Hydrogen passivation of multicrystalline silicon solar cells

Abstract

The use of hydrogen for passivation of multicrystalline silicon in solar cell technology is described. Three kinds of hydrogen incorporation into mc-Si solar cells have been evaluated: hydrogen diffusion out of a SiN-layer (SiN:H), low-energy hydrogen ion implantation (HII), and remote plasma hydrogen passivation (RPHP). Best results were obtained by RPHP, whereas using HII, damage exceeded the passivation effect to some extent. While SiN:H passivates more the grains, RPHP acts particular on grain boundaries. Combining hydrogen passivation by SiN:H and RPHP leads to optimal bulk passivation. We have investigated the influence of RPHP to various mc-Si materials by solar cell and diffusion length measurements. CVD layers and ribbon material show the strongest increase in performance. A boost of up to 77.0 mV in the open-circuit voltage and 2.0% in the efficiency of solar cells has been achieved. Electromagnetically casted Si has shown an improvement of 2.1% in efficiency after RPHP treatment. But even mc-Si of higher quality, like mc-Baysix and Eurosolare mc-Si could be rectified by RPHP. Applying a standard cell process for material assessment efficiencies of 16.9% have been obtained including a RPHP step. Thus the potential for high-efficiency mc-Si solar cells is shown.