Optical and electrical characterization of poly-Si/SiOx contacts and their implications on solar cell design

The scope of this paper lies on the phenomenon of free-carrier absorption (FCA) in heavily phosphorus-doped poly-Si layers, applied at solar cells featuring poly-Si/SiO x passivating contacts at the rear. Firstly, FCA is investigated on test structures featuring poly-Si contacts of different thickness and doping level. Secondly, these passivating contacts are integrated into the rear of solar cells featuring a boron-diffused emitter at the front. The infrared (IR) response of the solar cells is analyzed and FCA losses are quantified. In agreement with theory, it is shown that J sc losses due to FCA increase with poly-Si doping level and thickness. For instance, a total J sc loss of ~0.5 mA/cm² is obtained for a 145 nm thick poly-Si layer with a doping concentration of 1.9x10 20 cm -3 .