Inverted growth evaluation for epitaxial lift off (ELO) quantum dot solar cell and enhanced absorption by back surface texturing

Thin ELO devices with light management allow for increased quantum dot (QD) absorption without the need for excessive strain management. A growth study was designed to evaluate challenges regarding inverted growth of ELO QDSCs. Two upright GaAs cell designs were investigated: a standard device and a “thick emitter” device. For each design, two QDSCs and a baseline without QDs were grown and fabricated. One standard QDSC was annealed for two hours while one thick emitter QDSC had an increased QD superlattice period. The standard baseline had a Jsc of 20.7 mA/cm
²
and a Voc of 1.01 V, while the standard QDSC had a J
_SC
of 21.2 mA/cm
²
and V
_oc
of 0.988 V. The thick emitter baseline had a J
_SC
of 21.4 mA/cm
²
and a V
_oc
of 1.04, while the thick emitter QDSC with increased period had a J
_SC
of 21.9 mA/cm
²
and V
_oc
of 0.99 V which is on par with the best reported QDSC Voc
^s
· Finally, inverted GaAs cells with and without QDs were fabricated with back surface reflectors (BSRs) and removed from the substrate by ELO. Devices with flat BSRs and textured BSRs are compared. The QDSC with the flat BSR had a sub-bandgap integrated spectral response equivalent to 0.38 mA/cm
²
while the textured BSR showed 0.57 mA/cm
²
, which represents a 30% increase over the flat BSR.