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

Abstract

We present an electron selective passivating contact based on a tunneling SiO $_x$ 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 SiC $_x$ (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 °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 ( J0 ) of ∼8 and ∼4 fA/cm2. The SiC $_x$ (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 SiC $_x$ (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 SiC $_x$ (n). On p-type wafers, best V OC = 706 mV, FF = 80.2%, and J SC = 38.0 mA/cm2 with a final conversion efficiency of 21.5% are demonstrated for 2 × 2 cm2 screen-printed cells, with a simple and patterning-free process based on plasma depositions and one annealing step 800 °C T < 850 °C for the formation of both passivating contacts.