Numerical simulation of QD-intermediate band solar cells: effect of dot size on performance

In this work, we present a Quantum Dot Intermediate Band Solar Cell (QD-IBSC) photogeneration model that is based on detailed balance principles. The 3D Schrodinger equation is solved for a regimented array of cubic quantum dots known as a Quantum Dot Crystal (QDC). Energy levels used in the simulation are derived from the dispersion relation. We consider only the dispersion relation along the [100] quasi-crystallographic direction. Absorption coefficients used were assumed to be constant and non-overlapping for each energy transition. Various JV curves were simulated for different dot sizes for the InAs0.9N0.1/GaAs0.98Sb0.02 dot/host system. This material system was chosen due to its property of a negligible valance band offset. The negligible valance band offset offers more feasibility for the isolation of the intermediate band. Simulations were done under a non-concentrated 6000K black body spectrum at a cell temperature of 300K. Performance parameters for each IV curve were calculated in order to ascertain the effect of dot size on performance from a fundamental level. Results show that for a fixed dot separation of 2nm, cell efficiency increases to 36.7% as the dot size is increased to 3.5 nm, but begins to decrease for larger dot sizes.