High-throughput zone-melting recrystallization for crystalline silicon thin-film solar cells

Crystalline silicon thin-film solar cells which shall exceed a conversion efficiency of 15% require a coarse-grained silicon layer of at least 5 μm thickness as an absorber layer, with minority carrier diffusion length and grain diameter at least twice the layer thickness. At Fraunhofer ISE, we use zone-melting recrystallization to recrystallize a silicon layer grown by chemical vapor deposition on high-temperature stable substrates. Our main focus is the development of tools and processes for achieving silicon layers of sufficient electrical quality at high throughput and low cost. A processor for in-line zone melting of 400-mm-wide samples was developed, which has gas curtain load locks and thus offers a theoretical maximum throughput of approx. 10 m2/h at a melting velocity of 500 mm/min. Zone-melting experiments with varying melting velocity showed that high crystal quality can be maintained even for velocities up to 350 mm/min.