Progress in narrow gap InGaAs/InP element for tandem solar cells

Narrow gap In/sub 0.53/Ga/sub 0.47/As/InP solar cells illuminated through a transparent InP substrate are the best candidates for fabrication on their base bottom cells combined with GaAs or InP top cells in mechanically stacked tandem concentrator solar cells. The In/sub 0.53/Ga/sub 0.47/As/InP (hereafter InGaAs) heterostructures were grown by liquid phase epitaxy. They consist of four epitaxial layers: n-InP (buffer); n-InGaAs and p-InGaAs (photoactive); p/sup +/-InGaAs (barrier+contact). This work describes the influence of an InP/InGaAs window/emitter interface region, emitter and base thickness on the collection efficiency of solar cells and the short-circuit current. The thick (1.7-2.0 /spl mu/m) and slightly doped emitter maximizes the photocarrier generation in the emitter and space charge depletion region. Our study shows that collection efficiency values as high as 90% were measured in the spectral range of 1000-1600 nm for developed cells. It allowed us to obtain a photocurrent of 30.6 mA/cm/sup 2/ (AM0, 1 Sun). This result was confirmed in the NASA LeRC.