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

Solar cell efficiencies of 18.2% (1 cm² areas) have been achieved using a process sequence which involves impurity gettering on 0.65 Ω-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 (τ_b) of 12 μs can achieve a lifetime as high as 135 μs by process-induced gettering. Internal quantum efficiency (IQE) measurements reveal that the effective diffusion length (L_eff) in the finished devices is 244 μm (or close to 90% of the total device width). Detailed cell analysis shows that for this combination of τ_b and L_eff, the back surface recombination velocity (S_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_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