Regulation of Substrate-Target Distance on the Microstructural, Optical and Electrical Properties of CdTe Films by Magnetron Sputtering.

Peng Gu,Dingyu Yang,Haihua Wu,Xinghua Zhu

doi:10.3390/ma11122496

Peng Gu, Dingyu Yang + Show 2 more

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https://doi.org/10.3390/ma11122496

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Abstract

Cadmium telluride (CdTe) films were deposited on glass substrates by direct current (DC) magnetron sputtering, and the effect of substrate-target distance (Dts) on properties of the CdTe films was investigated by observations of X-ray diffraction (XRD) patterns, atomic force microscopy (AFM), UV-VIS spectra, optical microscopy, and the Hall-effect measurement system. XRD analysis indicated that all samples exhibited a preferred orientation along the (111) plane, corresponding to the zinc blende structure, and films prepared using Dts of 4 cm demonstrated better crystallinity than the others. AFM studies revealed that surface morphologies of the CdTe films were strongly dependent on Dts, and revealed a large average grain size of 35.25 nm and a high root mean square (RMS) roughness value of 9.66 nm for films fabricated using Dts of 4 cm. UV-VIS spectra suggested the energy band gap (Eg) initially decreased from 1.5 to 1.45 eV, then increased to 1.68 eV as Dts increased from 3.5 to 5 cm. The Hall-effect measurement system revealed that CdTe films prepared with a Dts of 4 cm exhibited optimal electrical properties, and the resistivity, carrier mobility, and carrier concentration were determined to be 2.3 × 105 Ω∙cm, 6.41 cm2∙V−1∙S−1, and 4.22 × 1012 cm−3, respectively.

Highlights

In recent years, silicon (Si) has been considered as the most important material for preparing film-form solar cells, due to its well-established preparation process and its theoretical conversion efficiency of Si-based solar cells being approximately 25% [1,2]
cadmium telluride (CdTe) films were successfully deposited on glass substrates by direct-current magnetron sputtering
CdTe films were successfully deposited on glass substrates by direct-current magnetron technology, and the effect of sputtering distance on the structural, morphological, optical and electrical sputtering technology, and the effect of sputtering distance on the structural, morphological, optical properties of CdTe films were investigated and discussed

Summary

Introduction

Silicon (Si) has been considered as the most important material for preparing film-form solar cells, due to its well-established preparation process and its theoretical conversion efficiency of Si-based solar cells being approximately 25% [1,2]. Si is not an optimal candidate for the fabrication of high-performance film-form solar cells. Due to their suitable energy band gap (1.45 eV) and high absorption coefficient (>105 cm−1 in the visible range), CdTe films demonstrate distinctive merit among photovoltaic materials and achieve high photoelectric conversion performance, with a film thickness of only 1~2 μm [5,6,7,8]. Some studies have proved that pinholes often appear on the surface of CdTe films and result in a leakage current, which increase the recombination rate of carriers in the pinhole defects, leading to a decrease in the filling factor (FF) and open-circuit voltage (Voc ) [9,10]. If the thickness of such films exceeds the diffusion length of the carriers, recombination of electron-hole pairs becomes significant and results in Materials 2018, 11, 2496; doi:10.3390/ma11122496 www.mdpi.com/journal/materials

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