Strain-balanced materials for high-efficiency solar cells

Traditionally, monolithic multi-junction solar cells have required lattice matched material combinations for efficient operation. However, strain-balanced structures allow lattice mismatched materials to be grown pseudomorphically, with low defect densities, and therefore offer interesting band-gap configurations for attaining optimal multi-junction solar cell structures. Several material combinations are identified and their suitability as highly efficient photovoltaic materials discussed; in particular InxGa1-xAs, GaAs1-xPx, GaInP and GaInNAs. Estimates for the limiting efficiency of strain-balanced multi-junction cells are presented, together with an outline of the technological requirements to achieve such cells