Ga-rich Ga_xIn_(1-x)P solar cells on Si with 1.95 eV bandgap for ideal Ⅲ-Ⅴ/Si photovoltaics

摘要

Theoretical models for Ⅲ-Ⅴ compound multijunction solar cells show that solar cells with bandgaps of 1.95-2.3 eV are needed to create ideal optical partitioning of the solar spectrum for device architectures containing three, four and more junctions. For Ⅲ-Ⅴ solar cells integrated with an active Si sub-cell, GaInP alloys in the Ga-rich regime are ideal since direct bandgaps of up to ～ 2.25 eV are achieved at lattice constants that can be integrated with appropriate GaAsP, SiGe and Si materials, with efficiencies of almost 50% being predicted using practical solar cell models under concentrated sunlight. Here we report on Ga-rich, lattice-mismatched Ga_(1057)In_(0.43)P sub-cell prototypes with a bandgap of 1.95 eV grown on tensile step-graded metamorphic GaAs_yP_(1-y) buffers on GaAs substrates. The goal is to create a high bandgap top cell for integration with Si-based Ⅲ-Ⅴ/Si triple-junction devices. Excellent carrier collection efficiency was measured via internal quantum efficiency measurements and with their design being targeted for multijunction implementation (i.e. they are too thin for single junction cells), initial cell results are encouraging. The first generation of identical 1.95 eV cells on Si were fabricated as well, with efficiencies for these large bandgap, thin single junction cells ranging from 7% on Si to 11% on GaAs without antireflection coatings, systematically tracking the change in defect density as a function of growth substrate.