Inverted Metamorphic III–V Triple-Junction Solar Cell with a 1 eV CuInSe2 Bottom Subcell

A new triple-junction solar cell (3J) design exploiting the highly absorptive I–III–VI chalcopyrite CuInSe2 material is proposed as an alternative to III–V semiconductor 3J solar cells. The proposed structure consists of GaInP (1.9 eV)/Ga(In)As (1.4 eV)/CuInSe2 (1 eV) which can be grown on a GaAs substrate in an inverted manner using epitaxial lift-off techniques. To lattice-match epitaxial CuInSe2 to Ga(In)As, a compositionally graded buffer region composed of GaxIn1−xP is used. The modeling and simulation of the device include the effects of threading dislocations on minority carrier lifetimes in the metamorphic buffer and bottom subcell active region. Studies focus on device performance under standard testing conditions and concentrated illumination. The results are compared to a reference lattice mismatched 3J composed of GaInP (1.9 eV)/Ga(In)As (1.4 eV)/GaInAs (1 eV) and to a lattice matched 3J composed of GaInP (1.9 eV)/Ga(In)As (1.4 eV)/Ge (0.67 eV). The advantage of CuInSe2 is its higher absorption coefficient, which requires only 1 μm of active material compared to 4 μm of GaInAs in the bottom subcell of the reference lattice mismatched cell. The proposed design reaches an efficiency of 32.6% under 1 sun illumination at 300 K with 105 cm−2 threading dislocations and 39.6% at 750 suns