Study of Band Gap Reduction of TiO2 Thin Films with Variation in GO Contents and Use of TiO2/Graphene Composite in Hybrid Solar Cell

Abstract

Organic photovoltaic devices are the main focus of research among the other OPV due to various advantages like low cost, versatility of materials used in terms of tunability of their electrical and optical properties, and ease of fabrication. However, the challenges of the tunability of band gap and stability are still the barrier towards the commercialization of OPV. The most widely used donor polymer in OPV devices is poly (3-hexylthiophene) (P3HT) due to excellent optical properties for efficient photovoltaic devices. The sol processed metal oxide nanostructure provides excellent carrier transport properties by their high mobility and good optical properties for P3HT based solar devices. The device was designed to improve the performance of the P3HT based photovoltaic devices using TiO2/Graphene composites. The condensed refluxed sol gel technique was used to synthesis the TiO2 nanoparticles having titanium isopropoxide as a precursor and Modified Hummer’s Method for the oxidation of graphite flakes into graphene oxide GO having KMnO4 as an oxidizing agent. TiO2/Graphene composite was prepared by the sonication of GO into TiO2 sol and then heated at 60oC for 20 hours. The thin films were fabricated using spin coating technique and then annealed at 500oC to achieve the anatase phase of TiO2 nanoparticles and reduced graphene oxide rGO. TiO2/Graphene films were characterized using SEM, showed the homogenous distribution of graphene nanosheets among the homogenously distributed titania nanoparticles of size range (15nm-22nm). XRD showed the pure anatase phase peaks of TiO2 nanoparticles and oxidation of graphite at 11.8o with interplanner distance of 7.5oA. UV-Vis spectroscopy showed the peaks of oxidation of the graphite at 216 nm and all the composite films were in visible region. The band gap was calculated both by Cyclic Voltammetery (CV) and UV-Vis Spectroscopy, reduced from 3eV to 2.71eV. The chemical bonding Ti-O-C resulted in enhances the electron transport in obtained composite films. Significant progress in the performance of IV characteristics of organic solar cells was achieved using the TiO2/Graphene composite as electron collector in active layer along with P3HT: PCBM in inverted organic photovoltaic devices.