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Investigations of parasitic shunt resistance in n‐type buried contact solar cells

It has been shown that n‐type laser‐grooved buried contact solar cells exhibit a high‐efficiency potential, both on interdigitated backside buried contact (IBBC) and double‐sided buried contact (DSBC) cell structures. As the IBBC solar cell contains heavily doped, compensated regions, the shunt mechanisms are more complicated, and are different from those of the conventional front‐collecting‐junction solar cells. In this paper, several shunting mechanisms hindering the performances of the n‐type buried contact solar cells are investigated and discussed. The main shunting routes in n‐type IBBC solar cells are concluded as follows: (1) the emitter contact metal touching the n‐type substrate, which is either due to nonuniform boron deposition or diffusion‐induced misfit dislocations; (2) the base contact metal touching the p+ emitter, attributed to either the phosphorus groove diffusion being unable to compensate for the boron emitter diffusion, or the junction depth located in the diffusion overlap regions not deep enough to prevent nickel from spiking through the groove diffusion. The shunt resistance of the IBBC cells increased by more than two orders of magnitude after eliminating the shunt mechanisms discussed in this study. This led to an improvement in fill factor from 0·71–0·73 to 0·74–0·76, and an increase of average absolute efficiency of more than 0·65%. Copyright © 2005 John Wiley & Sons, Ltd.