Influence of GaInP ordering on the electronic quality of concentrator solar cells

Abstract

The ordering phenomenon produces a reduction in the band gap of the GaInP material. Though a drawback for many optoelectronic applications, ordering can be used as an additional degree of material and device engineering freedom. The performance of the record efficiency GaInP/GaAs/Ge multijunction solar cells depends on the quality and design of the GaInP top cell, which can be affected also by ordering. The tradeoff existing between band gap and minority carrier properties, and the possibility of creating a back surface field (BSF) structure based on an order–disorder GaInP heterostructure makes the study of the ordering appealing for solar cell applications. In this work, the ordering dependency with the growth conditions and substrate orientation is studied. The results obtained are presented to enrich and extend the data available in the literature. Then the properties of order–disorder GaInP heterostructures are assessed by using them as BSF in GaInP concentrator solar cells. The external quantum efficiency (EQE) shows a good behavior of these BSF layers, but unexpectedly poor electronic quality in the active layers. Although the exact origin of this problem remains to be known, it is attributed to traps introduced by the ordered/disordered domains matrix or growth native defects. EQE measurements with bias light show a recovery of the minority carrier properties, presumably due to the saturation of the traps.