Abstract
This study demonstrates the feasibility of improving the performance of a quantum dot (QD) intermediate band solar cell (SC) by capping an InGaAs layer on the InAs QDs and inserting GaAs spacer layers. For comparison, a GaAs reference SC of the same p-i-n structure but without InAs QDs is grown. The two devices were grown by solid source molecular beam epitaxy (SS-MBE) on epiready (001) n(+)-GaAs substrates and the InAs QDs structure is highly stacked and well-aligned. The two SCs were investigated by sepectroscopic ellipsometry (SE), in the photon energy range of 1-6 eV, photoluminescence (PL) and photo-absorption measurements. The two major spectral features observed in the dielectric function spectra of the InAs QDs SC at similar to 3 eV and similar to 4.5 eV are attributed to the E1 and E2 critical point structures of GaAs and InAs, respectively. The PL spectrum of the InAs QDs in the GaAs matrix is higher and presents an asymmetric shape, which indicated the growth of a high-quality multistacked InAs QDs structure and the contribution of larger and relatively smaller QDs to PL spectrum. The electrical conversion at the infrared range of lambda=850-1300 nm for the InAs QDs SC is demonstrated by photocurrent spectra. The enhanced absorption performance (up to 1280 nm) of the QDs SC was attributed to the optical absorption from InAs QDs, wetting layer and InGaAs layer of the InAs/InGaAs/GaAs QD heterostructure. (C) 2013 Elsevier B.V. All rights reserved.