Feasibility study for silicon heterojunction metal wrap through (SHJ-MWT) solar cells

Silicon heterojunction solar cells with efficiencies of up to 24.7 % can be further improved by introducing a metal wrap through metallization. However, silicon heterojunction metal wrap through solar cells suffer from specific loss mechanisms caused by the non-conformal amorphous silicon emitter. The critical mechanisms are resistive and recombination losses in the via. In this work, the recombination at the poorly passivated via surfaces is described theoretically and verified by spatially resolved lifetime measurements using microwave detected photoconductivity. Based on this model, it is shown that the current loss due to via recombination is negligible. However, resistive losses are very critical. A direct electric contact of via metallization and silicon base potentially shunts the cell. To suppress this shunt path, it is suggested to realize the silicon heterojunction metal wrap through solar cell as a back junction cell. In this configuration, the insulation of both contacts becomes very similar to the sequence applied in standard homojunction metal wrap through solar cells. Furthermore, the back junction configuration has the potential for higher efficiencies. AFORS HET simulations show that silicon heterojunction cells could gain up to 3 mA/cm2 in photocurrent when shifting the emitter from front to back side and introducing a dielectric front side passivation.