Effect of Annealing Treatment on Optical and Electrical Properties of PCDTBT:Graphene Hybrid Structure for Photovoltaic Application

Abstract

Indium tin oxide (ITO)/poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT):graphene/Al structures have been elaborated. By applying a specific elaboration method, we succeeded in dispersing expandable graphene oxide in organic solvent (N,N-dimethylformamide, DMF) to obtain graphene oxide and insert it into a PCDTBT matrix. The effect of annealing treatment of PCDTBT:graphene films on the optical and electrical properties were studied. The obtained results showed a remarkable effect of the annealing treatment on the optoelectronic properties. The ultraviolet–visible (UV–Vis) spectra showed that the light harvesting was increased and the orderly stacking of the polymer chains was enhanced. The photoluminescence results showed a red-shift of about 10 nm in case of heat treatment at 150°C, related to an increase of the conjugation length of the polymer chains. The electrical parameters, such as the series resistance (Rs), ideality factor (n), and barrier height (ϕb), were calculated. We found that thermal annealing reduced both the series resistance Rs and barrier height value ϕb, significantly. These results indicate that annealing treatment improves the transport phenomenon in the active layer. In addition, the Log(J)–Log(V) curves suggested that the charge transport is governed by a space-charge-limited mechanism current. The effective carrier mobility (μeff) was on the order of 10−5 cm2/V.