# Structural Engineering in Sn-Doped WO3 Multi-Phase Systems for Enhanced Transparent Heat Insulation

## TL;DR

This study improves transparent heat insulation by doping WO3 with Sn, enhancing near-infrared blocking while keeping visible light clear.

## Contribution

The study introduces a structural transformation in Sn-doped WO3 that boosts thermal insulation performance through multiphase formation.

## Key findings

- Sn-doped WO3 with a 0.9:1 Sn:W ratio achieved 93.9% near-infrared shielding efficiency.
- The transparent thermal insulation index (THI) of the best sample was 4.38, a 317% improvement over pure WO3.
- Phase separation in Sn-doped WO3 enhances oxygen vacancies and W6+ to W5+ reduction, improving NIR absorption.

## Abstract

Building energy conservation through the development of transparent thermal insulation materials that selectively block near-infrared radiation while maintaining visible light transmittance has emerged as a key strategy for global carbon neutrality. WO3 is a semiconductor oxide with near-infrared absorption capabilities. However, the limited absorption efficiency and narrow spectral coverage of pure WO3 significantly diminish its overall transparent thermal insulation performance, thereby restricting its practical application in energy-saving glass. Therefore, this study successfully prepared Sn-doped WO3 materials using a one-step hydrothermal method, controlling the Sn:W molar ratio from 0.1:1 to 2.0:1. Through evaluation of transparent thermal insulation performance of a series of Sn-doped WO3 samples, we found that Sn:W = 0.9:1 exhibited the most excellent performance, with NIR shielding efficiency reaching 93.9%, which was 1.84 times higher than pure WO3. Moreover, this sample demonstrated a transparent thermal insulation index (THI) of 4.38, representing increases of 184% and 317%, respectively, compared to pure WO3. These enhancements highlight the strong NIR absorption capability achieved by Sn-doped WO3 through structural regulation. When Sn doping reaches a certain concentration, it triggers a structural transformation of WO3 from monoclinic to tetragonal phase. After reaching the critical solubility threshold, phase separation occurs, forming a multiphase structure composed of a Sn-doped WO3 matrix and secondary SnO2 and WSn0.33O3 phases, which synergistically enhance oxygen vacancy formation and W6+ to W5+ reduction, achieving excellent NIR absorption through small polaron hopping and localized surface plasmon resonance effects. This study provides important insights for developing high-performance transparent thermal insulation materials for energy-efficient buildings.