acid methyl ester (PC61BM). Due to better surface morphology, the EDNC-involving device shows better performance (12.64%) than that of BDNC-based device (7.36%) despite of their similar LUMO energy level, electron mobility, optical properties, and electrochemical properties. Higher power conversion efficiency (PCE) of 15.04% is achieved using PC61BM as the ETM, the electronic mobility of PC61BM is approximately one order of magnitude higher than that of EDNC, which leads to slightly higher short-circuit current density and fill factor for PC61BM-based device. This work demonstrates that factors such as electron mobility and surface morphology should be envisaged in searching for fullerene derivatives as efficient ETM in perovskite solar cells. (C) 2017 Published by Elsevier B.V.