Towards Non-Blinking Strongly Confined Perovskite Quantum Dots

Quantum information science has shown its capabilities to enable secure quantum communications. Single photon emitters (SPEs) emit photons one at a time and are fundamental elements of such transformative technologies. Quantum dots (QDs), an atom-like solid-state light source, can emit photons with high efficiency and thus become promising SPE materials. Colloidal cesium lead halide (CsPbX₃, X=Br, I) perovskite QDs are ideal for next-generation SPEs because of their high room-temperature luminescence efficiency and low-cost, scalable syntheses. Unfortunately, individual perovskite QDs show insufficient photostability and severe photoluminescence (PL) intensity fluctuations. These fluctuations, also called blinking, can lead to spectral shifts, change the fluorescence dynamics, and reduce the structural stability of perovskite QDs. This has greatly limited the spectroscopic studies for SPE developments. Unlike conventional CdSe QDs, due to the highly ionic crystal structure of perovskites, there is not yet an approach to produce a homogeneous Type-I core-shell structure for perovskite QDs that can efficiently suppress blinking.<br/><br/>One challenge of studying the ionic perovskite QDs is their relatively low ligand binding affinities. When preparing individual perovskite QD samples, QD colloids often need to be diluted, and the ligand can detach from the QD, introducing defects. As a result, individual perovskite QDs often show rapid PL intensity fluctuations accompanied by photodegradation. Many significant advances have been made to search for ligands that bind strongly with the surface of perovskite QDs, such as zwitter ionic and didodecyldimethylammonium bromide ligands. However, perovskite QDs, especially for strongly size confined QDs, are still experiencing severe PL blinking with large PL “OFF” occurrences.<br/><br/>Here we discovered a method that can significantly suppress PL blinking and improve photostability of strongly confined CsPbBr₃ Perovskite QDs. CsPbBr₃ QDs with tunable sizes from ~ 3.5 nm to 7 nm are synthesized using the thermodynamic-equilibrium-controlled method and annealed at elevated temperatures to form a bromide rich surface. Diluted QD colloids are then used as antisolvent and nucleation centers to form a polycrystalline thin film consisting of phenethylammonium bromide (PEABr) salts. The bromide rich surface will be epitaxially anchored onto the PEABr matrix and therefore be passivated. Individual strongly confined CsPbBr₃ QDs embedded in the PEABr show nearly non-blinking behavior under both pulsed and <i>cw</i> aser excitations (non-resonant) at room temperature. Power-law analysis of the blinking traces of thes perosvkite QDs show very different “ON” and “OFF” powers (0.85 and 1.9). These QDs remain photostable for more than one hour under laser excitations and show very high singe photon purities (&gt; 95%). Additionally, CsPbBr₃ QDs with sizes from 3.5 nm to 7 nm can all be passivated and stabilized using our method and show nearly non-blinking behaviors. We anticipate that these QDs will result in more accurate and detailed studies of exciton dynamics and structural-optical property relationships in strongly confined perovskite QDs.