PEDOT:PSS 변색층 기반 전기변색 소자의 성능 최적화

Abstract

This study systematically evaluated various electrolyte compositions and electrochromic layer designs to optimize the performance of electrochromic devices (ECDs) based on the conductive polymer Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). ECDs operate on the principle of reversible color changes induced by electrochemical reactions under external electrical stimuli, enabling their application in a wide range of fields such as smart windows, wearable displays, and energy-saving windows. To enhance the optical performance and response speed of ECDs, the thickness of the PEDOT:PSS electrochromic layer and the electrolyte composition were systematically optimized. By applying spin-coating speeds ranging from 400 to 900 rpm to adjust the layer thickness, a maximum transmittance change (▲T) of 54.45% was observed at 600 rpm, demonstrating superior electrochromic performance. In comparison, ▲T values of 48.32% and 46.78% were observed at 400 rpm and 900 rpm, respectively, confirming that 600 rpm provided the optimal conditions for layer thickness and performance. This result underscores the significant impact of electrochromic layer thickness on both optical performance and response time. Regarding the electrolyte composition, the PSS concentration was varied from 10% to 30%, with the 30% concentration showing the fastest color-switching times, including a coloring time (Tc) of 22 seconds and a bleaching time (Tb) of 2 seconds. However, concentrations above 30% led to decreased solubility, resulting in reduced electrolyte homogeneity. The introduction of ferrocenium (0.06 wt%) and L-ascorbic acid (0.035 wt%) into the electrolyte, while excluding tempo, yielded the fastest switching times with Tc of 3.5 seconds and Tb of 3 seconds, demonstrating the optimal composition. In repeated cycle testing, the device using the optimized electrolyte composition (a) maintained more than 70% of its initial performance after 100 cycles, demonstrating stable performance. In contrast, the device with the tempo-containing electrolyte (b) retained only 43.25% of its initial performance after 100 cycles, while the ferrocenium-only composition (c) maintained only 35.98% (▲T 18.66%). This confirms the superior long-term performance retention of the optimized electrolyte composition. Long-term stability tests further supported these findings. The device using the optimized electrolyte showed excellent performance retention with negligible degradation in transmittance after 10 cycles, even after 6 days. In contrast, the tempo-based electrolyte showed a more significant decline in performance, with transmittance differences exceeding 4% after 10 cycles. This indicates that the optimized electrolyte, which includes ferrocenium and L-ascorbic acid, outperforms the tempo-based electrolyte in maintaining long-term performance stability. Additionally, large-area ECDs were fabricated using slot-die coating to improve the uniformity of the electrochromic layer. A 10×10 cm large-area device was successfully manufactured using two types of PEDOT:PSS solutions, PTE1 and PH1000. These devices demonstrated stable performance in large-area applications, with PTE1 showing superior coating uniformity and PH1000 achieving faster response times. This result validates the feasibility of large-area ECDs for practical applications, including large-scale smart windows. In conclusion, this study presents optimized electrolyte compositions and electrochromic layer designs that significantly enhance the performance of PEDOT:PSS-based ECDs, thereby contributing to the development of high-efficiency electrochromic devices. The results also demonstrate the superior long-term stability of the optimized electrolyte composition, offering promising prospects for practical applications requiring reliable and durable electrochromic materials.