Preparation And Optical Properties Of Functionalized Reduced Graphene Oxide And Poly (3-hexylthiophene) Composite Films

Polymer solar cells (PSCs) have attracted considerable attention because oftheir usefulness in developing light weight, large ares, cost effective panels onflexible substrates by means of simple and low environment impact technologies.However, the power conversion efficiency of polymer solar cells is low. In orderto improve the performance of the polymer solar cells, the design and screeningof different active materials are needed. Graphene, which has uniquetwo-dimensional structure and excellent electrical properties, can form a largecontact interface with electron donor material, which can increase the diffusionrate of excitons and the mobility of carriers. What’s more, raw material forpreparation of graphene is of wide range and low cost, for easy preparation.Therefore, graphene is a promising electron acceptor material.The target of this paper is to develop graphene as a suitable electronacceptor material for polymer solar cells. In this paper, graphene oxide (GO)was prepared by Hummers method. The GO was reduced by hydrothermalmethod at180℃for different times (0,5and10h) to give three kinds ofreduced graphene oxide (0-RGO,5-RGO and10-RGO). Then the GO and RGO were reacted separately with phenyl isocyanate to obtain three kinds of solutionprocessable functionalized graphenes (SPFGO,5-SPFRGO and10-SPFRGO).The composite films were prepared with the functionalized graphene materialsas acceptor and P3HT as donor. The main conclusions are as follows:(1) GO was prepared by Hummers method and the morphology wasobserved by SEM and TEM, the structures of GO were analyzed by XRD, FT-IRand Raman. The results show that the prepared GO was of about3-5layers withplentiful oxygen-containing functional groups such as-COOH and C=O on itssurface, which provides the active sites for subsequent surface modificationreaction.(2) GO was reduced by hydrothermal method. The impact of reduction timewas studied. The RGO was functionally modified by phenyl isocyanate. Thestructure of RGO was observed by XRD, FT-IR, EA and Raman. Thermalstability and energy level were analyzed by TG and CV, respectively. The resultsshow that the number of oxygen-containing groups decreased significantly, thethermal stability of the RGO is increased, O/C ratio significantly decreased withthe extension of reduction time. The dispersibility of RGO in o-dichlorobenzenewas enhanced significantly after functionalization with phenyl isocyanate. Thefunctionalization RGO can be well dispersed in o-dichlorobenzene after700h.ΔE1and ΔE3between P3HT and acceptor materials (0-SPFRGO,5-SPFRGOand10-SPFRGO) are large than0.3eV, indicating the acceptor materials are allsuitable for use in polymer solar cell. (3) P3HT:SPFRGO composite film was prepared by spin-coating usingdichlorobenzene as solvent, and the effects of different acceptor materials, massratio and heat treatment on the composite film were studied. The results showthat after adding SPFRGO, with the extension of the reduction time of GO andthe increase of SPFRGO content, the roughness of composite film became larger,which is due to decreased activity of reduced graphene oxide. The lightabsorption of composite film was enhanced and the intensity of PL spectradecreased. Among three composite films, P3HT:5-SPFRGO composite film hasthe best performance. As the content of5-SPFRGO increased, the absorptionintensity showed a decreasing trend after the first enhancement, the PL spectralintensity showed an increasing trend after the first reduction. When the contentof5-SPFRGO was10%, P3HT:5-SPFRGO composite film had the optimalperformance.