Selenium Alloying in CdSeTe Colloidal Quantum Wells as an Effective Strategy for High Efficiency and Enhanced Stability

CdTe colloidal quantum wells (CQWs) exhibit very low quantum yields (QYs) (<1%) and suffer significant stability challenges unlike their CdSe counterparts, which feature near unity QY and high stability under ambient conditions. Here, we synthesized highly stable CdSeTe CQWs with photoluminescence quantum efficiency (PLQY) reaching 25%, which far exceeds the previously best-reported PLQYs from CdTe CQWs while preserving the PL spectral characteristics (PL peak position and full-width-at-half-maximum (fwhm) of PL emission) similar to those of CdTe CQWs. In these as-synthesized CdSeTe nanoplatelets, a progressive increase in the Se/Te ratio leads to a notable enhancement in their quantum yield, accompanied by extended photoluminescence lifetimes, strongly indicating that higher Se incorporation effectively mitigates nonradiative recombination channels. In addition, we demonstrate that these CdSeTe CQWs are stable under ambient conditions unlike pristine CdTe CQWs through systematic studies with X-ray photoelectron spectroscopy (XPS). Using density functional theory (DFT) calculations we demonstrate that, under oxygen-rich conditions, O atoms weaken Cd–Te bonds and destabilize CdTe nanoplatelets, whereas in Se-alloyed CdSeTe CQWs, oxygen atoms preferentially adsorb onto the surface without penetrating the structure, effectively suppressing bond destabilization, which is consistent with our XPS observations. The enhanced optical properties, stability, and robustness of these CdSeTe-alloyed nanoplatelets offer a practical solution to overcoming the inherent limitations of CdTe CQWs and position them as highly attractive materials for practical use in advanced optoelectronic applications.