Defect-mediated carrier loss via radiative recombination in GaxIn1-xP top solar cell subcell for high-efficiency multijunction photovoltaic solar cells

Abstract

In this work, the spatial distribution of carrier loss via radiative recombination is studied as a function of forward bias in the GaxIn1-xP top subcell of a GaxIn1-xP/GaAs double-junction tandem solar cell by using micro-electroluminescence (EL) image surveying. An inhomogeneity feature of the EL emission intensity is observed, in which the intensity is uneven and spatially nonuniform across the different cell regions. This feature shows significant dependence on carrier injection concentration. By evaluating the generation rate of EL emitted photons, the observed emission inhomogeneity is believed to be associated with the localization of minority carriers. The region with higher EL intensity is due to the stronger capturing of injected carriers, while the spatial nonuniformity of EL intensity is explained by the uneven distribution of trapping centers and the carrier filling effect of the trapping sites with increased injection levels. The localized trapping centers are possibly be incorporated by the intrinsic/structural defects, impurities diffusion, or the complexes of both. On the basis of these findings, the significance of defect and impurity engineering in GaInP top subcell is advised for achieving better energy conversion efficiency in the GaxIn1-xP -based multijunction photovoltaic devices.