<p> Colloidal quantum
wells (CQWs) are regarded as a new, highly promising class of
optoelectronic materials thanks to their unique excitonic characteristics of high
extinction coefficient and ultranarrow emission bandwidth. Although the exploration
of CQWs in light-emitting diodes (LEDs) is impressive, the performance of
CQW-LEDs lags far behind compared with other types of LEDs (e.g., organic LEDs,
colloidal quantum-dot LEDs, and perovskite LEDs). Herein, for the first time, the authors show high-efficiency CQW-LEDs reaching
close to the theoretical limit. A key factor for this high performance is the
exploitation of hot-injection shell (HIS) growth of CQWs, which enables a near-unity photoluminescence
quantum
yield (PLQY), reduces nonradiative channels, ensures smooth films and enhances
the stability. Remarkably, the PLQY remains 95% in solution and 87% in film despite
rigorous cleaning. Through
systematically understanding their shape-, composition- and device- engineering, the CQW-LEDs using CdSe/Cd<sub>0.25</sub>Zn<sub>0.75</sub>S
core/HIS CQWs exhibit a maximum external quantum efficiency of 19.2%. Additionally, a high luminance of 23,490 cd m<sup>-2</sup>, extremely saturated red color with the Commission
Internationale de L’Eclairage coordinates of (0.715, 0.283) and stable emission
are obtained. The findings indicate that HIS grown CQWs enable high-performance
solution-processed LEDs, which may pave the path for CQW-based display and
lighting technologies.</p>
High-efficiency BAlGaN/AlN quantum well structures for optoelectronic applications in ultraviolet spectral region