Size-Dependent Quantum Confined Stark Effect in Quantum Dot Light-Emitting Diodes: An Electrically Excited Transient Absorption Study

The electric field-induced quantum confined Stark effect is an important factor that can affect the performance of quantum dot light-emitting diodes. However, probing this Stark effect in the operating quantum dot light-emitting diodes is still experimentally challenging using available characterization techniques. Herein we combine our self-developed electrically excited transient absorption spectroscopy with theoretical simulation to unveil the complex size dependence of the Stark effect in quantum dot light-emitting diodes. We found that the Stark effect-induced exciton quenching depends on both wave function confinement and the screening effect. Under reversed biases, the Stark-voltage relationship reveals that smaller quantum dots are less electric field-sensitive because of stronger wave function confinement; while under forward biases, larger quantum dots exhibit stronger electric-field screening and smaller equivalent bias because of more efficient carrier injection─with these intertwined factors, we observed the strongest electric field-induced exciton quenching in medium-size quantum dots.