Detecting driving potentials at the buried SiO₂ nanolayers in solar cells by chemical-selective nonlinear x-ray spectroscopy

We present an approach to selectively examine an asymmetric potential in the buried layer of solar cell devices by means of nonlinear x-ray spectroscopy. Detecting second harmonic generation signals while resonant to the SiO₂ core level, we directly observe existence of the band bending effect in the SiO₂ nanolayer, buried in the heterostructures of Al/LiF/SiO₂/Si, TiO₂/SiO₂/Si, and $Al 2 O 3$/SiO₂/Si. The results demonstrate high sensitivity of the method to the asymmetric potential that determines performance of functional materials for photovoltaics or other optoelectronic devices.