Voltage preservation in Intermediate Band Solar Cells

TL;DR

This paper introduces an analytical optimization method for Intermediate Band Solar Cells, showing that voltage preservation and current matching cannot be achieved simultaneously without an energy shift, which enables both to be satisfied.

Contribution

It proposes a novel optimization approach and demonstrates that an electronic ratchet can simultaneously achieve voltage preservation and current matching in IBSCs.

Findings

Energy shift (electronic ratchet) enables simultaneous voltage preservation and current matching.

Systems with ratchet maintain open-circuit voltage and fill factor similar to single junctions.

Numerical results show ratchet improves short-circuit current without voltage loss.

Abstract

Intermediate Band Solar Cell is an advanced concept for solar energy conversion in which two low-energy photons can promote an electron to the conduction band through a so-called intermediate band. To limit recombination and preserve the photo-generated voltage, generation to- and from the intermediate band should be matched. However, all practical realizations experienced a significant voltage degradation as compared to a single junction without intermediate band. In this work, we develop a novel analytical optimization method based on Lagrange multipliers. We demonstrate that an Intermediate Band Solar Cell under solar spectrum cannot meet voltage preservation and current matching at the same time. By contrast, we show that the implementation of an energy shift (\emph{electronic ratchet}) in any of the bands allows those two criteria to be filled simultaneously. Additional insights are provided by the numerical study of the short circuit current and fill factor of the systems at stake, which show that a system with ratchet benefits from the same current increase as a standard Intermediate Band Solar Cell (same short-circuit current), while maintaining I-V properties of a single junction (same open-voltage circuit, same fill factor).