Blocking the Charge Recombination with Diiodide Radicals by TiO2 Compact Layer in Dye-Sensitized Solar Cells

Kazuteru Nonomura,Eva Unger,Anders Hagfeldt,Leif Häggman,Nick Vlachopoulos,Gerrit Boschloo

doi:10.1149/2.0281909jes

Abstract

The addition of a compact titanium dioxide (TiO2) layer between the fluorine-doped tin oxide (FTO) coated glass substrate and the mesoporous TiO2 layer in the dye-sensitized solar cell (DSC) based on the iodide/triiodide redox couple (I−/I3−) is known to improve its current-voltage characteristics. The compact layer decreases the recombination of electrons extracted through the FTO layer with I3− around the maximum power point. Furthermore, the short-circuit photocurrent was improved, which previously has been attributed to the improved light transmittance and/or better contact between TiO2 and FTO. Here, we demonstrate that the compact TiO2 layer has another beneficial effect: it blocks the reaction between charge carriers in the FTO and photogenerated diiodide radical species (I2−•). Using photomodulated voltammetry, it is demonstrated that the cathodic photocurrent found at bare FTO electrodes is blocked by the addition of a compact TiO2 layer, while the anodic photocurrent due to reaction with I2−• is maintained.

Highlights

During more than 30 years, intensive research and development has been carried out to improve the efficiency of dye-sensitized solar cell (DSC) and to enhance their environment-friendly natures; new materials have been proposed for the solar cell components, dyes,[3,4] electrolyte[5,6] and counter electrode,[7] and preparation methods and processes on different substrate such as plastic,[8] textile[9] laminated metal, and other have been elaborated.[10]
A thin compact metal oxide layer is deposited on the fluorine-doped tin oxide (FTO) substrate in dye-sensitized solar cells before deposition of the mesoporous TiO2 film.[12]
The compact layer can have a large effect on solar cell performance, especially when organic dyes are employed as sensitizer.[15]

Summary

Introduction

Dye-sensitized solar cells (DSCs) have been intensively investigated in last decades since Grätzel and co-workers made a breakthrough by employing a mesoporous structure for the semiconductor layer.[1,2] During more than 30 years, intensive research and development has been carried out to improve the efficiency of DSCs and to enhance their environment-friendly natures; new materials have been proposed for the solar cell components, dyes,[3,4] electrolyte[5,6] and counter electrode,[7] and preparation methods and processes on different substrate such as plastic,[8] textile[9] laminated metal, and other have been elaborated.[10]. A thin compact metal oxide layer is deposited on the FTO substrate in dye-sensitized solar cells before deposition of the mesoporous TiO2 film.[12]

Results

Conclusion