Quantum-dot density dependence of power conversion efficiency of intermediate-band solar cells

For intermediate-band solar cells containing GaAs/InAs quantum dots (QDs), the QD density dependence of the power conversion efficiency (PCE) was theoretically calculated for various sun concentrations under AM1.5 conditions based on detailed balance principles. A QD density of over 5 x 10(13) cm(-2) was required to achieve a PCE of more than 50% under 10 000 suns. However, under the photo-filled state and 1 sun, the PCE decreased over a wide total QD density range from about 3 x 10(10) to 1 x 10(13) cm(-2). This reduction was attributed to the negative net carrier generation rate through the intermediate band, which was due to insufficient two-step optical absorption. The short-circuit current density increased as the QD density increased up to about 1 x 10(11) cm(-2) and it then saturated. In contrast, the open-circuit voltage decreased with increasing QD density. This reduction in the open-circuit voltage was suppressed at high sun concentrations. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4771925]