Physical and Technological Aspects of a-Si:H/c-Si Hetero-Junction Solar Cells

We report on the basic properties of a-Si:H/c-Si hetero-junctions, their effects on the recombination of excess carriers and its influence on the a-Si:H/c-Si hetero-junction solar cells. For this purpose we measured the gap state density distribution in thin a-Si:H layers, determined its dependence on deposition temperature and doping by an improved version of near UV-photoelectron emission spectroscopy. Furthermore, the Fermi level position in the a-Si:H and the valence band offset were directly measured. In combination with interface specific methods such as surface photovoltage analysis and our numerical simulation program AFORS-HET, we are able to find out the optimum in wafer pretreatment, doping and deposition temperature for efficient a-Si:H/c-Si solar cells without an i-type a-Si:H buffer layer. By a deposition at 210degC with an emitter doping of 2000 ppm of B₂ H₆ on a well cleaned pyramidal structured c-Si(p) wafer we reached 19.8 % certified efficiency