Accelerated screening of Cu–Ga–Fe oxide semiconductors by combinatorial spray deposition and high-throughput analysis

Abstract

The discovery of new materials with a well-defined set of properties is a work-intensive and time-consuming task, when relying on conventional experimental routines. The employment of high-throughput (HT) techniques speeds up the screening of material properties and facilitates the generation of material libraries for data-driven optimization. Ultrasonic spray pyrolysis (USP) is an up-scalable technique, well-suited for creating combinatorial thin films, enabling two-dimensional variation of the film composition and/or thickness which can be used in an HT approach. In this work, we upgraded a commercial USP tool with a custom-built, electronically controlled pump system that allows for a gradual composition change of the precursor solution during the deposition process. The capabilities of the realized equipment are demonstrated by depositing a 2D composition gradient of copper–gallium–iron oxides, with demonstrated process reliability and material stability under ambient conditions. This elemental system is relevant for applications in photovoltaic, photo-electrochemical or optoelectronic devices, where the materials can be used as transparent electrodes, charge carrier selective or absorber layers, depending on the obtained phases and composition. Spatially resolved elemental quantification of the 2D deposits is performed by HT-SEM/EDS, revealing a concentration distribution of the metal oxides with a stoichiometry range of Cu_14–49Ga_21–59Fe_14–44. Crystallographic information is gathered through HT-XRD point measurements which yield maps of identified structures, i.e., spinel, delafossite, CuO, and Cu₂O. The film thickness distribution in a range of 400–650 nm is obtained through Monte Carlo simulations of EDS measurements and verified using tactile profilometry. The optical properties of the thin films are determined by HT-FT transmission measurements, yielding maps of band gap energies ranging from 1.9 to 3.0 eV. The presented platform facilitates high-throughput screening of solution-based semiconductor films through combinatorial deposition and (semi-)automatized analysis, enabling a 10- to 100-fold speed-up with over 96% compositional reproducibility and over 98% reproducibility of the evaluated band gap energy.