Phosphorous-Doped Silicon Carbide as Front-Side Full-Area Passivating Contact for Double-Side Contacted c-Si Solar Cells

摘要

We present an electron selective passivating contact based on a tunneling SiOx capped with a phosphorous doped silicon carbide and prepared with a high-temperature thermal anneal. We investigate in detail the effects of the preparation conditions of the SiCx (n) (i.e., gas flow precursor and annealing temperature) on the interface recombination rate, dopant in-diffusion, and optical properties using test structures and solar cells. On test structures, our investigation reveals that the samples annealed at temperatures of 800-850 degrees C exhibit an increased surface passivation toward higher gas flow ratio (r = CH4/(SiH4 + CH4)). On textured and planar samples, we obtained best implied open-circuit voltages (i-V-OC) of 737 and 746 mV, respectively, with corresponding dark saturation current densities (J(0)) of similar to 8 and similar to 4 fA/cm(2). The SiCx (n) layers with different r values were applied on the textured front side of p-type c-Si solar cells in combination with a boron-doped SiCx(p) as rear hole selective passivating contact. Our cell results show a tradeoff between V-OC and short-circuit current density (J(SC)) dictated by the C-content in the front-side SiCx (n). On p-type wafers, best V-OC = 706 mV, FF = 80.2%, and J(SC) = 38.0 mA/cm(2) with a final conversion efficiency of 21.5% are demonstrated for 2 x 2 cm(2) screen-printed cells, with a simple and patterning-free process based on plasma depositions and one annealing step 800 degrees C < T < 850 degrees C for the formation of both passivating contacts.