Record high 18.6% efficient solar cell on HEM multicrystalline material

Solar cells with efficiencies as high as 18.6% (1 cm/sup 2/ area) have been achieved by a process which involves impurity gettering and effective back surface passivation on 0.65 /spl Omega/-cm multicrystalline silicon (mc-Si) grown by the heat exchanger method (HEM). This represents the highest reported solar cell efficiency on mc-Si to date. PCD analysis revealed that the bulk lifetime (/spl tau//sub b/) in HEM samples after phosphorus gettering can be as high as 135 /spl mu/s. This increases the impact of the back surface recombination velocity (S/sub b/) on the solar cell performance. By incorporating a deeper aluminum BSF, the S/sub b/ for solar cells in this study was lowered from 10000 cm/s to 2000 cm/s on HEM mc-Si. This combination of high /spl tau//sub b/ and moderately low S/sub b/ resulted in the record high efficiency mc-Si solar cell. Model calculations indicate that lowering S/sub b/ further can raise the efficiency of untextured HEM mc-Si solar cells above 19.0%, thus closing the efficiency gap between good quality, untextured single crystal and mc-Si solar cells.