Study on spectral response of schottky-type multi-stack high density quantum dot molecule photovoltaic cells at concentrated light

Schottky-type multi-stack InAs high density quantum dot molecule (HD-QDM) solar cells are fabricated by a modified MBE techniques and tested for their spectral responses at concentrated light conditions. Extended spectral response beyond the bandedge of GaAs, wavelength longer than 870 nm, is obtained from quantum dot (QD) nanostructures. 3 stack HD-QDMs are compared with 15 stack QDs both in their spectral responses and photoluminescence (PL) peaks. PL measurements are conducted between 20 and 298 K. In contrary to narrow PL peaks showing fine spectrum structure at 20K of QDs, HD-QDMs have strong and broad symmetrical PL spectrum with FWHM of 70meV which reflects high dot density and dot size variation. HD-QDM solar cell is tested at concentrated light of 1-3 suns calibrated by standard Si cell and solar simulator. It is estimated that the spectral response beyond 870 nm, originating from the HD-QDMs, contribute to 35-40% extra converted power.