Impedance Spectroscopic Investigation of the Degraded Dye-Sensitized Solar Cell due to Ageing

Parth Bhatt,Manoj Kumar,Kavita Pandey,Pankaj Yadav,Brijesh Tripathi

doi:10.1155/2016/8523150

Abstract

This paper investigates the effect of ageing on the performance of dye-sensitized solar cells (DSCs). The electrical characterization of fresh and degraded DSCs is done under AM1.5G spectrum and the current density-voltage (J-V) characteristics are analyzed. Short circuit current density (JSC) decreases significantly whereas a noticeable increase in open circuit voltage is observed. These results have been further investigated electroanalytically using electrochemical impedance spectroscopy (EIS). An increase in net resistance results in a lowerJSCfor the degraded DSC. This decrease in current is mainly due to degradation of TiO2-dye interface, which is observed from light and darkJ-Vcharacteristics and is further confirmed by EIS measurements. A reduction in the chemical capacitance of the degraded DSC is observed, which is responsible for the shifting of Fermi level with respect to conduction band edge that further results in an increase of open circuit voltage for the degraded DSC. It is also confirmed from EIS that the degradation leads to a better contact formation between the electrolyte and Pt electrode, which improves the fill factor of the DSC. But the recombination throughout the DSC is found to increase along with degradation. This study suggests that the DSC should be used under low illumination conditions and around room temperature for a longer life.

Highlights

The metal oxide based dye-sensitized solar cells (DSCs) have attracted significant attention of researchers in recent years, because of their economic fabrication process and efficient working under diffuse illumination
Different techniques have been used to analyze the degradation mechanisms in DSCs; Uam et al [10] used UVvis absorption spectroscopy to identify that the desorption of dye on the TiO2 surface was the reason for current density reduction in an aged cell
As received DSC shows a power conversion efficiency (η) of 4.0%, short circuit current density (JSC) of 9.92 mA/cm2, open circuit voltage (VOC) of 0.65 V, and fill factor (FF) of 60.9%, but after degradation η reduces to 3.6% with JSC of 7.74 mA/cm2, VOC of 0.685 V, and FF of 67%

Summary

Introduction

The metal oxide based dye-sensitized solar cells (DSCs) have attracted significant attention of researchers in recent years, because of their economic fabrication process and efficient working under diffuse illumination. The poor stability of DSC is mainly directed by the degradation mechanism occurring at different layers of the device after prolonged operation. Different techniques have been used to analyze the degradation mechanisms in DSCs; Uam et al [10] used UVvis absorption spectroscopy to identify that the desorption of dye on the TiO2 surface was the reason for current density reduction in an aged cell. Tatay et al [11] accompanied the UV-vis absorption spectroscopy with luminescence and cyclic voltammetry and observed that organic dyes formed molecular aggregates which could deteriorate the device efficiency. There are few studies which used electrochemical impedance spectroscopy (EIS)

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