PHOTOVOLTAGE METHOD EMPLOYED FOR MONITORING OF SILICON SOLAR CELL TECHNOLOGY

摘要

The monitoring of c-Si wafer quality and cell production technology is the main purpose of this work. To characterize the silicon material during the process of the cell preparation, diffusion length of minority carriers Lwas chosen. The wavelength dependence of modified surface photovoltage (SPV) experiment was used as a cheapand reliable method of its evaluation. The SPV spectra of wafers for solar cells after etching of only a fewmicrometers (less than 20 μm) show a broadening of spectral response towards the IR region, which is probablycaused by some kind of structural defects formed as a consequence of Si ingots slicing. Successive etching removingup to 65 μm thick layer (from each side) was performed pointing out that for some wafers only such a deep etchingwas enough to remove totally the defect layer resulting in a smooth curve yielding standard diffusion length L about300 μm. On the other hand, neither the samples with p-n junction created onto the wafers not etched enough showpresence of SPV broadening effect. The SPV spectrum is consequently not deformed but the short diffusion lengthevaluated gives evidence of possible deep recombination center formation.in the subsurface layer. Quite deep etchingof sawn-off wafers or annealing in atomic hydrogen atmosphere is proved to prevent shortening of diffusion lengthand when keeping the surface recombination velocities low enough, to reach higher efficient solar cells.