Thick-emitter silicon solar cells

Some results of a theoretical optimization of the emitter region of a silicon solar cell are presented. The best compromise between recombination current, quantum collection efficiency, and sheet resistance is found for relatively thick, moderately doped, surface-passivated emitters. Experimental evidence is given to support the thick-emitter philosophy. Efficiencies up to 19.1% (global AM1.5) and open-circuit voltages up to 670 mV (25 degrees C) have been measured in 2*2 cm² cells having a textured surface, a single-layer antireflection coating, and a 7% grid shadowing. Even though the junction depth is between 0.8 and 2.4 mu m, the internal quantum efficiency is still high, ranging from 91% to 75% for lambda =400 nm. The experiments include a determination of the influence of the metal grid coverage factor on open-circuit voltage, leading to the prediction of a high-voltage (660 mV) and high-efficiency (18.6%) capability for such an industrial metallization technology as screen printing.