In situ image processing method to investigate performance and stability of dye solar cells

Abstract

A simple and non-destructive method is introduced using image processing to investigate changes in the performance of the dye solar cells (DSCs). The main principle is based on the fact that the most important DSC components (dye, electrolyte, catalyst) have a specific color which often changes as result of degradation. Here the imaging technique is demonstrated in the case of exposing DSCs on very harsh conditions (85 °C temperature and UV + Visible light). The aging of the cells was recorded with a color sensitive camera in a well regulated setup and the photographs were processed using image analysis techniques. A key factor in making the imaging method quantitative and suitable for aging studies is color calibration which is explained in detail. The image analysis of different cell configurations revealed that the bleaching reactions of the electrolyte were related to reactions between TiO2 and the electrolyte. The dye layer on the TiO2 was shown slow down the degradation. Furthermore the comparison of image analysis and current–voltage curves indicated that the performance degradation of the cells was only partly due to loss of tri-iodide. The loss of photocurrent and photovoltage was apparently largely due to the harmful effect of the by-products of the bleaching and/or the degradation of the dye. In addition, a small recovery effect due to the generation of tri-iodide under reverse bias condition was seen in both image analysis and electrical measurements.