PROGRESS IN MULTIJUNCTION AMORPHOUS-SILICON ALLOY-BASED SOLAR-CELLS AND MODULES

We have achieved an initial efficiency of 11.4% as confirmed by the National Renewable Energy Laboratory (NREL) on a multijunction amorphous silicon alloy photovoltaic module of one-square-foot area. This is the highest initial efficiency confirmed by NREL for any thin film photovoltaic module. After light soaking for 1000 h at 50 degrees C under one-sun illumination, a module with initial efficiency of 11.1% shows a stabilized efficiency of 9.5%. The improvement in module efficiency has been achieved by: (i) improving the performance of the component cells of the multijunction structure, (ii) optimizing the ''tunnel'' junction between the component cells, (iii) obtaining a better uniformity of the deposited layers over one-square-foot area, and (iv) reducing module losses.