Quantum Dot Intermediate Band Solar Cells: Design Criteria and Optimal Materials

The main limitation of the conventional solar conversion device is that low energy photons cannot. excite charge carriers to the conduction band, therefore do not contribute to the devices's current, and high energy photons are not efficiently used due to a poor match of the solar spectrum to the energy gap. However, if intermediate levels are introduced into the energy gap of a conventional device, then low energy photons can be used to promote charge carriers in a stepwise mariner to the conduction band thereby enhancing the current while maintaining a large open-circuit voltage. This concept is called the intermediate band solar cell and increases the efficiency beyond the thermodynamic limits of the conventional device. A device based on the confined electron levels of quantum dots called the quantum dot intermediate band solar cell is a physical realization of the intermediate band solar cell. In this work, we propose design criteria and optimal material systems that are considered candidates for the quantum dot intermediate band solar cell.;To search for optimal materials. the finite element method is developed and MATLAB code is designed in the context of quantum and continuum mechanics with the sophistication necessary to allow for three dimensional numerical simulations that incorporate realistic assumptions about the quantum dot. The materials considered in this work are the technologically important III-V compound semiconductors and their alloys. Numerical simulations are carried out on quantum dot geometries that have been experimentally observed during self-assembled growth, the technology proposed to achieve the quantum dot intermediate band solar cell, and those material systems that have properties that match those of the intermediate band solar cell with efficiency greater than 46% for unconcentrated light and greater than 62% for fully concentrated light are identified as optimal materials for the quantum dot intermediate band solar cell.