A three-dimensional multi-chromophore naphthalene diimide acceptor for polymer bulk heterojunction solar cells

摘要

Non-fullerene acceptors are proving to be effective for high efficiency polymer bulk heterojunction solar cells. We report the synthesis and properties of a three-dimensional naphthalene diimide-based acceptor where four dithienylnaphthalene moieties are attached to a central tetraphenylethylene unit. In spite of the material being designed as an electron acceptor it was found to have similar and good hole and electron mobilities of 1.5 x 10(-4) and 1.8 x 10(-4) cm(2)/Vs, respectively. When blended with PTB7-Th, which had previously been used with other three-dimensional acceptors, at a weight ratio of 1:1 the hole mobility was found to increase slightly but the electron mobility decreased such that there was an imbalance of two orders of magnitude. The blend with a 1:1 donor:acceptor weight ratio was found to give devices with the best power conversion efficiency of 3.0 Wo in an inverted device architecture, which is amongst the best for non-polymeric naphthalene diimide acceptors. A combination of transient absorption and intensity dependent measurements, along with the charge mobility results indicated that while exciton separation was rapid, the performance of the devices was limited by recombination processes that decreased the extraction of the photogenerated charges.