A Study on the Effect of Doping Silver Nanowires on the Spectral Properties of Cesium Tungsten Bronze Thin Films
Abstract
The study investigates AgNWs-doped Cs0.32WO3 films as a year-round energy-saving solution in comparison with ordinary glass and Cs0.32WO3 films. The article indicates that although Cs0.32WO3 provides superior solar radiation blocking compared to traditional materials, its performance is not up to par throughout the year due to high photothermal conversion and emissivity. Doping the films with AgNWs, with their low emissivity and high mid-far infrared reflectance, addresses this limitation. Approximately 98% of solar radiation falls within the range of 200 nm ~ 2500 nm band, in which the near-infrared (NIR) light in the band of 780 nm ~ 2500 nm constitutes 51% of this spectrum, while 96% of the thermal radiation of normal objects is concentrated within the mid-far infrared (MIR) band of 2.5 μm ~ 25 μm. Ordinary glass, with a thickness of 3 mm, exhibits a remarkable transmittance of 90% within the solar radiation spectrum, which will increase the energy consumption of cooling in summer months, while the absorbance in the mid-far infrared band reaches up to 88.1%, which will increase the heating energy consumption during winter. Based on the characteristics of intrinsic absorption, local surface plasmon resonance (LSPR), and small polaron absorption, cesium tungsten bronze (CsxWO3) exhibits a superior capacity to block solar radiation than tin oxide and other tungsten bronze materials. However, CsxWO3 film has an obvious photothermal conversion efficiency and a high emissivity, which will cause a strong radiation heat exchange with the indoor environment in summer and winter. Silver nanowires (AgNWs) have low emissivity and high mid-far infrared reflectance owing to their dense network structure, effectively mitigating the radiation heat exchange. In this paper, solid-state reaction method, ball milling, and centrifugation were used to prepare nano Cs0.32WO3 slurries (particle size is < 50 nm), then at T550nm = 70% and T550nm = 60%, eight samples of non-doped Cs0.32WO3 films, Cs0.32WO3 films doped with AgNWs, Low-E films, and double-sided coating films were prepared respectively to carry out the performance testing experiments. By simulating indoor heating in winter and indoor warming in summer, the experiments demonstrate that at a certain T550nm, for example, T550nm = 60%, the Cs0.32WO3 thin film doped with AgNWs can possess robust solar radiation blocking ability (B1400nm > 94%), low emissivity (εsurf < 0.35) and high mid-far infrared reflectance (RMIR > 65%), achieve a good energy saving effect both in winter and summer, effectively make up for the shortcoming of the non-doped Cs0.32WO3 films which show an inferior energy-saving performance during winter, and provide meaningful technical reference and data support for further optimization of Cs0.32WO3 thin film properties.