Enhanced Electrochromic Performance and Cycling Stability via Built‐In Electric Field in WO ₃ /Nb ₂ O ₅ Heterostructure

Abstract Tungsten trioxide (WO 3 ) is considered one of the most promising inorganic electrochromic materials due to its low cost, environmental friendliness, and high optical modulation capability. However, during the coloring/bleaching process, WO 3 films often suffer from performance degradation caused by ion trapping, resulting in slow response times and poor cycling stability. Herein, a transparent WO 3 /Nb 2 O 5 heterostructured electrode is designed, where a built‐in electric field is formed at the interface due to differences in band alignment and Fermi levels between WO 3 and Nb 2 O 5 . This internal field acts as a critical driving force for charge transfer and ion migration, thereby enabling a fast and reversible electrochromic response. The prepared WO 3 /Nb 2 O 5 heterostructure exhibits a high optical contrast (78.4% at 700 nm), fast switching speed (t c /t b = 9.3/10.4 s), and excellent cycling stability (maintaining 97.2% of its initial modulation after 10 000 cycles). Moreover, simulation results indicate that the electrochromic window based on the WO 3 /Nb 2 O 5 heterostructure demonstrate effective solar radiation regulation and significant energy‐saving potential across various global regions. This work provides an effective strategy for the rational design of electrochromic materials and holds great promise for applications in smart windows and intelligent display technologies.