Efficiency improvement in organic solar cells by inserting a discotic liquid crystal

In this paper, we reported a simple method to increase the power conversion efficiencies (PCEs) of solar cells based on poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester derivatives blended active layer. The approach includes insertion of a discotic liquid crystal [2,3,6,7,10,11]-Hexabutoxytriphenylene (HAT4) at the interface between the active layer and a hole transporting layer. HAT4 molecules distribute in the active layer to form a more efficient pass way for carriers leading to improve the charge mobility. The experiments also included different hole transporting layers (HTLs) (PEDOT:PSS, MoO3 and NiO) deposited on fluorine-tin oxide substrates, respectively. The results showed that both short-circuit current (JSC) and fill factor (FF) were increased without open-circuit voltage sacrifice. Maximum 43% increase in PCE with the insertion of HAT4 for three kinds of HTLs was obtained in the devices compared with that of the reference ones. The mechanisms behind JSC and FF increase are discussed.