Research progress on tungsten oxide materials in photovoltaic applications

Tungsten is China's dominant mineral resources, but China's tungsten resources and tungsten resources are seriously mismatched. Tungsten oxide is an important intermediate product of the tungsten industrial chain, but it is currently only used as a precursor material for tungsten powder. However, in fact, tungsten oxide materials have unique pore and defect structures, which have many unparalleled properties in many aspects and are widely used in many optoelectronic fields such as photo/electrochromism, photo/electrocatalysis, and trace detection. Application prospects.

Recently, Zhao Zhigang (Corresponding author), a researcher at the Suzhou Institute of Nanotechnology and Nanobionics of the Chinese Academy of Sciences, published an article titled Tungsten Oxide Materials for Optoelectronic Applications in the international journal Advanced Materials. From the complexity of phase structure and stoichiometric composition of tungsten-based oxide materials, this article briefly reviews the special photoelectric properties of other materials. In addition, the article focused on the research results of Zhao Zhigang's research team in recent years, described the latest research progress in the application of tungsten-based oxide materials in photovoltaic applications, and introduced the method of material design through targeted control of structure and composition. The strategy for improving the performance of tungsten-based oxides in many conventional applications is discussed. At the end of the article, the bright prospects and research trends of this versatile material, tungsten oxide, are anticipated.

The early work of the research team focused on the field of photocatalysis and aimed to improve the separation efficiency of photogenerated carriers in tungsten oxide materials. In 2008, the surface-mounted WO3 nanotube structure with Pt (Angew. Chem. Int. Ed. 2008, 47, 7051) was designed to perform well in the visible light catalytic degradation of gaseous acetaldehyde. WO3 octahedron obtained in 2010 (Chem. Comm. 2010, 46, 3321) and the "3 in 1" water treatment material H2W1.5O5.5·H2O (Chem. Commun. 2013, 49, 5787) developed in 2013, It is through surface acidification that the tungsten oxide material's ability to treat pollutants such as water, heavy metals or dyes is significantly increased.

Photochromism is another important property of tungsten oxide materials, which can be described as homologous to photocatalysis. For example, in the case where photo-generated carriers are trapped, the film-like tungsten oxide can be changed from transparent to blue, ie, a photochromic phenomenon occurs. In order to solve the limitations of tungsten oxide as a photochromic material, such as slow response, poor reversibility, and response to only ultraviolet light, Zhao Zhigang and his collaborators succeeded in the photochromism response of tungsten oxide in 2009 through the construction of an organic-inorganic hybrid system. The range extends to the near-infrared region (>700 nm) (Chem. Commun. 2009, 16, 2204). The following year, the photochromic response rate of the tungsten oxide material is greatly improved by loading the CdS quantum dots on the WO3 film. Adv. Funct. Mater. 2010, 20, 4162).

In the electrochromic field, the team promoted the development of smart color-changing technology from the aspects of host materials, electrolytes, and device structures, and achieved a series of progress in theory and application. In terms of material preparation, tungsten oxide quantum dot materials were obtained for the first time, and it was confirmed that their excellent electrochromic properties come from the zero-dimensional particle-efficient material and charge transport process (Adv. Mater. 2014, 26, 4260). In terms of electrolyte development, we pointed out that traditional H+, Li+, and Na+ ions are used in the electrochromic field. For the first time, trivalent Al3+ was used as an intercalating ion to greatly increase the response rate, color efficiency, and cycling performance of the device (Adv. Funct. Mater). 2015, 25, 5833). In the aspect of device structure design, the integration of electrochromic technology with other emerging technologies was emphasized, and flexible graded electrochromic thin films (Chem. Commun. 2012, 48, 8252) and smart supercapacitors (Nano. Lett. 2014, 14, 2150) were obtained. New concepts and multi-function devices such as Angew. Chem. Int. Ed. 2016, 55, 7161).

The research team is also committed to promoting the use of tungsten oxide materials in more completely new areas. In 2015, the team used the oxygen-enriched W18O49 sea urchin-like nanoparticle as a surface plasmon resonance enhanced (SERS) substrate to obtain excellent SERS performance with high sensitivity and high detection limit. The detection limit can be as low as 10–7 M, and the enhancement factor can be improved. 3.4×105 is one of the most excellent semiconductor SERS substrates reported recently and is close to precious metal materials that have no “hot spot” effect. This work confirms that proper modulation of oxygen deficiencies in semiconductor oxides can be used as an effective means of significantly improving its SERS performance, breaking the limitations of precious metal substrates in conventional SERS techniques, and further broadening the use of semiconductor oxides as substrate materials in SERS. The scope of application in testing (Nat. Commun. 2015, 6, 7800).