Limited influence of grain boundary defects in hot-wire CVD polysilicon films on solar cell performance

Grain boundary defects in poly-Si:H films have been analysed by infrared spectroscopy, photo thermal deflection spectroscopy, dual beam photoconductivity and electron spin resonance techniques. Complete absence of 2100 cm-1 mode in infrared spectrum is observed in a material with a low defect concentration. The dangling bond resonance line at g = 2.0055 showed narrowing (temperature-independent) with increasing defect density in the material. The narrowing is attributed to Heisenberg exchange at clustered defects. The transport path in a cell is through the grains and the carrier transport bypasses these grain boundary defects. This bypass explains why our n-i-p cell incorporating a 1.5-μm poly-Si:H i-layer generates a current of 18.2 mA cm-2 even though the defect density is 7.8 X 1016 cm-3. © 1998 Elsevier Science B.V. All rights reserved.