3D Distributions of Chlorine and Sulphur Impurities in a Thin-Film Cadmium Telluride Solar Cell
- PDF / 1,071,674 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 2 Downloads / 189 Views
MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.449
3D Distributions of Chlorine and Sulphur Impurities in a Thin-Film Cadmium Telluride Solar Cell Thomas A. M. Fiducia1, Kexue Li2, Amit H. Munshi3, Kurt Barth3, Walajabad S. Sampath3, Chris R. M. Grovenor2, John M. Walls1. 1
Loughborough University, Loughborough, Leicestershire, LE11 3TU, United Kingdom
2
Materials Department, Oxford University, Oxford, OX1 3PH, United Kingdom
3
Colorado State University, Fort Collins, Colorado, 80523, USA
ABSTRACT
A cadmium chloride activation treatment is essential for the production of high efficiency cadmium telluride (CdTe) solar cells. However, the effects of the treatment on the distributions of chlorine and sulphur within the device are not fully understood. Here, the detailed locations of chlorine and sulphur in a treated CdTe cell are determined in three dimensions by high resolution dynamic SIMS measurements. Chlorine is found to be present in grain boundaries, grain interiors, extended defects within the grain interiors, at the front interface, and in the cadmium sulphide layer. In each of these regions, the chlorine is likely to have significant effects on local electronic properties of the material, and hence overall device performance. Sulphur is found to have a U-shaped diffusion profile within CdTe grains, indicating a mixed grain boundary and lattice diffusion regime.
INTRODUCTION Chlorine and sulphur are known to affect the electronic behaviour of CdTe locally. Chlorine pacifies grain boundaries, affects doping, and can alter the bandstructure of CdTe [1] [2] [3]. Sulphur alters the material’s bandgap - affecting light absorption and carrier transport - and can affect material microstructure [4]. It is therefore important that the location and distributions of the two elements within the device are known. However, their behaviour during the ubiquitous cadmium chloride (CdCl2) heat treatment is complex. For instance, chlorine segregates to grain boundaries in the CdTe, and sulphur is known to interdiffuse into the CdTe layer [5][4]. Secondary Ion Mass Spectrometry (SIMS), specifically high resolution dynamic SIMS (NanoSIMS), is an ideal characterisation technique for monitoring these complex behaviours because of its high sensitivity and spatial resolution, and its ability to produce 3D data (detection limits are µg g-1 or lower for most elements, and resolution is sub 100 nm [6]) . In this work, high resolution 3D dynamic SIMS measurements are performed
Downloaded from https://www.cambridge.org/core. University of Pennsylvania Libraries, on 28 May 2018 at 02:28:42, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2018.449
on a CdS/CdTe solar cell to obtain a complete analysis of the locations of chlorine and sulphur in the device. This can then be used to inform processing changes to improve cell performance. EXPERIMENTAL A plate of cadmium telluride devices was fabricated in an all-in-one vacuum process at
Data Loading...
