Hefei Research Institute made a series of progress in the research of transparent conductive oxide films

Recently, the Research Institute of Functional Materials of the Institute of Solid State Physics, Chinese Academy of Sciences, Hefei Institute of Materials Science has made series of advances in the research of transparent conducting oxide (TCO) thin films. The related achievements have been successively in Advanced Electronic Materials (Adv. Electron. Mater.). 4, 1700476 (2018)), Journal of Materials Chemistry C (J. Mater. Chem. C 5, 1885 (2017)), Chemical Communications (Chem. Commun. 50, 9697 (2014)) and others.

In general, the transparency and conductivity of materials are incompatible with each other. Transparent substances (such as glass) in nature are often not conductive, and conductive substances (such as metals) are often opaque. The main measure to realize the coexistence of transparency and conductivity is to select a wide bandgap semiconductor or insulator to ensure high transparency in the visible region, and then introduce carriers by element doping to achieve conductivity. According to this method, a very important material system, TCO, having high visible light region transparency and good conductivity coexistence can be realized. To date, TCO films have been widely used in flat panel displays, solar photovoltaic cells, touch screens, and light emitting diodes.

The TCO material is classified into n-type, ie, electron-conducting, and p-type, hole-conducting, according to the type of conductive carriers. In the case of n-type TCO, recent reports indicate that the wide-bandgap perovskite BaSnO3-based TCO exhibits high room-temperature carrier mobility and is therefore expected to replace the widely used tin-doped indium oxide (In2O3:Sn, ITO). Become the next generation TCO material. The solid-state researcher prepared a perovskite BaSnO3 thin film based on the solution method. After La element doping and film dislocation density control, the room-temperature carrier mobility comparable to the vacuum-processed BaSnO3 thin film was obtained (~23). Cm2/Vs), and the visible light transmittance exceeds 80%, and it is suggested that the oxygen vacancy is an important controlling factor for determining the carrier mobility of the system. The related results were published in Applied Physics Letters (Appl. Phys. Lett. 106, 101906 (2015)). Further, the researchers increased the carrier concentration of the thin film by doping the Sn site with Sb to achieve a significant increase in the electrical conductivity of the thin film. A BaSnO3 based thin-film solution growth mechanism and electrical and optical properties were established. The related results were published in ACS Applied Energy Materials (ACS Appl. Energy Mater. 1, 1585 (2018)).

Compared with n-type TCO, the performance and application of p-type materials lag behind that of n-type materials. This is due to the electronic structure and band structure of metal oxides: metal atoms and oxygen atoms in metal oxides are ionically bonded, and the 2p energy level of oxygen is much lower than the valence band electron energy level of metals. Oxygen ions have strong electronegativity and have a strong localized confinement effect on valence-caused holes. Even if holes are introduced at the top of the valence band, they will form deep acceptor levels, leading to hole loading. The flutes are difficult to move through the material. Theoretical design has shown that transparent and p-type conductive coexistence can be obtained in the copper-iron ore system. The Ag-based Cu-based copper iron ore has a wider optical band gap and a lower light absorption coefficient. However, due to the easy decomposition of Ag2O, Ag-based copper-iron ore cannot be successfully prepared in an open system. The solid-state researchers successfully prepared Ag-based p-type copper iron ore AgCrO2 thin films for the first time in an open system based on the solution method. The film exhibits the self-assembled growth characteristics of the (001) crystal plane, and exhibits high room temperature conductivity and visible light transmittance. The related results were published in the Journal of Materials Chemistry C (J. Mater. Chem. C 5, 1885 (2017)) and were selected as the cover and 2017 hot article.

In addition, the researchers can effectively adjust the energy band structure and electronic structure of the material based on the electron-electron correlation effect, and design and prepare two new p-type TCO films. Strongly related Bi2Sr2Co2Oy thin films were prepared by the solution method. The films exhibited excellent p-type transparent and conductive characteristics. The room temperature conductivity exceeded 222 S/cm, and the visible light transmittance exceeded 50%. The results were published in Chemical Communications (Chem. Commun. 50, 9697 (2014)). A novel p-type transparent conductive oxide thin film material, perovskite La2/3Sr1/3VO3, was prepared by pulsed laser deposition. A good balance of conductivity and optical transmittance is achieved in this thin film material, and the highest value of transparent conductive has been obtained to date. Relevant results were published in Advanced Electronic Materials (Adv. Electron. Mater. 4, 1700476 (2018)) and were selected as roll inserts.

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