Demonstration of a GaSb/GaAs Quantum Dot Intermediate Band Solar Cell Operating at Maximum Power Point.

I. Ramiro,J. Villa,A. J. Martin,A. Martí,J. Hwang,J. Phillips,J. Millunchick

doi:10.1103/physrevlett.125.247703

Abstract

Intermediate band solar cells (IBSCs) promise high efficiencies while maintaining a low device structural complexity. A high efficiency can be obtained by harvesting below-band-gap photons, thus increasing the current, while at the same time preserving a high voltage. Here, we provide experimental proof that below-band-gap photons can be used to produce nonzero electrical work in an IBSC without compromising the voltage. For this, we manufacture a GaSb/GaAs quantum-dot IBSC. We use light biasing and make our cell operate at the maximum power point at 9K. We measure the photocurrent response to absorption of photons with an energy of less than 1.15eV while the cell is operating at 1.15V. We also show that this result implies the existence of three quasi-Fermi levels linked to the three electronic bands in our device, as demanded by the IBSC theory to preserve the output voltage of the cell.

Highlights

The conversion efficiency of conventional solar cells is fundamentally limited by the fact that they rely on singlegap (SG) semiconductors as the absorbing material
By delivering a higher current while maintaining a high output voltage, the Intermediate band solar cells (IBSCs) breaks with the trade-off between current and voltage that governs single-gap solar cells (SGSCs) and can, achieve higher efficiencies
Simultaneous demonstration of below-band-gap photocurrent and voltage preservation is key to strengthening the validity of the IBSC framework because, as we shall show, it implies the existence of three distinct quasi-Fermi levels (QFLs), a necessary condition for exceeding the efficiency limit of SGSCs

Summary

Introduction

The conversion efficiency of conventional solar cells is fundamentally limited by the fact that they rely on singlegap (SG) semiconductors as the absorbing material. The band gap of the SG material sets the upper limit for both the generated current and the output voltage of the cell.

Results

Conclusion