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.

Broad-Spectrum Ultrathin-Metal-Based Oxide/Metal/Oxide Transparent Conductive Films for Optoelectronic Devices

“…From the refractive index n i and the extinction coefficient k i of the layer, the perpendicular components of the wave vector β i = ( k i 2 – q 2 ) 1/2 and the parallel components of the wave vector can be deduced. For the specific calculation process, refer to our previous research Figure b presents the simulated transmittance over the wavelength range of 400–1200 nm on the basis of the transfer matrix method, where the thickness of the Ag–Zn­(O) film is fixed at 5 nm.…”

“…For the specific calculation process, refer to our previous research. 53 Figure 4b presents the simulated transmittance over the wavelength range of 400−1200 nm on the basis of the transfer matrix method, where the thickness of the Ag−Zn(O) film is fixed at 5 nm. The simulated results show that the OMO compound films have higher transmittance when the top and bottom MGZO thicknesses are between 40 and 70 nm.…”

A Review on the Materials Science and Device Physics of Semitransparent Organic Photovoltaics

“…In multi-layer oxide/metal/oxide electrodes, such as ZnO/Ag/IZO, GZO/Ag/GZO, ITO/Au/ITO, and MoO 3 /Ag/MoO 3 , the oxide layers increase the transmittance due to lower reflection at both metal interfaces and offer low resistance [76]. Grown via lowtemperature reactive plasma deposition (RPD), the damaging effects can be minimized, as proposed by Zhang et al, that come with other oxide deposition methods, such as thermal evaporation, atomic layer deposition (ALD), and magnetron sputtering [76].…”

Analysis of the Effect of Graphene, Metal, and Metal Oxide Transparent Electrodes on the Performance of Organic Optoelectronic Devices

“…For instance, finite-difference time-domain (FDTD), transport matrix method, etc. [ 37 ]. Lee and coworkers measured the film thickness, refractive index, and extinction coefficient of the OMO electrode and performed optical simulations with Essential Macleod, and changed the thickness of the bottom and top oxide layers to increase the transmittance while keeping the R s constant, and similar to the experimentally measured data, the optimized SiInZnO (SIZO)/Ag/SIZO TE has 96.67% transmittance at 550 nm and R s is 6.41 Ω/sq [ 118 ].…”

“…Therefore, the metal film is usually prepared with metal oxide to form an OMO structure [ 36 ]. OMO structure combines the high electrical conductivity of metal film with the superior optical transmittance of metal oxide, the property of its structure has also made it widely investigated [ 37 ].…”