Regulation of charge distribution for highly efficient colloidal quantum‐well light‐emitting diodes with deep‐red emissions

Two‐dimensional (2D) nanocrystals have recently risen to be highly promising for optoelectronics and microelectronics. However, it is a big challenge for 2D nanocrystals in the applications of long‐wavelength regions (e.g., ≥660 nm) and the development of 2D nanocrystal light‐emitting diodes (LEDs) with long‐wavelength emissions is in its infancy. Here, colloidal quantum‐well LEDs (CQW‐LEDs) with long‐wavelength emissions (671 nm) have been developed, simultaneously achieving high efficiency, extremely low efficiency roll‐off, high luminance, ultra‐saturated emission with CIE coordinates of (0.719, 0.280), and excellent color stability. The photoluminescence quantum yield of designed CdSe/CdZnS core/shell CQW films is as high as 92%. The resultant CQW‐LEDs exhibit an external quantum efficiency (EQE) of 17.45% and a luminance of 9335 cd m −2 , which are record values for 2D nanocrystal LEDs with long‐wavelength emissions. Experiments and simulations reveal that the high performance is attributed to the great enhancement of charge balance, which is fulfilled by the employment of effective triple hole transport layers. The strategy also enables red CQW‐LEDs to achieve an EQE of 20.41%. Such results provide a new approach to obtain CQW‐LEDs, pave the way to realize superior performance 2D nanocrystal LEDs with long‐wavelength emissions, and give a deep insight to regulate charge distribution for nanocrystal LEDs.