Center for Renewable Energy Systems and Technology

Loughborough, United Kingdom

Center for Renewable Energy Systems and Technology

Loughborough, United Kingdom
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Walls J.M.,Center for Renewable Energy Systems and Technology | Abbas A.,Center for Renewable Energy Systems and Technology | Abbas A.,Loughborough University | West G.D.,Loughborough University | And 6 more authors.
Materials Research Society Symposium Proceedings | Year: 2013

It is well known that the cadmium chloride annealing treatment is an essential step in the manufacture of efficient thin film cadmium telluride solar cells. It has been recognized that the combination of annealing at ∼4000C together with the addition of cadmium chloride at the surface induces re-crystallisation of the cadmium telluride layer and also affects the n-type cadmium sulfide. We have applied advanced micro-structural characterization techniques to distinguish the effect of the annealing and the cadmium chloride treatments on the properties of the cadmium telluride deposited via close space sublimation (CSS) and relate these observations to device performance. Transmission electron microscopy (TEM) has shown a variation in stacking fault density with annealing temperature and annealing time. Stacking faults observed within the cadmium telluride grains in TEM were partially removed post annealing; these findings show that temperature alone has a role in the reduction of stacking faults. However, since we have previously observed almost complete removal of stacking faults with annealing in combination with cadmium chloride, the cadmium chloride is essential to defect removal and high efficiency cells. © 2012 Materials Research Society.


Abbas A.,Loughborough University | Abbas A.,Center for Renewable Energy Systems and Technology | West G.D.,Loughborough University | Bowers J.W.,Center for Renewable Energy Systems and Technology | And 5 more authors.
Conference Record of the IEEE Photovoltaic Specialists Conference | Year: 2013

The aim of this investigation is to apply advanced microstructural characterization techniques to study the effects of varying the cadmium chloride annealing temperature on the microstructure of cadmium telluride solar cells deposited by close spaced sublimation (CSS) and relate this to cell performance. A range of techniques have been used to observe the morphological changes to the microstructure as well as the chemical and crystallographic changes as a function of treatment parameters. Electrical tests that link the device performance with the microstructural properties of the cells have also been undertaken. Techniques used include Transmission Electron Microscopy (TEM) for sub-grain analysis, X-ray Photoelectron Spectroscopy (XPS) depth profiles to show the effect of temperature on the diffusion of chlorine into the CdTe. Grain orientation data as well as grain size change has been obtained using Electron Backscatter Diffraction (EBSD) on Focused Ion Beam (FIB) prepared planar sections. © 2013 IEEE.


Abbas A.,Center for Renewable Energy Systems and Technology | Kaminski P.,Center for Renewable Energy Systems and Technology | West G.,Loughborough University | Barth K.,Colorado State University | And 3 more authors.
Materials Research Society Symposium Proceedings | Year: 2015

The cadmium chloride annealing treatment is an essential step in the manufacture of efficient thin film CdTe solar cells. In previous work we have shown that the primary effect of the treatment is to remove high densities of stacking faults from the as-deposited material. Use of density functional theory has shown that some of the higher energy stacking faults are hole traps. Removal of these defects dramatically improves cell efficiency. In this study we focus on the effect of the activation treatment on the underlying n-type cadmium sulphide layer. A range of techniques has been used to observe the changes to the microstructure as well as the chemical and crystallographic changes as a function of treatment parameters. Electrical tests that link the device performance with the micro-structural properties of the cells have also been undertaken. Techniques used include High Resolution Transmission Electron Microscopy (HRTEM) for subgrain analysis, EDX for chemical analysis and XPS and SIMS for composition-depth profiling. By studying the effect of increasing the treatment time and temperature, we will show that the cadmium sulphide layer depletes to the point of complete dissolution into the absorber layer. We will also show that chlorine penetrates and decorates the grain boundaries in the cadmium sulphide. In addition we will show that chlorine builds up at the heterojunction and concentrates in voids at the cadmium telluride/cadmium sulphide interface. A combination of these effects damages the electrical performance of the solar cell. © 2015 Materials Research Society.

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