Material Selection for the Quantum Dot Intermediate Band Solar Cell

Abstract

The main limitation of the conventional solar conversion device is that low energy photons cannot excite charge carriers to the conduction band and therefore do not contribute to the device’s current. Another limitation is that high energy photons are not efficiently used due to a poor match of the solar spectrum to the energy gap. However, when intermediate bands are introduced into the energy gap of a conventional device, low energy photons can be used to promote charge carriers in a stepwise manner to the conduction band and photons are better matched to the energy transitions between bands. Solar cells with intermediate bands can have conversion efficiencies that exceed thermodynamic limits of the conventional solar cells. 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. We discuss the design criteria for selecting materials for the quantum dot intermediate band solar cells. With the aid of the finite element method, we perform numerical simulations on two types of quantum dot geometry and identify optimal material systems that are considered candidates for the quantum dot intermediate band solar cell with efficiencies greater than 46 % for unconcentrated light and greater than 62 % for fully concentrated light. Materials considered in this work are the technologically important III–V semiconductors and their alloys.