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Increased Efficiency with CdSeTe Layer in Front of CdTe
J.R. Sites, A. Huss, T. Song, M. Lingg
Cadmium Telluride, Solar Cells, band structure
Non Silicon-Based Thin Film Photovoltaics
Subtopic: CI(G)S, CdTe and Related Thin Film Solar Cells and Modules
Event: 35th European Photovoltaic Solar Energy Conference and Exhibition
Session: 3CO.8.1
843 - 845
ISBN: 3-936338-50-7
Paper DOI: 10.4229/35thEUPVSEC20182018-3CO.8.1
0,00 EUR
Document(s): paper


The highest-efficiency CdTe cells at both First Solar and Colorado State University have been made with a layer of the lower band-gap CdSeTe alloy between the emitter and the CdTe. Simulations which include the CdSeTe layer are in agreement with experimental results. The CdSeTe thickness has generally been the order of 1 μm. Most of the solar spectrum is therefore absorbed in the CdSeTe layer, which means that the cell structure is best described as a CdSeTe absorber with CdTe behind to form a back surface field. For Se/Te ratios between 0.1 and 0.4, the band gap decreases from 1.50 eV for CdTe to the neighborhood of 1.4 eV for the alloy. This decrease in band gap implies an increase in current density of approximately 3 mA/cm2, which is quite close to the amount seen experimentally. The voltage in both simulation and experiment for a single-layer CdSeTe absorber decreases by an amount similar to the 100-meV band-gap difference, but recovers to very nearly the same voltage as the CdTe cell when the CdSeTe/CdTe combination is employed. This recovery is strongly suggestive of a conduction-band offset near 100 meV that creates a back-surface field which reflects electrons at the CdSeTe/CdTe transition. The result demonstrates that the CdTe voltage deficit compared to the ideal can be reduced by approximately the 100-meV difference between the CdSeTe and CdTe band gaps and explains why an increase in absolute efficiency of approximately 2% has been observed.