Pressure Engineering Promising Transparent Oxides – Dr. Wenge Yang

Transparent conductive oxides ((TCO) display both high conductivity and optical transparency. This unique combination makes them the most commonly used transparent electrode materials, which are widely used in solar cells, touch screens, light-emitting diodes and etc. However, the traditional doping technology couldn’t further improve the conductivity and transparency of TCOs, thus limiting their further applications. Therefore, improving the conductivity and transparency of transparent conductive oxides is a key challenge in the research and design of transparent conductive materials.  New research from a team of scientists co-led by Dr. Wenge Yang from HPSTAR obtained a highly transparent and metastable phase with two orders of magnitude enhancement in conductivity in Ti-doped In₂O₃ by pressure treatment and thus proposed to apply pressure to modulate the lattice and electronic and optical properties precisely on TCOs. The study is published in Advanced Science.

Compared with chemical doping, pressure is a unique and more direct way without introducing chemical impurities into the sample, which can directly alter the distance between atoms and interatomic interactions, thus altering the crystal and electron band structure, and ultimately altering the properties of materials. In recent years, pressure has been proved to be an effective way to precisely tune the properties of functional materials. However, novel structures and favorable properties obtained under pressure often could not be remained to ambient condition. Therefore, if pressure is used as a means of regulation, the key is to ensure that the high-pressure state can be recovered to the ambient condition.

By using multiple high pressure in-situ measurements combined with theoretical calculations, the team systematically studied the evolutions of crystal structure, electrical conductivity and optical properties of Ti-doped In₂O₃ (a classic TCO material) under high pressure. They found that titanium-doped indium oxide underwent an irreversible crystal structure transformation under pressure－after pressure release, the high-pressure structure was well preserved. Compared with the original sample, the electrical conductivity of the recovered sample was increased by about 100 times and shew a higher thermal stability, while still kept the optical transparency with better blocking efficiency of hazardous blue light (400-460 nm). In addition, their further theoretical simulations also support the correlation between the structure-properties and pressure treatment of TCO. Their study show that pressure provides an effective way to optimize the structure and properties of transparent oxides, enabling transparent oxides to have a wider field of applications.

Caption: Sample preparation, characterization, and performance for as-prepared (AP) and high-pressure released (RP) indium titanium oxide (ITiO) samples.Our results show that significant progress in optimizing the electrical and optical properties of TCO via pressure engineering.

透明导电氧化物同时显示高导电性和光学透明度，这种奇特的组合使其作为最常用的透明电极材料，被广泛地用于太阳能电池、平板显示器、触摸屏和发光等二极管。然而，传统的掺杂制备工艺无法进一步同时提升透明导电氧化物的导电性和透明度，从而限制了透明氧化物的进一步应用。因此，提高透明导电氧化物的导电性和透明度是透明导电材料研究与设计的关键挑战。近日，东北大学王沿东研究团队与北京高压科学研究中心杨文革、刘罡研究团队合作，从材料的晶体结构多态性角度出发，在透明导电氧化物钛掺杂氧化铟中，首次在高压下实现了透明氧化物的电导率和光学性能的同步优化。相关结果以“Pressure Engineering Promising Transparent Oxides with Large Conductivity Enhancement and Strong Thermal Stability“为题发表于Advanced Science。