Engineering Colloidal Quasi-2D Quantum Wells for High-Performance Room-Temperature Single-Photon Sources

Single-photon sources (SPSs) are essential for quantum technologies. Colloidal quasi two-dimensional (2D) quantum wells (QWs) possess high emission uniformity, photoluminescence quantum yields (PLQYs), and narrow linewidths at room temperature, all contributing to ideal SPSs. However, their large lateral dimensions make excitons sensitive to environments and enhance multiexciton emission, casting long-standing doubt on their viability as SPSs. Here, we demonstrate bright room-temperature single-photon emission (SPE) with high purity and minimal blinking from in-plane-engineered (IPE) 2D QWs incorporating a doubly gradient architecture. A compositionally graded CdSe/CdSe_xS_1-x core in the in-plane direction tailors electron-hole wavefunctions to control multiexciton Auger dynamics, while a graded Cd_yZn_1-yS shell in the thickness direction suppresses interfacial strain and nonradiative defects. This design unites 0D and 2D structural advantages, achieving near-unity ensemble PLQY and bright SPE (0.6-1.2 × 10⁵ counts/s, NA = 0.65). Controlling the CdSe core size via IPE, we attain 92% single-photon purity (2 nm core), and suppressed blinking with a 96.9% ON-time fraction (8 nm core). This work establishes deterministic design rules for colloidal 2D QWs as high-performance SPSs for scalable quantum technologies.