Single-nanowire, low-bandgap hot carrier solar cells with tunable open-circuit voltage

TL;DR

This paper demonstrates a low-bandgap InAs nanowire hot carrier solar cell with tunable open-circuit voltage, surpassing traditional efficiency limits by using heterostructures as energy filters to harvest hot carriers effectively.

Contribution

It introduces a novel low-bandgap hot carrier solar cell design with tunable voltage using heterostructures, advancing the potential for higher efficiency solar energy conversion.

Findings

Achieved open-circuit voltage exceeding Shockley-Queisser limit.

Demonstrated tunability of photovoltage through heterostructure design.

Provided insights into realizing high-voltage hot carrier cells in low-bandgap materials.

Abstract

Compared to traditional pn-junction photovoltaics, hot carrier solar cells offer potentially higher efficiency by extracting work from the kinetic energy of photogenerated "hot carriers" before they cool to the lattice temperature. Hot carrier solar cells have been demonstrated in high-bandgap ferroelectric insulators and GaAs/AlGaAs heterostructures, but so far not in low-bandgap materials, where the potential efficiency gain is highest. Recently, a high open-circuit voltage was demonstrated in an illuminated wurtzite InAs nanowire with a low bandgap of 0.39 eV, and was interpreted in terms of a photothermoelectric effect. Here, we point out that this device is a hot carrier solar cell and discuss its performance in those terms. In the demonstrated devices, InP heterostructures are used as energy filters in order to thermoelectrically harvest the energy of hot electrons photogenerated in InAs absorber segments. The obtained photovoltage depends on the heterostructure design of the energy filter and is therefore tunable. By using a high-resistance, thermionic barrier an open-circuit voltage is obtained that is in excess of the Shockley-Queisser limit. These results provide generalizable insight into how to realize high voltage hot carrier solar cells in low-bandgap materials, and therefore are a step towards the demonstration of higher efficiency hot carrier solar cells.