AVS 61st International Symposium & Exhibition
    Energy Frontiers Focus Topic Wednesday Sessions
       Session EN+AS+EM+SE-WeM

Paper EN+AS+EM+SE-WeM13
Micro-Structural Activation Mechanisms in Thin Film CdTe Photovoltaic Devices

Wednesday, November 12, 2014, 12:00 pm, Room 315

Session: Thin Film Photovoltaics
Presenter: John Walls, Loughborough University, UK
Authors: J.M. Walls, Loughborough University, UK
A. Abbas, Loughborough University, UK
J.W. Bowers, Loughborough University, UK
P.M. Kaminski, Loughborough University, UK
K. Barth, Colorado State University
W. Sampath, Colorado State University
Correspondent: Click to Email
Thin Film CdTe photovoltaics is a commercially successful second generation technology now used extensively in solar energy generation at the utility scale. Although the cadmium chloride treatment is a process that is essential to produce high efficiency devices, the precise mechanisms involved in the re-crystallization and associated improvement in electronic properties have not been fully understood. In this paper we report on the application of advanced micro-structural characterization techniques to study the effect of the cadmium chloride treatment on the physical properties of the cadmium telluride solar cell deposited by both close space sublimation (CSS) and magnetron sputtering and relate these observations to device performance. In particular, High Resolution Transmission Electron Microcopy (HRTEM) reveals that the untreated material contains high densities of planar defects which are predominantly stacking faults and that the optimized cadmium chloride treatment removes these completely with only twins remaining. Parallel theoretical studies using Density Functional Theory (DFT) shows that certain types of stacking fault are responsible for the poor performance of the untreated material. Extending the treatment time or increasing the annealing temperature above ~4000C improves the microstructure but results in lower efficiency devices. Composition –depth profiling using XPS and SIMS reveals that this deterioration in performance is linked with chlorine build up at the CdS/CdTe junction. These experiments and parallel theoretical studies have improved our understanding of the mechanisms at work in the cadmium chloride assisted re-crystallization of CdTe and could lead to further increases in device efficiency