Characterization of dielectric layer, laser damage and edge recombination in miniature silicon solar cells

Miniature silicon solar cells (8 × 2.0 mm²) are being fabricated for use in tandem-cell concentrator systems. Several factors combine to make the achievement of high efficiency problematical. These include surface, bulk and edge recombination. The latter is relatively important because the surface area of the edge of a small cell is a large fraction of the total surface area. Surface recombination in the cells is caused by the loss of passivating hydrogen beneath a conformal LPCVD SiNx coating, induced by high temperature annealing. Bulk carrier lifetime degradation mechanisms that we have encountered include silicon crystal damage induced by laser scribing of the cells, which affects a relatively large proportion of the volume of the cell. The Quasi-steady state photoconductance (QSSPC) measurement technique was used for the carrier lifetime degradation study. Firstly, a detailed study was undertaken of the carrier lifetime degradation due to the loss of hydrogen in conformally deposited LPCVD silicon nitride grown samples and the effect of hydrogenation on these layers, when subjected to various anneal times and temperatures. Additionally, LPCVD nitride was studied to determine whether it can be used as a layer that can prevent or resist possible contamination, induced by prolonged high temperature anneals. Secondly, a comparison was made between reference samples and samples that were exposed to laser scribing and dicing to determine whether laser scribing is suitable for the shaping of miniature silicon solar cells. Finally, cells with different pn junction designs were fabricated and tested to study edge recombination.