The Impact of Structure in Achieving Optically Efficient One-Dimensional Lead Halide Perovskite Nanostructures

Metal halide perovskites have gained significant attention due to their outstanding optoelectronic properties. In 2015, our group debuted the first one-dimensional (1D) colloidal CsPbBr₃ nanostructures following the initial report of CsPbBr₃ quantum dots (QDs). In the past decade, while the traditional zero-dimensional QDs have achieved near-unity photoluminescence quantum yield (PLQY) through surface passivation, the opposite is true for 1D perovskites, such as nanowires (NWs, aspect ratio: >300) and nanorods (NRs, aspect ratio: 10-20). More importantly, a fundamental understanding of their structure-property correlations remains incomplete. This work investigated structure-property correlations in size- and shape-controlled CsPbBr₃ nanocrystals to elucidate the effect of quantum confinement and dimensionality on their optoelectronic properties, culminating in the achievement of highly emissive 1D CsPbBr₃ with high to near-unity PLQY and faster recombination rates relative to QDs. We synthesized morphologically pure and thickness monodisperse QDs, NWs, and NRs, consisting of weakly confined green emitters (> 7 nm-thick) and strongly confined blue emitters (<5 nm-thick). High to near-unity PLQY values of 99 ± 3% for 8 ± 1 nm QDs, 72 ± 2% for 8 ± 1 nm NWs, 79 ± 1% for 3.2 ± 0.1 nm NWs, 78 ± 3% for 3.2 ± 0.1 nm NRs, and 97 ± 2% for 2.4 ± 0.1 nm NRs were achieved without relying on any additional surface passivation techniques. These PLQY values were tied to the PL decay and apparent radiative rates (k_r) of the nanostructures, as determined by temperature-resolved time-correlated single photon counting PL spectroscopy. The 8 nm NWs exhibited slower PL decay and k_r values due to enhanced exciton diffusion along their 1D structure, which facilitated exciton trapping and detrapping processes, along with significantly faster nonradiative recombination rates (k_nr) relative to QDs of the same diameter. For the strongly confined systems, exciton diffusion was limited by fast radiative recombination, preventing access to additional trap states and contributing to near-unity PLQY. Additionally, comparable k_r, k_nr, and PLQY values between the 3.2 nm NWs and NRs showed that the length of 1D CsPbBr₃ has minimal influence on exciton diffusion under strong confinement. Furthermore, the 2.4 nm NRs were 3.6X brighter than the traditional 8 nm QDs because of their comparatively fast k_r. We find that the origin of enhanced radiative recombination in strongly confined 1D perovskite comes from both, an increase in quantum confinement and oscillator strength. Interestingly, the latter increases with aspect ratio below the exciton Bohr diameter according to electronic structure calculations, underscoring a key advantage of 1D perovskite over QDs. In addition to elucidating the effect of dimensionality, these findings demonstrate how, through a model system, there is room to boost the optical performance of perovskites via structural and morphological optimization, providing key insights into potential applications for optoelectronic devices. Finally, this talk will highlight opportunities in other unexplored facets of 1D perovskite, such as anion exchange, stability, and chiroptical properties.