Photocoloration efficiency and stability of photoelectrochromic devices

Abstract

In this study, a novel performance indicator termed “photocoloration efficiency (PhCE)” has been used to characterize photoelectrochromic devices with different architectures, developed by our research group and by others. It was found that PhCE is a suitable index for photoelectrochromics that gives emphasis on coloration kinetics. With use of PhCE, the parameters affecting device performance were identified: for efficient operation, the dye-sensitized solar cell of the device must produce an open circuit voltage of at least 450mV at 1000W/m2 of illumination. For devices with solar cells above this threshold, it is the thickness of the electrochromic film that dictates the ultimate performance: at exposure energy densities up to 0.6Wmincm−2 different devices have different responses. At larger exposures however, PhCE values converge, and become proportional to the electrochromic film thickness. As for the device color, it can be tailored by alteration of the electrolyte thickness.The stability of a “partly covered” photoelectrochromic device has been tested experimentally. It was found that the device degraded after 70days of testing, due to desorption of the N3 dye from TiO2 into the electrolyte.