Abstract
In this study, the impact of compositional variation in high resistance transparent (HRT) metal oxide ZTO films of thickness around 100nm has been investigated. The atomic composition in the films has been tailored by the change of RF power and sub-sequent thermal oxygenation in mixed nitrogen and oxygen atmosphere. A phase transition from ZnSnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> to ZnSnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> was observed in the X-ray diffraction spectra, indicating the possible oxygen incorporation into the films during the thermal annealing process. Uniform microstructures with compact interconnected grains of around 6-7 nm were found in SEM images while no significant changes been observed upon oxygenation. Besides, the significant alteration of electronic properties was noticed as an effect of compositional variation via oxygenation. All the films showed above 85% of optical transmittance in the visible light spectrum. The optimum optoelectronic properties for RF power has been determined as of 50W (ZnO) and 10W (SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) via thermal oxygenation at 400°C where the ratio O/(Zn+Sn) become around 1.6. The significant effect of oxygenation has been realized via primarily fabricated solar cells where the cell with ZnSnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> HRT shows higher efficiency than the ZnSnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> .
Highlights
In recent years, high resistivity transparent (HRT) metal oxide compounds have drawn widespread attention for improving the photovoltaic characteristics of thin-film heterostructure solar cells
We demonstrated extensively the impact of elemental composition on properties of Zin-Tin-Oxide (ZTO) thin films that have been tailored by radio frequency (RF) power in the co-sputtering technique and subsequent thermal oxygenation
The oxygenated films showed better crystallinity with a phase transformation from Zn2SnO3 to Zn2SnO4, there has no significant effect been observed in the mean crystallite size, dislocation density, and micro-strain for as-deposited and oxygenated films
Summary
High resistivity transparent (HRT) metal oxide compounds have drawn widespread attention for improving the photovoltaic characteristics of thin-film heterostructure solar cells. Using HRT materials as a buffer layer beneath of the cadmium sulfide (CdS) layers in cadmium telluride (CdTe), copper-indium-gallium-selenide (CIGS) and copperzinc-tin-sulfide (CZTS) thin-film solar cells can significantly ameliorate the pin-hole problem that is created due to the ultrathin CdS layer ((≤100 nm). The inclusion of an HRT layer shows improvement on the uniformity and junction quality in a manner parallel to that found for CdTe [5, 6], CuInSe2/CdS, and a-Si thin-film cells [7]. Among the aforementioned HRT materials, the ZTO shows very promising for solar cell application because of its high carrier mobility (in the range of 5–20 cm2/Vs) [13], high optical transmittance (above 80% in the visible region) and VOLUME XX, 2020
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