Coherent Phonons-Driven Hot Carrier Effect in a Superlattice Solar Cell

TL;DR

This paper theoretically demonstrates that coherent phonons can reduce carrier thermalization in superlattice solar cells, enhancing hot carrier effects and potentially improving solar cell efficiency by leveraging quantum coherence properties.

Contribution

It introduces a model showing how phonon coherence weakens electron-phonon coupling, leading to reduced thermalization power and improved hot carrier effects in superlattice solar cells.

Findings

Coherent LO phonons weaken electron-phonon coupling.

Thermalization power is significantly reduced by phonon coherence.

Experimental evidence supports the coherent phonon-driven phenomenon.

Abstract

Carrier thermalization in a superlattice solar cell made of polar semiconductors is studied theoretically by considering a minimal model where electron-phonon scattering is the principal channel of carrier energy loss. Importantly, the effect of an intrinsic quantum mechanical property; the phonon coherence, on carrier thermalization is investigated, within semiclassical picture in terms of phonon wave packet. It turns out that coherent longitudinal optical (LO) phonons weaken the effective electron-phonon coupling, thus supposedly lowering the carrier energy loss rate in solar cell. The resulting thermalization power is indeed significantly reduced by the coherent phonons, resulting in enhanced hot carrier effect, particularly for thin enough well layer where carrier confinement is also strong. A recent experiment on superlattice solar cell prototype is shown to manifest the coherent phonons-driven phenomenon. Our results demonstrate the practical implications of the fundamental quantum coherence property of phonons in semiconductors for improving superlattice solar cell performance, via hot carrier effect.