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 a series of advances in transparent conductive 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 transparent properties 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 achieve the coexistence of transparency and conductivity is to choose Wide bandgap semiconductors or insulators are used to ensure high transparency in the visible light region, and carriers are introduced by element doping to achieve conductivity. According to this method, a class with high visible light region transparency and good conductivity coexistence can be realized. The important material system is TCO. To date, TCO films have been widely used in flat panel displays, solar photovoltaic cells, touch screens, and light emitting diodes.
TCO materials are classified into n-type, ie, electron-conducting type, and p-type, hole-conducting type, based on the type of conductive carriers. In terms of n-type TCO, recent reports indicate that the wide bandgap perovskite BaSnO3-based TCO exhibits high levels. The room-temperature carrier mobility is expected to replace the widely used tin-doped indium oxide (In2O3: Sn, ITO) as the next-generation TCO material. The solid-state researchers prepared a perovskite BaSnO3 film based on the solution method. Elemental doping and film dislocation density control resulted in room-temperature carrier mobility (~23 cm2/Vs) comparable to that of a vacuum-produced BaSnO3 film, and visible light transmittance exceeding 80%, and oxygen vacancy was proposed. It is an important regulatory factor that determines the mobility of carriers in this system. Related results were published in Applied Physics Letters (Appl. Phys. Lett. 106, 101906 (2015)). Further, researchers increased the thin film by doping with Sb at the Sn site. The carrier concentration has greatly improved the conductivity of the thin film, and the BaSnO3 based thin film solution method has been established to correlate the growth mechanism with the optoelectronic properties. 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 material systems. This is due to the electronic structure and band structure of metal oxides: Metal atoms and oxygen atoms in metal oxides are ionically bonded. The 2p energy level of oxygen is much lower than the valence band electron energy of metal. Because oxygen ions have strong electronegativity, the vacancies with the top of the valence band have a strong localized binding effect, so that even at the valence band top The introduction of vacancies will also form deep acceptor levels, leading to hole carriers that are difficult to move in the material. Theoretical design has shown that transparent and p-type conductivity can be obtained in the delafossite system. Ag- and Cu-based The copper-iron ore phase has a wider optical bandgap and lower light absorption coefficient. However, due to the easy decomposition of Ag2O, the Ag-based copper-copper iron ore cannot be successfully prepared in an open system. The researchers of the solid state are based on the solution method. For the first time, an Ag-based p-type copper-iron ore AgCrO2 thin film was successfully prepared in an open system. The thin film exhibited the (00l) crystal plane self-assembled growth characteristics and exhibited high room temperature conductivity and visible light transmittance. In Journal of Materials Chemistry C (J. Mater. Chem. C 5, 1885 (2017)), was 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. Two new p-type TCO films were designed and prepared. The strong-association Bi2Sr2Co2Oy thin film was prepared by a solution method and the film showed excellent performance. P-type transparent conductive features, room temperature conductivity exceeds 222 S/cm, visible light area transmittance exceeds 50%. Related results were published in Chemical Communications (Chem. Commun. 50, 9697 (2014)). Pulsed laser deposition was used to prepare a A new type of p-type transparent conductive oxide thin film material - perovskite structure La2/3Sr1/3VO3. In this thin film material to achieve a good balance of conductivity and optical transmittance, to obtain the highest value of transparent conductivity so far Related results were published in Advanced Electronic Materials (Adv. Electron. Mater. 4, 1700476 (2018)) and were selected as roll inserts.
