Characterisation of quantum dot-intermediate band solar cells with optical spectroscopy
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- Institutt for fysikk 
This report describes the development of a photoreflectance (PR) technique in order to study InAs/GaAs quantum dots-based intermediate band solar cells (QD-IBSC). The motivation for this study, is that PR has previously been applied to detect the optical transitions involving the intermediate band as well as the excited states of the quantum dots (QDs). Such excited states are detrimental for the QD-IBSC performance, and they are not readily detected by photoluminescence (PL).The PR signals show several unique peaks for all samples, related to their properties. The Franz-Keldysh oscillations (FKO) are observed and the fitting is done by using Airy function. These oscillations can be used to determine electro-optic energy and the built-in electric field. Energy bandgap of the various materials composing the sample (Al(0.3)Ga(0.7)As, GaAs, wetting layer (WL) and QDs) is resolved using first derivative Lorentzian lineshape function. To complement PR findings, PL measurements for a wide range of excitation energies are conducted at room-temperature. The energy bandgap of the WL is identified in the low PL excitation energy.