Nonradiative lifetimes in intermediate band materials - absence of lifetime recovery

TL;DR

This paper demonstrates that lifetime recovery in intermediate band materials via the insulator-to-metal transition is not feasible because phonon-induced localization prevents extended states from enhancing carrier lifetime, guiding future research directions.

Contribution

It shows that lifetime recovery through the insulator-to-metal transition does not occur in intermediate band materials due to phonon localization effects.

Findings

Lifetime recovery via insulator-to-metal transition is impossible.

Metallic extended states become localized by phonons during recombination.

Only trivial lifetime improvements are achievable through level shifts.

Abstract

Intermediate band photovoltaics hold the promise of being highly efficient and cost effective photovoltaic cells. Intermediate states in the band gap, however, are known to facilitate nonradiative recombination. Much effort has been dedicated to producing metallic intermediate bands in hopes of producing lifetime recovery -- an increase in carrier lifetime as doping levels increase. We show that lifetime recovery induced by the insulator-to-metal transition will not occur, because the metallic extended states will be localised by phonons during the recombination process. Only trivial forms of lifetime recovery, e.g., from an overall shift in intermediate levels, are possible. Future work in intermediate band photovoltaics must focus on optimizing subgap optical absorption and minimizing recombination, but not via lifetime recovery.