High-efficiency blue and white electroluminescent devices based on non-Cd I−III−VI quantum dots

Abstract

Research direction of colloidal quantum dot (QD)-based LEDs (QLEDs), whose performance has substantially progressed over last two decades, has been oriented mostly to the fabrication of next-generation, high-color gamut display devices particularly based on Cd-containing QDs, while their extension to solid-state planar lighting application remains nearly unexplored. In this work, we report on all-solution-processed fabrication of group I–III–VI chalcogenide, non-Cd QDs-based high-efficiency white lighting electroluminescent (EL) devices. For this, using Zn–Cu–Ga–S (ZCGS) QD emitters having a high photoluminescence quantum yield (PL QY) of 80% a multilayered blue QLED consisting of poly(9-vinylcarbazole) hole transport layer (HTL) and Mg-alloyed ZnO nanoparticle electron transport layer (ETL) is first fabricated, showing a maximum external quantum efficiency (EQE) of 7.1%. Then, white QLEDs containing a mixture of blue ZCGS and yellow Cu–In–S QDs as a single emitting layer (EML) are constructed with the same HTL/ETL combination as above. White EL spectral distribution is facilely tunable simply by varying ZCGS-to-CIS QD content ratio in the EML of white EL device. The optimum white QLED not only generates the peak quantities of 2172 cd/m2 in luminance and 4.6% in EQE, corresponding to the record values ever reported in non-Cd white EL devices, but exhibits high color rendering index up to 82.