WCT-120 Wafer Lifetime & Suns-Voc Curve Tracer Tools

The WCT-120 is a tabletop silicon lifetime and wafer metrology system, suitable for both device research and industrial process control. It can be used for monitoring multicrystalline wafers, dopant diffusions, and low-lifetime samples. This method complements the use of the transient photoconductance technique that is also standard on this instrument. It also yields the implied open-circuit voltage (versus illumination) curve, which is comparable to an I-V curve at each stage of a solar cell process. The Suns-Voc stage is used for measuring wafers after Al firing, and then again after front-grid firing. This allows the optimization and monitoring of these steps to maintain voltage, obtain good ohmic contacts, and avoid shunting. By either probing the p+ and n+ regions directly or probing the metallization layer (if present), the Illumination-Voc curve can be measured. This curve can be displayed as a Suns-Voc plot or in the form of a standard photovoltaic curve which can be used to characterize shunting. The entire curve is measured at open circuit, so it is free from the effects of series resistance.