Dye-sensitized solar cells containing reduced graphene oxide for enhancing performance

Abstract

Dye-sensitized solar cells containing reduced graphene oxide for enhancing performance was discussed and proved its profits Various graphene oxide (GO) samples were prepared using the Hummers method under different synthesis conditions The obtained GO samples were evaluated for the yields and characterized for the microstructure surface chemistry and optical transmittance The effects of the chemical concentrations and the addition rates of the chemical and water on the yields and characteristics are reported The GOs obtained consist of a few layers and exhibit good crystallinity It was found that the yield was mainly affect by the water dropping rate as well as the NaNO3/KMnO4 ratio Also the resulting GOs are quite similar regardless of the synthesis conditions except that the graphite clusters vary slightly in their sizes GO coatings exhibit optical transmittance greater than 80% has been obtained Furthermore the use of reduced GO (RGO) to bridge TiO2 particles in the photoanode of dye-sensitized solar cell (DSC) for reduced electrical resistance has been investigated The difficulty in dispersing RGO in TiO2 paste was overcome by first dispersing GO into the TiO2 paste The GO was then reduced to RGO after the sintering of TiO2 Depending on the amount of RGO in the photoanode the cell performance was enhanced to different degrees A maximum increase of 11 4 % in the cell efficiency has been obtained In particular the inclusion of graphene has reduced the electron diffusion time by as much as 23 4% i e from 4 74 to 3 63 ms and increased the electron lifetime by as much as 42 3% i e from 19 58 to 27 85 ms In order to fabricate true flexible DSC (FDSC) using Titanium (Ti) foil and indium tin oxide coated polyethylene naphthalate as the substrates for the photoanode and the counter electrode respectively Two types of TiO2 powders were used for making the photoanodes namely commercial TiO2 particles (P25) and homemade TiO2 mesoporous beads RGO was included in selected photoanodes to improve the electrical conductivity The fabricated cells have either a TiO2 compact layer (CL) or not The effects of CL RGO addition and the use of mesoporous TiO2 beads on the cell performance are presented and discussed We demonstrated that the optimized use of CL RGO and the beads improve the efficiency by as much as 154 % On the other hand the use of RGO connect between TiO2 particles in DSCs photoanaodes for reducing electrical resistance using heat treatment and ultraviolet(UV)-assisted reduction for GO has been investigated Before or after the calcination a UV-assisted reduction process was applied to remove the residuals in the photoanodes The photoelectrodes were then employed to make DSCs Depending on UV-assisted reduction treatment the cell performance was enhanced to various degrees A maximum increase of 8 24 % in the cell efficiency has been obtained Effects of graphene addition and the UV treatment on the characteristics of the photoanodes properties and the photovoltaic performances are discussed The resulting photoanodes were characterized using X-ray photoelectron spectroscopy (XRD) Raman microscopy scanning electron microscopy (SEM) X-Ray Photoemission Spectroscopy (XPS) transmission electron microscopy (TEM) and UV-vis-NIR optical spectroscopy Cell performance was evaluated using a solar simulator incident photon to electron conversion efficiency (IPCE) and electrochemical impedance spectroscopy (EIS) These shows DSCs containing RGO were applied for enhancing performance

Date of Award	2015 Dec 16
Original language	English
Supervisor	Jyh-Ming Ting (Supervisor)