FABRICATION AND ANALYSIS OF RECORD HIGH 18.2-PERCENT EFFICIENT SOLAR-CELLS ON MULTICRYSTALLINE SILICON MATERIAL

Solar cell efficiencies of 18.2% (1 cm(2) areas) have been achieved us ing a process sequence which involves impurity gettering on 0.65 Omega -cm multicrystalline silicon (me-Si) grown by the heat exchanger metho d (HEM), This represents the highest reported solar cell efficiency on me-Si to date, Photoconductive decay (PCD) measurements were used to monitor the lifetime in control samples which underwent the same proce ss sequence as solar cells, PCD analysis reveals that HEM me-Si materi al with an average as-grown bulk lifetime (tau(b)) of 12 mu s can achi eve a lifetime as high as 135 mu s by process-induced gettering, Inter nal quantum efficiency (IQE) measurements reveal that the effective di ffusion length (L(eff)) in the finished devices is 244 mu m (or close to 90% of the total device width). Detailed cell analysis shows that f or this combination of tau(b) and L(eff), the back surface recombinati on velocity (S-b) Of 10 000 cm/s or higher is the dominant efficiency limiting factor in the uniform regions of these me-Si devices, Lowerin g S-b Can raise the efficiency of untextured HEM me-Si solar cells abo ve 19.0%, thus closing the efficiency gap between good quality, untext ured single crystal and me-Si solar cells.