Graphene quantum dots decorated electrospun TiO2 nanofibers as an effective photoanode for dye sensitized solar cells

Abstract

In this study, graphene quantum dots (GQDs) are prepared with an average size of ~15nm by a top down approach using carbon nanofibers (CNFs) to improve the photovoltaic performance of DSSCs. The titanium isopropoxide (Ti(OPr)4)/PVP precursor solution is used to get TiO2 NFs by electrospinning technique and then they are decorated with the prepared GQDs. First, the prepared GQDs are confirmed by XRD, Raman, TRPL, DLS, UV–vis, and PL Spectroscopy. The presence of GQDs onto TiO2 NFs is also confirmed by XRD, Raman spectroscopy and EDX studies. The surface morphology and the presence of GQDs onto TiO2 NFs are confirmed by SEM and TEM analysis. The optical properties of GQDs–TiO2 NFs are studied by UV–vis and PL spectroscopy. Finally, the dye sensitized solar cell is fabricated using GQDs decorated TiO2 nanofibers as the photoanode and standard Pt (Dyesol Ltd.) as the counter electrode and 0.5M 1-butyl-3-methylimidazolium iodide, 0.5M LiI, 0.05M I2, 0.5M 4-tertbutylpyridine, in acetonitrile as the electrolyte. A dye-sensitized solar cell (DSSC) with a photoanode based on GQDs–TiO2 NFs exhibited a high energy conversion efficiency of 6.22%, than the DSSC based on pure TiO2 NFs photoelectrode (4.81%), accompanied by an increment in both short-circuit photocurrent density and open-circuit voltage. The overall improvement in PCE is ~29.31% for GQDs decorated TiO2 NFs which is higher than other reported systems. The better photogenerated electron transfer ability, reduced charge recombination, increased dye adsorption, and an effective harvesting of visible light, which together added to an improvement in PCE. The stability test is performed for the DSSCs over a period of 30 days (720h) under one sun soaking, where GQDs decorated TiO2 NFs DSSCs is seen to retain ~99% of its initial normalized efficiency, thereby making it a viable option for practical applications.