Fabrication and analysis of record high 18.2% efficient solar cells on multicrystalline silicon material

Abstract

Solar cell efficiencies of 18.2% (1 cm/sup 2/ areas) have been achieved using a process sequence which involves impurity gettering 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. Photoconductive decay (PCD) measurements were used to monitor the lifetime in control samples which underwent the same process sequence as solar cells. PCD analysis reveals that HEM mc-Si material with an average as-grown bulk lifetime (/spl tau//sub b/) of 12 /spl mu/s can achieve a lifetime as high as 135 /spl mu/s by process-induced gettering. Internal quantum efficiency (IQE) measurements reveal that the effective diffusion length (L/sub eff/) in the finished devices is 244 /spl mu/m (or close to 90% of the total device width). Detailed cell analysis shows that for this combination of /spl tau//sub b/ and L/sub eff/, the back surface recombination velocity (S/sub b/) of 10 000 cm/s or higher is the dominant efficiency limiting factor in the uniform regions of these mc-Si devices. Lowering S/sub b/ 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.