Low-Temperature Oxide/Metal/Oxide Multilayer Films as Highly Transparent Conductive Electrodes for Optoelectronic Devices

Abstract

Transparent conductors are essential for optoelectronic devices and flexible electronic devices. Oxide/metal/oxide (OMO) multilayer films with outstanding photoelectric performance have become a promising alternative for traditional transparent conductive oxides (TCOs). Most of the oxide films in OMO are deposited by magnetron sputtering or thermal evaporation processes, while the strong ion bombardment or high temperatures would deteriorate the device performance. For example, to fabricate a semitransparent solar cell, a top OMO will need to be deposited on the top of the semiconductor layer. Great care needs to be taken to reduce the damage to the semiconductor material to reduce the possible trapping of photogenerated charges. Recently, Mg and Ga codoped ZnO (MGZO) has been developed because of its wider spectral transmittance and less damage to the underlying functional layers in optoelectronics. However, the conductivity of MGZO remains limited. To produce low sheet resistance, the layer thickness needs to be several hundred nanometers. Here, we present high-quality MGZO films that are deposited by the reactive plasma deposition (RPD) technique with a soft growth process at room temperature (without intentional heating), providing broadband transmission and ultrathin pure Ag films prepared by magnetron sputtering at room temperature. Compared with the single MGZO, MGZO/Ag/MGZO multilayers effectively improve thin-film conductivity while maintaining high transmittances. The transfer matrix method (TMM) is used to determine the optimum thickness of each layer in OMO, and there is an excellent agreement between the simulation and experimental results. An MGZO/Ag/MGZO (40/9.5/45 nm) transparent electrode on a glass substrate presents an average transmittance of 87% (including glass) over a spectral range of 400–800 nm (relative transmittance, 94.7%), and sheet resistance (10 Ω sq–1). A semitransparent perovskite solar cell with an OMO top electrode exhibits a photoelectric conversion efficiency of about 11%. This work provides an insight to grow high-quality OMO films combining the RPD-TCO technique of high-rate deposition and low ion bombardment with ultrathin Ag films at room temperature, which pushes OMO forward to practical applications in more diverse optoelectronic devices.