Hot electron lifetime exceeds 300 nanoseconds in quantum dots with high quantum efficiency

TL;DR

This study demonstrates that hot electrons in quantum dots can have lifetimes exceeding 300 nanoseconds under electrical excitation, significantly longer than previously observed in photoexcited states, due to a phonon bottleneck effect.

Contribution

The paper introduces a new electrically excited transient absorption spectroscopy method revealing long-lived hot electrons in quantum dots, challenging prior assumptions about their rapid cooling.

Findings

Hot electron lifetimes reach up to 371 ns in quantum dot LEDs.

Electrical excitation reveals hot electrons longer-lived than in photoexcitation.

Strong phonon bottleneck effect observed, prolonging hot electron lifetime.

Abstract

Hot electrons are theoretically predicted to be long-lived in strongly confined quantum dots, which could play vital roles in quantum dot-based optoelectronics; however, existing photoexcitation transient spectroscopy investigations reveal that their lifetime is less than 1 ps in well-passivated quantum dots because of the ultrafast electron-hole Auger-assisted cooling. Therefore, they are generally considered absent in quantum dot optoelectronic devices. Here, by using our newly developed electrically excited transient absorption spectroscopy, we surprisingly observed abundant hot electrons in both II-VI and III-VI compound quantum dot light-emitting diodes at elevated bias (>4 V), of which the lifetimes reach 59 to 371 ns, lengthened by more than 5 orders of magnitude compared with the photoexcited hot electrons. These results experimentally prove the presence of a strong phonon bottleneck effect, refreshing our understanding of the role of hot electrons in quantum dot optoelectronics.