Characteristics of water-soluble polythiophene: TiO2 composite and its application in photovoltaics

Abstract

We have studied the characteristics of composites of an environmentally friendly water-soluble polythiophene sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate] (PTEBS) and $\mathrm{Ti}{\mathrm{O}}_2$ . We observed that the ultraviolet-visible absorption spectrum of low molecular weight PTEBS is redshifted possibly due to the formation of aggregates. Cyclic voltammetry reveals the values of highest occupied molecular orbitals and lowest unoccupied molecular orbitals for PTEBS. A factor of 7 in photoluminescence quenching indicates that the exciton dissociation and charge separation occur successfully at the $\mathrm{PTEBS}:\mathrm{Ti}{\mathrm{O}}_2$ (1:1 by weight) interface. This enhances the possibility that the separated charges will reach the electrodes before recombining. Scanning electron micrograph images show how the PTEBS and $\mathrm{Ti}{\mathrm{O}}_2$ are interconnected and form paths to the electrodes to improve charge transport. Photovoltaic devices with $\mathrm{Ti}{\mathrm{O}}_2:\mathrm{PTEBS}$ composite achieved an energy conversion efficiency of $\eta =0.015\%$ , a short circuit current of $J_{\mathrm{SC}}=0.22\mathrm{mA}∕{\mathrm{cm}}^2$ , an open circuit voltage of $V_{\mathrm{OC}}=0.72\mathrm{V}$ , and a fill factor of $\mathrm{FF}=0.29$ under $\sim 300\mathrm{mW}∕{\mathrm{cm}}^2$ white light illumination.