Development of a four sub-cell inverted metamorphic multi-junction (IMM) highly efficient AM0 solar cell

We have identified the IMM structure as the best vehicle to achieve increased AM0 solar cell efficiency beyond the conventional 3-junction lattice matched GaInP/GaAs/Ge architecture. Building on our efforts to develop a 3J-IMM III–V based cell presented at the 33
^rd
PVSC [1], we have developed a 4J-IMM AM0 solar cell. The top three sub-cells are identical to that incorporated in our 3J-IMM cell. The fourth sub-cell is composed of 0.70eV GaInAs. This cell structure required an extension of the transparent metamorphic (MM) buffer layer to accommodate an additional 2% mismatch, a metamorphic tunnel diode, and the fourth (MM) sub-cell‥ The processing steps to fabricate this cell are very similar to those previously discussed with regard to the 3J-IMM cell. At 28°C, our best CICed (cover-glass interconnected cell) 4J-IMM 2×2 cm
²
cell achieved a 33.9% AM0 (135.3 mW/cm
²
) efficiency.