Over 500°C stable transparent conductive oxide for optoelectronics

Abstract

High-temperature stable transparent conductive oxides (TCOs) are highly desirable in optoelectronics but are rarely achieved due to the defect generation that is inevitable during high-temperature air annealing. This work reports unprecedented stability in aluminum and fluorine co-doped ZnO (AFZO) films prepared by pulse laser deposition. The AFZO can retain a mobility of 60 cm² V⁻¹ s⁻¹, an electron concentration of 4.5 × 10²⁰ cm⁻³, and a visible transmittance of 91% after air-annealing at 600°C. Comprehensive defect characterization and first principles calculations have revealed that the offset of substitutional aluminum by zinc vacancy is responsible for the instability observed in aluminum-doped ZnO, and the pairing between fluorine substitution and zinc vacancy ensures the high-temperature stability of AFZO. The utility of AFZO in enabling the epitaxial growth of (Al_xGa_1−x)₂O₃ film within a high-temperature, oxygen-rich environment is demonstrated, facilitating the development of a self-powered solar-blind ultraviolet Schottky photodiode. Furthermore, the high-mobility AFZO transparent electrode enables perovskite solar cells to achieve improved power conversion efficiency by balancing the electron concentration-dependent conductivity and transmittance. These findings settle the long-standing controversy surrounding the instability in TCOs and open up exciting prospects for the advancement of optoelectronics.