Optoelectronic excitations and photovoltaic effect in strongly correlated materials

TL;DR

This study reveals that strongly correlated insulators like vanadium dioxide exhibit rapid impact ionization, potentially enabling more efficient solar energy conversion by surpassing the limitations of conventional semiconductor-based solar cells.

Contribution

It demonstrates, through ab initio calculations, that strong Coulomb interactions in strongly correlated insulators lead to high impact ionization rates, opening new avenues for photovoltaic materials.

Findings

Impact ionization rate in vanadium dioxide is two orders of magnitude higher than in silicon.

Strong Coulomb interactions cause rapid decay of photo-excited electron-hole pairs.

Potential for broader class of materials to be used in efficient solar energy conversion.

Abstract

Solar cells based on conventional semiconductors have low efficiency in converting solar energy into electricity because the excess energy beyond the gap of an incident solar photon is converted into heat by phonons. Here we show by ab initio methods that the presence of strong Coulomb interactions in strongly correlated insulators (SCI) causes the highly photo-excited electron-hole pair to decay fast into multiple electron-hole pairs via impact ionization (II). We show that the II rate in the insulating $M_1$ phase of vanadium dioxide (chosen for this study as it is considered a prototypical SCI) is two orders of magnitude higher than in Si and much higher than the rate of hot electron/hole decay due to phonons. Our results indicate that a rather broad class of materials may be harnessed for an efficient solar-to-electrical energy conversion that has been not considered before.