Monitoring the high-efficiency silicon solar cell process by lifetime measurements

In this paper, the authors investigate the use of lifetime measurements as a tool to monitor high-efficiency silicon solar cell processes. Contactless lifetime measurements are carried out after every processing step for monocrystalline float zone wafers of resistivity 9.0 and 0.4 Ω cm and for polycrystalline silicon of small grain size. These measurements show that the lifetimes in lower resistivity wafers are subjected to degradation caused by thermal treatments. Indications that surface recombination is enhanced on textured surfaces (inverted pyramids and grooves) are also shown and these results are viewed in relation to the reflectance data on these surfaces. The effect of hydrogenation on the lifetime in small-grain polycrystalline silicon is studied for two conditions: hydrogenation under direct RF plasma; and hydrogenation using a PECVD silicon nitride layer as a source of hydrogen. Improvements in lifetime were found in both cases