High-Performance, Solution-Processed, and Insulating-Layer-Free Light-Emitting Diodes Based on Colloidal Quantum Dots (original) (raw)
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Infrared Physics & Technology, 2010
Colloidal quantum dot light-emitting devices (QD-LEDs) have generated considerable interest for applications such as thin film displays with improved color saturation and white lighting with a high color rendering index (CRI). We review the key advantages of using quantum dots (QDs) in display and lighting applications, including their color purity, solution processability, and stability. After highlighting the main developments in QD-LED technology in the past 15 years, we describe the three mechanisms for exciting QDs Á optical excitation, Fö rster energy transfer, and direct charge injection Á that have been leveraged to create QD-LEDs. We outline the challenges facing QD-LED development, such as QD charging and QD luminescence quenching in QD thin films. We describe how optical downconversion schemes have enabled researchers to overcome these challenges and develop commercial lighting products that incorporate QDs to achieve desired color temperature and a high CRI while maintaining efficiencies comparable to inorganic white LEDs (65 lumens per Watt). We conclude by discussing some current directions in QD research that focus on achieving higher efficiency and air-stable QD-LEDs using electrical excitation of the luminescent QDs.
Nano Letters, 2012
We report highly bright and efficient inverted structure quantum dot (QD) based light-emitting diodes (QLEDs) by using solution-processed ZnO nanoparticles as the electron injection/transport layer and by optimizing energy levels with the organic hole transport layer. We have successfully demonstrated highly bright red, green, and blue QLEDs showing maximum luminances up to 23 040, 218 800, and 2250 cd/m 2 , and external quantum efficiencies of 7.3, 5.8, and 1.7%, respectively. It is also noticeable that they showed turn-on voltages as low as the bandgap energy of each QD and long operational lifetime, mainly attributed to the direct exciton recombination within QDs through the inverted device structure. These results signify a remarkable progress in QLEDs and offer a practicable platform for the realization of QD-based full-color displays and lightings.
Nature Nanotechnology, 2018
Colloidal Quantum Dot (CQD) light emitting diodes (LEDs) have delivered compelling performance in the visible, yet infrared CQD LEDs underperform their visible-emitting counterparts, largely due to their low photoluminescence quantum efficiency (PLQE). Herein, we employ a ternary blend of CQD thin film comprising a binary host matrix that serves to electronically passivate as well as to cater for efficient and balanced carrier supply to the emitting QD species. In doing so, we report on infrared PbS CQD LEDs with external quantum efficiency of ~7.9% and power conversion efficiency of ~9.3%, thanks to their very low trap-state density on the order of 10 14 cm-3 and very high PLQE in electrically conductive QD solids of more than 60%. When these blend devices operate as solar cells they deliver VOC approaching their radiative limit thanks to the synergistic effect of reduced trap state density and the density of states modification in the nanocomposite. Near and shortwave infrared (NIR, SWIR) light emitting diodes serve a rather broad range of applications, including night vision 1 , surveillance 2 , remote sensing 3 , biological imaging 4 and spectroscopy 5. Recent progress in on-chip and wearable infrared spectroscopy for quality inspection, health and process monitoring also requires the development of highly efficient,
Highly Efficient, Bright, and Stable Colloidal Quantum Dot Short‐Wave Infrared Light‐Emitting Diodes
Advanced Functional Materials, 2020
Unbalanced charge injection is deleterious for the performance of colloidal quantum dot (CQD) light‐emitting diodes (LEDs) as it deteriorates the quantum efficiency, brightness, and operational lifetime. CQD LEDs emitting in the infrared have previously achieved high quantum efficiencies but only when driven to emit in the low‐radiance regime. At higher radiance levels, required for practical applications, the efficiency decreased dramatically in view of the notorious efficiency droop. Here, a novel methodology is reported to regulate charge supply in multinary bandgap CQD composites that facilitates improved charge balance. The current approach is based on engineering the energetic potential landscape at the supra‐nanocrystalline level that has allowed to report short‐wave infrared PbS CQD LEDs with record‐high external quantum efficiency in excess of 8%, most importantly, at a radiance level of ≈5 W sr−1 m2, an order of magnitude higher than prior reports. Furthermore, the balance...
Colloidal quantum dots for optoelectronics
Journal of Materials Chemistry A, 2017
This review is focused on new concepts and recent progress in the development of three major quantum dot (QD) based optoelectronic devices: photovoltaic cells, photodetectors and LEDs.
Quantum Dot Light-Emitting Devices: Beyond Alignment of Energy Levels
ACS Applied Materials & Interfaces
Multinary semiconductor nanoparticles such as CuInS 2 , AgInS 2 , and the corresponding alloys with ZnS hold promise for designing future quantum dot light-emitting devices (QLED). The QLED architectures require matching of energy levels between the different electron and hole transport layers. In addition to energy level alignment, conductivity and charge transfer interactions within these layers determine the overall efficiency of QLED. By employing CuInS 2 −ZnS QDs we succeeded in fabricating red-emitting QLED using two different hole-transporting materials, polyvinylcarbazole and poly(4butylphenyldiphenylamine). Despite the similarity of the HOMO−LUMO energy levels of these two hole transport materials, the QLED devices exhibit distinctly different voltage dependence. The difference in onset voltage and excited state interactions shows the complexity involved in selecting the hole transport materials for display devices.