Status of amorphous silicon alloy solar cells and modules made near the onset of microcrystallinity

Amorphous silicon (a-Si) alloy solar cells made near the onset of micro-crystallinity exhibit superior characteristics. The amorphous to microcrystalline transition depends critically on the hydrogen dilution used during the film growth and the cell thickness. Cell open-circuit voltage (V_oc) was used to determine the transition threshold for various hydrogen dilutions. Devices made on the transition edge exhibit a significant reduction in V_oc and a dispersion of its values due to nonuniform microcrystallite inclusions in an amorphous matrix. The best cells are made in the amorphous region just below the threshold. Status of a-Si and a-SiGe alloy component cells suitable for use in high efficiency triple-junction devices is presented. Using near threshold conditions, a large-area (~922cm²) fully encapsulated triple-junction module with an initial aperture-area efficiency of 11.9% has been achieved and confirmed by NREL