Optical properties of CdS/CdTe heterojunction prepared by physical vapor deposition technique

L.` Nykyruy,Z Zapukhlyak,O Yaremiichuk,O Fedoryk,I Malyarska,R Yavorskyi,P Potera

doi:10.15330/pcss.19.3.209-216

Abstract

The paper presents the study of the optical properties of a thin layer of Cadmium Sulphide deposited on Cadmium Telluride films. CdTe thin films were obtained by vapor phase condensation method using different technological factors, in particular, different thickness (different time of deposition τ) on glass substrates. After deposition the optical properties were analysed by Swanepoel method, using transmission spectra. The upper thin layer of CdS was deposited by thermal evaporation method on CdTe thin films. The change in optical properties of CdS/CdTe heterojunction in comparison with CdTe thin films was investigated. Using a Swanepoel method were calculated the main optical constants, such as refractive index, absorption coefficient and optical conductivity. By this method the thickness of the thin film was determined and compared with the experimental values obtained by the profilometer.

Highlights

Thin film PV solar cell has been considered one of the promising solar cells due to its high energy conversion efficiency, low cost and convenience for large scale production
The real efficiency of PV solar cells based on the n-CdS / p-cadmium telluride (CdTe) heterojunction in a superstrate structure is currently 20.4 % [5], and the efficiency of solar modules with an area > 1 cm2 is 16.5 % [6, 7] The major impact factors for this difference are due to the optical losses, surface recombination, recombination in the space-charge region and rear contact effect
Absorption edge is about 800 nm for all samples, which is completely consistent with the width of the bandgap of CdTe thin films [26]

Summary

Introduction

Thin film PV solar cell has been considered one of the promising solar cells due to its high energy conversion efficiency, low cost and convenience for large scale production. The most successful thin film solar cells have been cadmium telluride (CdTe), copper indium gallium selenide (CIGS) and amorphous silicon (a-Si) with efficiencies of 18.3 %, 20 % and 12.3, respectively [1]. The efficiencies of thin-film solar cells are lower compared with silicon (wafer-based) solar cells, but manufacturing costs are lower. The theoretical efficiency of CdS/CdTe solar cells is predicted to be up to 28 – 30 % [3, 4]. The real efficiency of PV solar cells based on the n-CdS / p-CdTe heterojunction in a superstrate structure is currently 20.4 % [5], and the efficiency of solar modules with an area > 1 cm is 16.5 % [6, 7] The major impact factors for this difference are due to the optical losses, surface recombination, recombination in the space-charge region and rear contact effect

Methods

Results

Conclusion