Electrical and Optical Characterization of Sputtered Silicon Dioxide, Indium Tin Oxide, and Silicon Dioxide/Indium Tin Oxide Antireflection Coating on Single-Junction GaAs Solar Cells

Wen-Jeng Ho,Jheng-Jie Liu,Wen-Bin Bai,Jian-Cheng Lin,Hung-Pin Shiao

doi:10.3390/ma10070700

Abstract

This study characterized the electrical and optical properties of single-junction GaAs solar cells coated with antireflective layers of silicon dioxide (SiO2), indium tin oxide (ITO), and a hybrid layer of SiO2/ITO applied using Radio frequency (RF) sputtering. The conductivity and transparency of the ITO film were characterized prior to application on GaAs cells. Reverse saturation-current and ideality factor were used to evaluate the passivation performance of the various coatings on GaAs solar cells. Optical reflectance and external quantum efficiency response were used to evaluate the antireflective performance of the coatings. Photovoltaic current-voltage measurements were used to confirm the efficiency enhancement obtained by the presence of the anti-reflective coatings. The conversion efficiency of the GaAs cells with an ITO antireflective coating (23.52%) exceeded that of cells with a SiO2 antireflective coating (21.92%). Due to lower series resistance and higher short-circuit current-density, the carrier collection of the GaAs cell with ITO coating exceeded that of the cell with a SiO2/ITO coating.

Highlights

Indium tin oxide (ITO) is among the most widely used transparent conducting oxides (TCOs) due to its high electrical conductivity and high optical transparency [1–4]
We examined the electrical and optical properties of the indium tin oxide (ITO) films as well as the dark current-voltage (I-V), optical reflectance, and external quantum efficiency of the resulting gallium arsenide (GaAs) solar cells
Fabrication of single-junction GaAs solar cells involved the deposition of a grid pattern n-ohmic contact (AuGe/Ni/Au) on the n+ -GaAs contact layer with an AuBe/Ti/Au p-ohmic contact deposited on the rear surface of p+ -type GaAs substrate via e-beam evaporation

Summary

Introduction

Indium tin oxide (ITO) is among the most widely used transparent conducting oxides (TCOs) due to its high electrical conductivity and high optical transparency [1–4]. TCO films can be deposited on surfaces using various techniques, such as DC-sputtering, RF-sputtering, electron-gun evaporation, chemical vapor deposition, and spray hydrolysis. Thin films of TCO are used as transparent electrodes in organic optoelectronic devices [5]. ITO can be applied to all types of solar cell, those based on thin films [6–9]. The electrical conductivity and optical transparency of ITO films can be improved when applied via sputtering at high temperatures in a growth environment that includes an appropriate quantity of oxygen [10–14]. The high electron mobility and direct bandgap of gallium arsenide (GaAs) has led to its use in high-speed RF electronics and optoelectronics [15,16]

Methods

Results

Conclusion