Quantum Dot Light Emitting Diodes based on Anisotropic Colloidal Heterostructures
ONE Lab: Giovanni Azzellino, Vladimir Bulović
Collaborators: Igor Coropceanu, Moungi G. Bawendi
Since their inception, electrically driven colloidal quantum-dot light-emitting devices (QD-LEDs) have increased in external quantum efficiency from less than 0.01% to around 20%. The high luminescence efficiency and uniquely size-tunable colour of solution-processable semiconducting colloidal QDs highlight the potential of QD-LEDs for use in energy-efficient, high-colour-quality thin-film display and solid-state lighting applications. The major advantage of such nanostructures is their tunability in terms of size and composition, which allow for a systematic variation of their emission energy. Also, the adoption of a proper architecture has been shown to produce high-efficiency quantum dot LEDs, approaching their theoretical limit, by sandwiching a thin layer of emissive core-shell dots between electron- and hole-transport layers.
Furthermore, additional emergent properties can be attained by changing the shape of these nanostructured materials, such as by transitioning from spherical quantum dots to elongated structures called nanorods (NRs). A key feature that distinguishes nanorods from quantum dots is that the former emit light with a high degree of linear polarization oriented along their long axis. By orienting nanorods parallel to the substrate, the preferential emission of light perpendicular to the plane of the substrate will automatically reduce outcoupling losses, thus allowing higher external quantum efficiencies than can be achieved with QDs in conventional devices. Moreover, by aligning the nanorods in a particular direction, a simple scheme for the fabrication of polarized LEDs can be developed.
TEM of self-aligned CdSe-CdS nanorods drop casted on glass