“Professor Demir’s research team demonstrate record-high external quantum efficiency of 19.2% achieved in light-emitting diodes of colloidal quantum wells enabled by hot-injection shell growth”. Colloidal quantum wells (CQWs) have recently emerged as a new family of semiconductor nanocrystals with distinctive structural and electronic properties originating from their atomically flat structure. Thanks to the tight quantum confinement only in the vertical direction, CQWs possess many unique thickness-dependent optical characteristics and are highly attractive for light-emitting diodes (LEDs). However, despite the exploration of CQWs is impressive, the performance of CQW-LEDs lags far behind when compared with other types of LEDs showing the benchmark external quantum efficiency (EQE) of ~20%, such as organic LEDs (OLEDs), colloidal quantum-dot LEDs (CQD-LEDs), and perovskite LEDs (PeLEDs). In fact, it is a challenge for CQW-LEDs to simultaneously achieve high efficiency and high luminance, especially for red CQW-LEDs due to the low luminance perception of human eyes. This has been attributed to the use of inefficient CQW emitters, poor film morphology, and uncontrolled charge injection and balance. Thus, in spite of the excellent optical features from CQW emitters in solution form, the demonstration of highly efficient, stable and saturated CQW-based LEDs was missing.
In a recent communication published in Advanced Materials, a team of researchers led by Professor Demir has successfully demonstrated the first account of CQW-LED with the EQE comparable to state-of-the-art OLEDs, CQD-LEDs, and PeLEDs. According to Prof. Demir, the core/hot-injection shell (HIS) CQWs in principle can overcome the aforementioned limitations in the LEDs with near-unity photoluminescence quantum yield (PLQY), reduced nonradiative emission, smooth film, and improved stability. Through an understanding of the shape-, composition- and device- engineering, the CQW-LEDs based on CdSe/Cd0.25Zn0.75S core/HIS CQWs can exhibit an EQE of 19.23%, which is close to the theoretical maximum of 20%. Additionally, a high luminance of 23,490 cd m-2, an extremely saturated red color with the Commission Internationale de L’Eclairage (CIE) coordinates of (0.715, 0.283) along with highly stable emission at different luminance levels is achieved. Prof. Demir emphasized that the present work is promising to be extended to various-color CQW-LEDs and imply that HIS-grown CQWs enable high-performance solution-processed LEDs, which may pave the path for commercial CQW-based display and lighting technologies.
Further details can be found in the latest communication in Advanced Materials (DOI: 10.1002/adma.201905824, https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201905824). This record performance is also highlighted on the cover.
(Artwork: Mete Duman, UNAM)