Analysis of the current linearity at low illumination of high-efficiency back-junction back-contact silicon solar cells

The relation between current and illumination intensity of three structures of high-efficiency back-junction back-contact silicon solar cells was analyzed. Both, n-type cells with non-diffused front surface and p-type cell with floating n-emitter show a pronounced non-linearity due to strong illumination dependence of the passivation quality of the non-diffused surface and the floating junction respectively. Quantum efficiency (QE) of this cell type drops significantly for the illumination lower than 0.5 suns. In contrast the QE of n-type cells with n(+)-front surface field (FSF) is linear. Low illumination current characteristics of all three of the analyzed structures could be well described by physical models.