Effects of deposition of an ultra-thin Al2O3 layer via atomic layer deposition on electrochromic property, self-discharge, and discharge capacity of photo-electrochromic devices

Photo-electrochromic devices (PECDs) can be spontaneously colored by sunlight and used as energy storage devices. The major obstacle to improving the performance of PECDs is the self-discharge at the interface between electrolyte and electrochromic layers. To prevent self-discharge, we deposited ultra-thin Al2O3 films on the WO3 electrochromic layer using atomic layer deposition (ALD). The ALD-deposited Al2O3 layer effectively suppressed the self-discharge phenomenon that results from the reduction of iodine. Therefore, the transmittance modulation (Delta T), photocharged voltage, and discharge capacity increased with an increasing number of ALD cycles. Specifically, the discharge capacity of the PECD-A5 sample fabricated with five ALD cycles increased by 63.7% compared to the PECD without an Al2O3 layer. However, the relatively thick Al2O3 layer of the PECD-A10 sample fabricated with ten ALD cycles resulted in performance degradation due to the slow Li+ ion diffusion rate.