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.

Graphical AbstractThe power conversion efficiency (PCE) of organic solar cells based on P3HT:PCBM blended layer was improved by inserting a discotic liquid crystal. The chemical structure of [2,3,6,7,10,11]-Hexabutoxytriphenylene (HAT4) is shown in (a). Device structure with HAT4 is shown in (b). The current density–voltage characteristics under illumination is shown in (c). It can be seen that short-circuit current and fill factor were enhanced with the insertion of HAT4.Figure optionsDownload as PowerPoint slideHighlights
► PCE of OSCs is enhanced by inserting HAT4 between HTL and active layer.
► PEDOT:PSS, NiO and MoO3 were used as HTL in OSCs, respectively.
► HAT4 molecules change from the discotic phase to column phase after annealing.
► Alignment in columnar phases can provide an efficient pathway for carriers.
► Both JSC and FF were increased without VOC sacrifice.