Abstract
Screening for potential new materials with experimental and theoretical methods has led to the discovery of many promising candidate materials for p-type transparent conducting oxides. It is difficult to reliably assess a good p-type transparent conducting oxide (TCO) from limited information available at an early experimental stage. In this paper we discuss the influence of sample thickness on simple transmission measurements and how the sample thickness can skew the commonly used figure of merit of TCOs and their estimated band gap. We discuss this using copper-deficient CuCrO as an example, as it was already shown to be a good p-type TCO grown at low temperatures. We outline a modified figure of merit reducing thickness-dependent errors, as well as how modern ab initio screening methods can be used to augment experimental methods to assess new materials for potential applications as p-type TCOs, p-channel transparent thin film transistors, and selective contacts in solar cells.
Highlights
There are a wide range of transparent conducting oxides (TCOs) available for today’s optoelectronic applications [1,2,3,4,5,6,7]
Extensive research is being undertaken to find new candidate materials in particular, to replace In-rich TCOs and to find viable hole conducting counterparts (p-type TCOs). The former is driven by increasing indium costs and the desire for high-mobility TCOs to minimise free carrier absorption for solar cell applications, while the latter is required for novel fully-transparent optoelectronics. p-type TCOs have been reported since 1997 starting with CuAlO2 by Kawazoe et al [8]
Sample synthesis: All p-type TCOs (Cu0.4 CrO2 ) directly measured for this study were synthesised by spray pyrolysis using solutions of 0.025 M chromium acetyl-acetonate and
Summary
There are a wide range of transparent conducting oxides (TCOs) available for today’s optoelectronic applications [1,2,3,4,5,6,7]. Extensive research is being undertaken to find new candidate materials in particular, to replace In-rich TCOs and to find viable hole conducting counterparts (p-type TCOs) The former is driven by increasing indium costs and the desire for high-mobility TCOs to minimise free carrier absorption for solar cell applications, while the latter is required for novel fully-transparent optoelectronics. Many other oxides showing p-type conductivity have been found, ranging from other oxides in the delafossite crystal structure family [8,9,10,11] to spinels [12,13,14], perovskites [15], and corundum-type oxides [16,17,18] While many of these p-type oxides have been used in laboratory demonstration devices, their performance in terms of transparency, conductivity, and hole mobility is still severely lacking, and experimental and computational screening for new and better-performing p-type TCOs continues. We will review its use in the literature and highlight potential shortcomings of this approach when the figure of merit is used incorrectly
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