CdS/CdSe/CdS Spherical Quantum Wells with Near-Unity Biexciton Quantum Yield for Light-Emitting-Device Applications

Compared to zero-dimensional (0D) semiconductor quantum dots, 2D semiconductor nanoplatelets (NPLs) offer a spectrally narrow luminescence and superior absorption coefficients, which makes this geometry an attractive candidate for optoelectronic applications. However, optical devices based on NPLs still suffer from nonradiative Auger decay of multiple excitons (MX), which limits the efficiency of the processes, including MX luminescence, electroluminescence, and optical gain. Here, we demonstrate that Auger recombination is strongly suppressed in spherically shaped nanoplatelets, called quantum shells (QSs), where a relaxed confinement of charges leads to diminished exciton–exciton interactions. In particular, we use single photon counting and photon correlation spectroscopy to show that two-dimensional CdS/CdSe/CdS core/shell/shell spherical QSs reach near-unity biexciton emission yield. The Auger suppression was found most prominent in QSs with the largest shell diameter. A combination of ultralong (>15 ns) biexciton (BX) emission lifetimes and strong exciton–exciton repulsion in these QS samples allowed demonstrating low-threshold amplified spontaneous emission (ASE), large modal gain, and microcavity lasing featuring sharp emission modes at the BX and MX transitions. Finally, by introducing QSs within perovskite matrices, we achieved a strong electroluminescence enhancement in light-emitting devices, yielding devices as bright as 213 W/m2 and a 2.3-fold enhancement of the maximum external quantum efficiency. These results represent a major step toward realizing solution-processed colloidal lasers and LEDs.