Ga-Doped ZnO Coating—A Suitable Tool for Tuning the Electrode Properties in the Solar Cells with CdS/ZnS Core-Shell Quantum Dots

Mariya Aleksandrova,Jai Singh,Velichka Strijkova,Kostadinka Gesheva,Ajaya Kumar Singh,Tatyana Ivanova,Tsvetozar Tsanev

doi:10.3390/cryst11020137

Abstract

Two layer system from sputtered indium tin oxide (ITO) and gallium doped zinc oxide (Ga:ZnO, GZO) were studied for transparency in the visible electromagnetic range, reflectivity in the near infrared range, conductivity and valent band for a solar cells with quantum dots. The bi-layer coatings produced at optimized oxygen partial pressure, films thickness and surface roughness exhibit improved optical properties without worsening the electrical parameters, even if additional oxygen introduction during the reactive sputtering of the GZO. With an average optical transmittance of 91.3% in the visible range, average reflection and resistivity lower than 0.4 × 10−2 Ω.cm, these coatings are suitable for top electrode in the solar cells. The obtained results reveal that multilayered stacks of transparent ITO/Ga-doped ZnO coatings possess relatively low surface roughness (7–9 nm) and appropriate refractive index. The additional oxidation of GZO films induces modification of the film thickness and respectively of their optical performances.

Highlights

Transparent conductive films are an important part of any optoelectronic device.Especially in the solar cell fabrication, the efficiency of the cell is strongly dependent on the quality of the transparent conductive electrode (TCE) [1,2]
Sample Ga-doped ZnO (GZO) corresponds to non-additional oxidation, GZO1—to 10% additional oxidation, GZO2—to 20% additional oxidation; (c) refractive index of the indium tin oxide (ITO) film [26]
ITO/GZO by-layered coatings were deposited on glass substrates by RF sputtering at various oxygen contents

Summary

Introduction

In the solar cell fabrication, the efficiency of the cell is strongly dependent on the quality of the transparent conductive electrode (TCE) [1,2]. It usually consists of oxide film (transparent conductive oxide (TCO)) or a system of few TCOs involving few interfaces. This electrode serves as an electrical conductor, and as an optical filter. UV light causes materials degradation, shortening the solar cells’ life and the IR heating component affects the charge carriers’ mobility in the films, which results in a throughput decrease

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