Abstract
A numerical study is presented of the sub-bandgap interband photon absorption in quantum dot intermediate band solar cells. Absorption coefficients and photocurrent densities are calculated for the valence band to intermediate band transitions using a four-band k·p method. It is found that reducing the quantum dot width in the plane perpendicular to the growth direction increases the photocurrent from the valence band to the intermediate-band ground state if the fractional surface coverage of quantum dots is conserved. This provides a path to increase the sub-bandgap photocurrent in intermediate band solar cells.
Highlights
The intermediate band solar cell (IBSC) is a high efficiency solar cell concept whose detailed balance efficiency limit has been calculated as 63%,1 to be compared to the Schockly-Queisser limit of 41%2 for conventional single-bandgap solar cells
The concept is based on the introduction of an intermediate band (IB) between the valence band (VB) and conduction band (CB) of a semiconductor
The IB allows an increase in photocurrent via a two sub-bandgap photon absorption process in which one photon promotes an electron from the VB to the IB and another promotes an electron from the IB to the CB, creating a single electron-hole pair
Summary
The intermediate band solar cell (IBSC) is a high efficiency solar cell concept whose detailed balance efficiency limit has been calculated as 63%,1 to be compared to the Schockly-Queisser limit of 41%2 for conventional single-bandgap solar cells (both values have been calculated assuming maximum light concentration and treating the sun as a blackbody at 6000 K). IBSCs have been realized in which the IB is constituted by the ground state energy levels of InAs quantum dots (QDs) in a GaAs matrix.. IBSCs have been realized in which the IB is constituted by the ground state energy levels of InAs quantum dots (QDs) in a GaAs matrix.3–8 The bandgaps of this system are not optimal, but it has allowed the basic principles of IB operation to be proven.. The bandgaps of this system are not optimal, but it has allowed the basic principles of IB operation to be proven.9,10 These devices suffer from weak sub-bandgap absorption. IBSCs have been realized in which the IB is constituted by the ground state energy levels of InAs quantum dots (QDs) in a GaAs matrix. The bandgaps of this system are not optimal, but it has allowed the basic principles of IB operation to be proven. These devices suffer from weak sub-bandgap absorption.
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