Efficiency enhancement of solid-state dye-sensitized solar cells by doping polythiophene films photoelectrochemically grown onto TiO2 nanoparticles covered with cis-bis(isothiocyanato) bis(2,2′-bipyridyl-4,4′-dicarboxylato)ruthenium(II)

Abstract

We recently reported on the effect of dopant sizes on the performance of polythiophene (PT)-based solar cells wherein the PT film was polymerized with 3-{5-[N,N-bis(4-diphenylamino)phenyl]thieno[3,2-b]thiophen-2-yl}-2-cyano-acrylic acid (C207) pre-adsorbed onto the electrode. Herein we utilized n- and p-doped polythiophene (PT) films as part of the solid-state dye-sensitized solar cell (ssDSSCs) based on cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)ruthenium(II) (N3), the most commonly used dye sensitizer. Although the structure of the N3 is different from the chain-like C207, a smooth and homogeneous PT film can still be grown photoelectrochemically into the pores and onto the surface of the N3-covered TiO2 nanoparticles. The PT films were electrochemically doped with anions (ClO4− or PF6−) and cations (tetrabutylammonium, TBA+, or tetramethylammonium, TMA+). TMA+, being smaller, leads to a higher doping level in the PT films and a power conversion efficiency of 7.57 ± 0.33%, which is a 33% increase over that constructed with undoped PT films. However, the efficiency of the anion-doped PT films is reduced when compared to that of the undoped PT films. The N3-sensitized solar cell comprising a TMA+-doped PT film is 15% more efficient and costs at least 57% less than the PT-based solar cell comprising C207. This study demonstrates that the n-doped PT film can be a useful interfacial modifier, and pre-adsorbed N3 not only assists the growth of smooth PT films, but also enhances light absorption and power conversion efficiency of the resultant DSSC.