Novel tunneled phosphorus-doped WO3 films achieved using ignited red phosphorus for stable and fast switching electrochromic performances†
Simultaneous improvement of both the performance and stability of electrochromic devices (ECDs) to encourage their practical use in various applications, such as commercialized smart windows, electronic displays, and adjustable mirrors, by tuning the film structure and the electronic structure of transition metal oxides remains a challenging issue. In the present study, we developed novel tunneled phosphorus (P)-doped WO3 films via the ignition reaction of red P. The ignited red P, which can generate exothermic energy, was used as an attractive factor to create a tunneled structure and P-doping on the WO3 films. Therefore, by optimizing the effect of ignited red P on the WO3 films, tunneled P-doped WO3 films fabricated by using 1 wt% red P demonstrated a striking improvement of the EC performances, including both a fast switching speed (6.1 s for the colouration speed and 2.5 s for the bleaching speed) caused by the improvement of Li ion diffusion by the tunneled structure and electrical conductivity by P-doping WO3 and a superb colouration efficiency (CE, 55.9 cm2 C−1) as a result of increased electrochemical activity by the elaborate formation of the tunneled structure. Simultaneously, this film displayed a noticeable long-cycling stability due to a higher retention (91.5%) of transmittance modulation after 1000 electrochromic (EC) cycles as compared to bare WO3 films, which can mainly be attributed to the optimizing effect of the tunneled structure to generate an efficient charge transfer and an alleviated structural variation during the insertion–extraction of Li ions. Therefore, our results suggest a valuable and well-designed strategy to manufacture stable fast-switching EC materials that are fit for various practical applications of the ECDs.