High-Performance Deep Red Colloidal Quantum Well Light-Emitting Diodes Enabled by the Understanding of Charge Dynamics

Colloidal quantum wells (CQWs) have emerged as a promising family of two-dimensional (2D) optoelectronic materials with outstanding properties, including ultranarrow luminescence emission, nearly unity quantum yield, and large extinction coefficient. However, the performance of CQWs-based light-emitting diodes (CQW-LEDs) is far from satisfactory, particularly for deep red emissions (≥660 nm). Herein, high efficiency, ultra-low-efficiency roll-off, high luminance, and extremely saturated deep red CQW-LEDs are reported. A key feature for the high performance is the understanding of charge dynamics achieved by introducing an efficient electron transport layer, ZnMgO, which enables balanced charge injection, reduced nonradiative channels, and smooth films. The CQW-LEDs based on (CdSe/CdS)@(CdS/CdZnS) ((core/crown)@(colloidal atomic layer deposition shell/hot injection shell)) show an external quantum efficiency of 9.89%, which is a record value for 2D nanocrystal LEDs with deep red emissions. The device also exhibits an ultra-low-efficiency roll-off and a high luminance of 3853 cd m-2. Additionally, an exceptional color purity with the CIE coordinates of (0.719, 0.278) is obtained, indicating that the color gamut covers 102% of the International Telecommunication Union Recommendation BT 2020 (Rec. 2020) standard in the CIE 1931 color space, which is the best for CQW-LEDs. Furthermore, an active-matrix CQW-LED pixel circuit is demonstrated. The findings imply that the understanding of charge dynamics not only enables high-performance CQW-LEDs and can be further applied to other kinds of nanocrystal LEDs but also is beneficial to the development of CQW-LEDs-based display technology and related integrated optoelectronics. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) This work was supported in part by National Natural Science Foundation of China under grant nos. 62104265 and 61922090, in part by the Science and Technology Program of Guangdong Province under grant no. 2021A0505110009, and in part by the Innovation and Technology Fund under Grant GHP/006/20GD. J. C. Huang thank the CityU fund (no. 9380088). Y.M. acknowledges the support from the National Natural Science Foundation of China (no. U20A20340), National Key Research and Development Program of China (no. 2020YFB0408100) and Guangdong Innovative and Entrepreneurial Research Team Program (no. 2016ZT06C412). Q.X. acknowledges support from Guang-dong Basic and Applied Basic Research Foundation for Distinguished Young Scholar (no. 2021B1515020028) and the Science and Technology Program of Guangzhou, China (no. 201904010147). H.V.D. gratefully acknowledges financial support in part from Agency for Science, Technology and Research (A*STAR) MTC program, grant no. M21J9b0085 (Singapore), Ministry of Education Tier 1 grant MOE-RG62/ 20 (Singapore) and TUBITAK 115F297, 117E713, 119N343, 121N395, and 20AG001, and support from TUBA.