Improvement of PV Performance by Using Multi-Stacked High Density InAs Quantum Dot Molecules

InAs quantum dot molecules (QDMs) are prepared by thin-capping-and-regrowth MBE process. The dot density can be varied between 10
¹⁰
cm
^-2
, for as-grown quantum dots (QDs), to 10
¹²
cm
^-2
, for multi-stack QDMs. Photocurrent measurements on 1-and 5-stack high-density QDM layers show that these InAs QDMs when embedded inside a GaAs bulk structure extend photon absorption beyond the 850-nm bandedge limited by GaAs. The results also indicate that the higher the number of stacks the higher the resulting current. The presence of high-density QDMs in solar cells thus extends the absorption region and at the same time increase the output current. Electrical characterisations on homojunction (p-n) solar cells with 1-and 5-stack high-density QDMs embedded between the junction show that the 5-stack sample provides a higher short-circuit current density of J
_sc
=14.4 mA/cm
²
compared to 9.6 mA/cm
²
provided by the 1-stack sample. The increase is due entirely to the difference in absorptive dot volume accounted for by the difference in the number of stacks of high-density InAs QDMs. The efficiency of homo-structure 5-stack high-density QDM solar cell is 5.1%