Graded band gap GaInNAs solar cells

Abstract

Dilute nitride GaInN(Sb)As with a band gap (Eg) of 1.0 eV is a promising material for the integration in next generation multijunction solar cells. We have investigated the effect of a compositionally graded GaInNAs absorber layer on the spectral response of a GaInNAs sub cell. We produced band gap gradings (ΔEg) of up to 39 meV across a 1 μm thick GaInNAs layer. Thereby, the external quantum efficiency - compared to reference cells - was increased due to the improved extraction of photo-generated carriers from 34.0% to 36.7% for the wavelength range from 900 nm to 1150 nm. However, this device figure improvement is accompanied by a small decrease in the open circuit voltage of about 20 mV and the shift of the absorption edge to shorter wavelengths.