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 (ΔT), 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.