Effect of the composition on physical properties of CdTe absorber layer fabricated by chemical molecular beam deposition for use in thin film solar cellsWe explore Cu electronic states in CdTe using photoluminescence as the main investigative method. Our results are consistent with some Cu atoms occupying substitutional positions on the Cd sublattice and with others forming Frenkel pairs of the type Cu i ϩ -V Cd Ϫ involving an interstitial Cu and a Cd vacancy. In addition, we find that Cu-doped CdTe samples exhibit a significant ''aging'' behavior, attributable to the instability of Cu acceptor states as verified by our Hall measurements. The aging appears to be reversible by a 150-200°C anneal. Our results are used to explain efficiency degradation of some CdTe solar-cell devices which use Cu for the formation of a backcontact.
SunPower is currently shipping the highest efficiency commercial solar panel in the 20% efficiency E-series with high reliability, and proven high energy yield per rated watt [1,2]. This paper discusses the next generation SunPower solar cell, the Maxeon Gen III used in the recently launched X-series modules. Higher efficiency, improved field performance from lower temperature coefficient, improved reliability due to low reverse breakdown voltage and a uniform dark appearance are the characteristics of this technology. The SunPower Maxeon Gen III solar cell is a high efficiency design intended to reduce cost throughout the value chain by improved performance. The improved efficiency is due to a passivated contact structure lowering the cell emitter recombination to approximately 15 fA/cm 2 [3]. The process is currently in full scale manufacturing at approximately 100 MW per year in the SunPower's Fab2 production facility in the Philippines.
The preparation and characterization of NiTe 2 back contacts to CdTe/CdS cells are described. NiTe 2 is formed on p-CdTe by electroless deposition at low reductant concentrations, producing devices that are superior ͑conversion efficiencies often exceeding 10%͒ to those contacted with electroless Ni. X-ray photoelectron spectroscopy and X-ray diffraction showed the product to be nickel͑II͒ ditelluride (Ni 2ϩ Te 2 2Ϫ), produced, in the catalytic presence of Al 3ϩ ions, by the reaction of Ni 2ϩ ions with a Te-rich CdTe surface, which is formed by an in situ etch in the chemical bath. Preliminary results indicate that Ni, from NiTe 2 , is not mobile within the cell structure, which is expected to be favorable for stability. Cells exhibit degradation when exposed to H 2 O vapor. However, this effect was found to be reversible, with performance improving to near predegradation values following cell transfer to dry air conditions.
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