Electroluminescence From Colloidal Nanocrystals (Quantum Dots) Via Field-Driven Ionization

Colloidal semiconductor nanocrystals, or quantum dots (QDs), are a promising class of materials for the development of next-generation solid-state lighting technologies due to their facile solution-based syntheses, widely tunable and narrowband emission characteristics, and high photoluminescence efficiencies. However, obtaining efficient and sustained electroluminescence from QD thin films remains a significant challenge. A high degree of morphological and energetic disorder inherent to many nanosized lumophores, including QDs, places severe limitations on the charge injection into and transport rates through thin films of these materials. Here, we demonstrate that sustained electroluminescence from QD thin films can be achieved by the local generation and recombination of charges induced by the application of an alternating electric field, thereby eliminating the need for injection of charge carriers from the device electrodes and long-range carrier transport. We show electroluminescence from novel light-emitting structures containing thin films of QDs and other nanoscale emissive materials that do not support direct current excitation, and suggest a mechanism for the charge generation and electroluminescence that is consistent with our time-averaged and time-resolved experimental observations. The proposed field-driven ionization phenomenon may provide a new route toward the realization of efficient lighting and display platforms incorporating colloidal QDs.