Very high efficiency triple junction solar cells grown by MOVPE

The GaInP/GaInAs/Ge triple junction (3J) space cell technology is nearing practical achievable conversion efficiency limits of ∼30% under 1-sun AM0 illumination. We present solar cell device-modeling results that indicate the GaInP/GaAs/GaInAs architecture with optimal bandgap energies will produce an additional 4% output power relative to the present GaInP/GaInAs/Ge 3J space cell technology. We have grown the GaInP/GaAs/GaInAs 3J cell on GaAs substrates in an inverted fashion incorporating a 1.0 eV metamorphic GaInAs cell, using metal-organic vapor-phase epitaxy (MOVPE) in a production scale reactor. Nearly strain-free growth of the metamorphic GaInAs cell was verified by high-resolution X-ray reciprocal space mapping. From cathodoluminescence (CL) data, the 1.0 eV metamorphic GaInAs cell threading dislocation density (TDD) is estimated to be 5×10 6 cm −2. With this level of TDDs we are able to produce a 3J IMM cells with a one-sun AM0 efficiency of 32%. In addition, external quantum efficiency (EQE) data suggests that improvements in current matching of the subcells will result in an AM0 efficiency of 33%.