Photovoltaic characteristics and stability of flexible dye-sensitized solar cells on ITO/PEN substrates

Improving the stability and understanding the degradation mechanisms of dye-sensitized solar cells (DSSCs) are essential for their commercialization and wide-spread use. Degradation mechanisms of DSSCs built on conductive glass substrates have been studied extensively, but very few studies have been carried out on cells built on flexible plastic substrates. Here we report the photovoltaic characteristics of flexible DSSCs, using TiO2 working electrodes on ITO/PEN films prepared by cold isostatic compression at different pressures, and their analysis using electrochemical impedance spectroscopy. The degradation mechanisms of the devices were investigated through long-term aging tests by exposing the DSSCs to indoor light at room temperature. Aging of these flexible DSSCs resulted in a widened potential difference between the conduction band potential of the TiO2 (E-c) and the Nernst potential of the redox couple (E-red), and reductions in recombination resistance and effective electron diffusion length due to gradual loss of particle contacts. In general, it was found that the compression technique can only improve the short-term photovoltaic performance of the devices. Their long-term stability does not depend on the compression pressure used and all the devices were gradually degraded due to reduced particle-particle contacts and particle-conductive layer contacts. These findings provide insights and directions towards the development of more stable, flexible DSSCs.