High efficiency inline diffused emitter (ILDE) solar cells on mono-crystalline CZ silicon

High throughput, low cost, and high efficiency are the keys to reducing the cost of photovoltaic electricity. To realize high efficiency, the quality of emitter is critical. The emitter can be formed either by batch deposition in a tube using liquid POCl(3) source or by inline spray deposition of phosphoric acid (P(2)O(5)). The POCl(3) process has been optimized over the years to give reproducible performance, whereas the inline diffusion has not been systematically optimized. This paper reports on solar cell results with the inline emitters. Sheet resistance mapping tool has been used to quantify the emitter uniformity in conjunction with junction depth and phosphorus surface concentration to characterize the inline emitters. We have achieved average efficiencies of 17.1 and 17.4%, respectively, on 2 Omega-cm textured CZ with 45 and 60 Omega/sq emitters. Average fill factor of 0.772 and ideality factor of 1.06 support the front contact firing optimization for the inline emitters. Personal computer one dimensional (PC ID) modeling of the 60 Omega/sq emitter showed efficiency of >18% is achievable by reducing the front surface recombination velocity (FSRV) from 120 000 to 80 000 cm/s and increasing the fill factor to 79.5%. Copyright (C) 2010 John Wiley & Sons, Ltd.