Current enhancement in direct-doped InAs/GaNAs strain-compensated quantum dot solar cell

We investigated the effect of direct Si-doping of self-organized quantum dots (QDs) in molecular beam epitaxy (MBE) on the performance of QD solar cells (QDSCs). In order to control the quasi-Fermi level of intermediate band (IB) region, 25 stacked layers of InAs/GaNAs QDs were directly doped to n-type with Si during the self-assembling stage of growth. The amount of doping of each InAs QD layer was changed from 5 × 10¹⁰ cm^-2 (one electron per QD) to 25 × 10¹⁰ cm^-2 (five electrons per QD). Improved quantum efficiencies (QE) and photovoltaic properties were achieved for QDSC with doping density of 5 × 10¹⁰ cm^-2 under an irradiation of AM1.5 solar spectrum. Increasing the doping density above the optimum resulted in a degradation of QE and PV properties. In QDSC with a doping density of 5×10¹⁰ cm^-2, or one electron per QD, a photocurrent production due to two-step photon absorption was measured at room temperature detected under filtered air-mass 1.5 solar spectrum.