Comparison of back interface structure alternatives using two sided optical excitation

The back interface of a solar cell is an important part of the device structure, providing several important functions: 1) reduces the effective surface recombination velocity, therefore raises both the short circuit current and Voc; 2) it may contain a high-low junction which adds it´s own contribution to the Voc and Vmax; 3) provides a low resistance ohmic contact. An added optical effect includes reflectance of long wavelength light back into the semiconductor not absorbed on the first pass through the material. The most common back interface structure is a “back surface field” created by a high - low junction. Others include a passivated surface using dielectrics such as SiO2, SiN, or Al2O3, a floating junction inbetween localized contacts, and a local BSF where a h-l junction is present between passivated regions. This paper focuses on the contribution to Voc made by the h-l junction.