GaAsP/SiGe tandem solar cells on porous Si substrates

III-V compound semiconductors and SiGe alloys can be combined to develop multijunction solar cells on Silicon substrates with optimum bandgap combinations. Current implementations of such devices have reached efficiencies over 20%, using thick –and thus costly– buffer layers which induce the appearance cracks in large area samples. As a strategy mitigate these two issues (thick buffers cracking), GaAsP/SiGe tandem cell has been developed employing group IV reverse graded grown Ge/Si virtual subsurface porous layer. Reverse facilitate reduction threading dislocation density limited thicknesses but also cracks. To minimise this, silicon layer incorporated close interface so that ductility this suppresses crack propagation. In terms performance, reduces problem cracks, not totally supressing them though. Accordingly, low shunt resistance observed previous designs increased improving efficiency, is still notably behind thicker forward layers. The first results new architecture are presented here.