Lifetime monitoring and hydrogen passivation in a buried contact cell process using String Ribbon silicon

Abstract

The buried contact cell design has a higher efficiency potential than the widely used screen print cell concept due to its selective emitter design and low shading losses. In industry only Cz-Si is used. Hydrogen bulk passivation and thermal load of the wafers are different in the buried contact process and can be key issues to reach high efficiencies with multi-crystalline silicon. Adjacent String Ribbon wafers are used to monitor the change of bulk lifetime during a buried contact process. Bulk lifetime was measured 2-dimensionally resolved with μ-PCD. An improvement of PECVD-SiN deposition without a firing step was measured. The heavy 10 Ohm/sq diffusion leads to a degradation due to effusion of hydrogen. Bulk lifetime after hydrogen passivation by MIRHP in a buried contact solar cell process is similar to an adjacent wafer after a screen print process, therefore higher efficiencies of buried contact cells are expected.