  Multi-junction photovoltaics provide a logical method of increasing the
utilization of solar power for a given area. However, their current design and
fabrication methods invoke numerous material and cost complexities that limit
their potential, particularly for flat panel paradigms. In this paper, three
general strategies based on the electrical isolation of the internal sub-layers
are described. These strategies involve current or voltage matching the
sub-layers by varying of fractional absorption and areal coverage of individual
cells within each sub-layer, as well as modifying their combined output using
power electronics. A simplified theoretical description of these strategies is
provided for pairs of junction materials that allows a more streamlined
description of the requirements.

Optics