Semiconductor Materials - 09

Abstract

Earth is warming up! Buildings consume 30-40% of their electricity in air conditioning. Window coatings that promote near-infrared (NIR) shielding are essential. Harmful UV-A (315-400 nm) radiation reaching Earth’s surface is deemed a carcinogen, eliminating which is key to human health. Transparent conductive oxides like indium tin oxide (ITO) and cesium tungsten oxide (CWO) act as wavelength-selective absorbers in the NIR while providing high visible light transparency. But they exhibit reduced efficiency in UV-A (315-400 nm) absorption. Metal-free carbon dots (CDs) act as high-performance UV-A absorbers. Herein, we develop a new hybrid material composed of CWO nanoparticles and CDs, termed CWO-CDs, for high-performance NIR shielding and UV-A blocking (Figure 1 (a)). CDs provide very high UV-A absorption while assisting CWO nanoparticle aggregation, forming larger particle clusters. This change in size affects the plasma frequency response, leading to enhanced NIR absorption observed in Figure 1(b). Furthermore, porosity was increased by increasing the film thickness. Increased absorption in the NIR was attributed to internal scattering amongst the particle clusters. CWO-CDs film achieved solar blocking efficiency of 86% in the UV-A and 91.2% in the NIR. We demonstrated the heat shielding effect by an architectural miniature house model. Temperature vs time (Figure 1 (c)), shows temperature lowering as large as 12˚C, rendering it a safe indoor environment with reduced energy costs. Metal oxide semiconductors and carbon dots thus provide highly efficient solar heat and UV blocking, ideal for energy-saving window and skylight coatings.