In this study, we investigated inverted hybrid bulk-heterojunction solar cells with the following configuration: fluorine-doped tin oxide (FTO) jTiO 2 ∕RGOjP3HT∶PC 61 BMjV 2 O 5 or PEDOT:PSS|Ag. The TiO 2 ∕GO dispersions were prepared by sol-gel method, employing titanium isopropoxide and graphene oxide (GO) as starting materials. The GO concentration was varied from 0.1 to 4.0 wt%. The corresponding dispersions were spin-coated onto FTO substrates and a thermal treatment was performed to remove organic materials and to reduce GO to reduced graphene oxide (RGO). The TiO 2 ∕RGO films were characterized by x-ray diffraction, Raman spectroscopy, and microscopy techniques. Atomic force microscopy (AFM) images showed that the addition of RGO significantly changes the morphology of the TiO 2 films, with loss of uniformity and increase in surface roughness. Independent of the use of V 2 O 5 or PEDOT: PSS films as the hole transport layer, the incorporation of 2.0 wt% of RGO into TiO 2 films was the optimal concentration for the best organic photovoltaic performance. The solar cells based on TiO 2 ∕RGO (2.0 wt%) electrode exhibited a ∼22.3% and ∼28.9% short circuit current density (J sc) and a power conversion efficiency enhancement, respectively, if compared with the devices based on pure TiO 2 films. Kelvin probe force microscopy images suggest that the incorporation of RGO into TiO 2 films can promote the appearance of regions with different charge dissipation capacities.
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