Development of manufacturing capability for high-concentration, high-efficiency silicon solar cells

This report presents a summary of the major results from a program to develop a manufacturable, high-efficiency silicon concentrator solar cell and a cost-effective manufacturing facility. The program was jointly funded by the Electric Power Research Institute, Sandia National Laboratories through the Concentrator Initiative, and SunPower Corporation. The key achievements of the program include the demonstration of 26%-efficient silicon concentrator solar cells with design-point (20 W/cm{sup 2}) efficiencies over 25%. High-performance front-surface passivations; that were developed to achieve this result were verified to be absolutely stable against degradation by 475 days of field exposure at twice the design concentration. SunPower demonstrated pilot production of more than 1500 of these cells. This cell technology was also applied to pilot production to supply 7000 17.7-cm{sup 2} one-sun cells (3500 yielded wafers) that demonstrated exceptional quality control. The average efficiency of 21.3% for these cells approaches the peak efficiency ever demonstrated for a single small laboratory cell within 2% (absolute). Extensive cost models were developed through this program and calibrated by the pilot-production project. The production levels achieved indicate that SunPower could produce 7-10 MW of concentrator cells per year in the current facility based upon the cell performance demonstrated during the program

On the use of a bias-light correction for trapping effects in photoconductance-based lifetime measurements of silicon

The effectiveness of a method for analytically reducing the effect of trapping centers on photoconductance-based recombination lifetime measurements in silicon is examined. The correction method involves the use of a ‘‘bias-light’’ term to subtract out the underlying photoconductance due to the traps. The technique extends, by approximately an order of magnitude, the range of carrier densities over which reasonably accurate (within 30%) measurements of the recombination lifetime can be made. Guidelines for determining which bias-light intensity will produce the best correction for solar grade multicrystalline silicon wafers, and the range over which it is valid, are developed for several practical cases

The Implementation of Temperature Control to an Inductive-Coil Photoconductance Instrument for the Range of 0-2308C

A new device setup for temperature and injection-dependent lifetime spectroscopy (TIDLS) is described. It comprises two off-the-shelf components: a heating and cooling stage (HCS) from INSTEC and an inductive-coil photoconductance (PC) instrument (WCT-100) from Sinton Consulting Inc. The HCS was fitted to the WCT-100 in a manner that circumscribes the inductive coil (the sensor) of the RF bridge circuit and controls the temperature of the wafer effectively. This setup has the advantage of requiring minor modifications to industry standard instruments while attaining a large temperature range. As experimental verification, injection-dependent lifetimes were measured over a temperature range, 0-230°C, in three iron-implanted silicon wafers. The measured lifetimes are consistent with the Shockley-Read-Hall equation using the impurity concentration calculated from the implant dose and the energy level and capture cross-sections of interstitial iron from the literature