Photoluminescent quantum-dot light emitting devices controlled by electric field induced quenching

Abstract

Colloidal quantum dots (QDs) have been promising luminophores due to their bright, pure, and tunable colors. The ability to control the emission properties of QDs has far-reaching potential applications for a new generation of display and lighting technologies. The emission control of QDs in a QD light-emitting device (LED) is usually achieved by changing the injection current density. However, these devices face issues with lifetime and stability as well as low external quantum efficiency (EQE) at high biases. In this thesis, we demonstrate a unique approach in operating a QD device that avoids these limitations. The device is a photoluminescent LED (PL-LED) where the emission from the LED is from optical excitation. To tune the emission, we apply a bias to intentionally dim or turn off the QD PL, using the PL quenching at high biases to our advantage. We also study the field-induced quenching mechanisms using capacitor structured PL-LEDs and QD-LEDs. Traditional electroluminescent QD-LEDs can be used as a PL-LED when operated under reverse bias. We propose that the electric-field induced quenching in our devices is due to exciton dissociation and reduced band-edge exciton formation at high field strengths. The resulting QD PL device exhibits voltage-controlled PL quenching up to 99.5%, corresponding to a high contrast ratio of 200:1, and a sub-microsecond response time. Our demonstration of PL tunability can lead to a new class of devices for fluorescent displays and voltage-controlled devices.