Chemically Bonded T/TT Nb ₂ O ₅ Heterojunctions with a Strong Internal Electric Field for High Performance Electrochromic Smart Windows

Transition metal oxides represent a prominent class of electrochromic materials for energy-saving smart windows. However, the reaction kinetics, essential for high electrochromic performance, has been hampered by inherently low electrical conductivity. Herein, we utilize a spontaneous phase transition strategy that introduces an internal electric field within a chemically bonded heterointerface to overcome this limitation. We demonstrate, both experimentally and theoretically, accelerated ion diffusion kinetics, with the Li+ diffusion energy barrier dramatically reduced from 0.48 to 0.19 eV, enabling large optical modulation (85.0%) and fast switching speed (7.3 and 5.3 s for coloring and bleaching, respectively). The resulting device demonstrates notable thermal management and energy-saving performance, achieving an impressive indoor temperature modulation of 13.1 °C and energy savings of up to 19%.