Interplay of Temperature-Induced Modification in Niobium Oxide Thin Films for Electrochromic Advancements

Niobium oxide (Nb₂O₅) is a compelling preference for electrochromic (EC) applications due to its remarkable optical modulation, chemical resilience, and efficient charge accommodation. This study attentively explores the influence of reaction temperature on the structural, morphological, and EC characteristics of Nb₂O₅ thin films synthesized via a hydrothermal approach. Reaction temperatures spanning 140 °C to 200 °C were optimized to unravel their pivotal role in dictating material properties and device performance. Field-emission scanning electron microscopy elucidates significant morphological transformations, transitioning from agglomerated, cracked structures at lower temperatures to well-defined, porous architectures at optimal conditions, followed by a re-compaction of the surface at elevated temperatures. Electrochemical analysis established a strong correlation between thermal-induced structural refinements and enhanced EC performance metrics. The optimized N-180 thin films exhibit enhanced charge injection dynamics, improved coloration efficiency of 81.33 cm²/C, and superior optical modulation of 74.13% at 600 nm. The device fabricated with the most favorable film demonstrated significant optical contrast and long-term stability, reinforcing its practical viability for smart window and energy-efficient applications. This study pioneers a comprehensive understanding of the thermal modulation of Nb₂O₅ thin films, providing new insights into the interplay between reaction temperature and material functionality.