Unraveling the Exciton Fine Structure of Strongly Confined 1D and 2D Halide Perovskite Nanocrystals

Recently, single photon emission was demonstrated for the first time in standard 3D lead halide perovskite (LHP) nanocrystals (NCs).^1–3 For quantum-confined LHP nanostructures, such as 2D nanoplatelets (NPLs) and 1D nanowires (NWs), however, such single emitter studies have hitherto remained scarce,⁴ possibly due to generally lower photoluminescence quantum yields and increased instability in these structures compared to the 3D NCs⁵. This limits the full exploration of LHPs with different dimensionalities as single photon emitters. Consequently, critical structure-property relationships cannot be unraveled.<br/>By treating our low-dimensional LHP NCs post-synthetically with a novel ligand, the optical properties of our 2D CsPbBr₃ NPLs and 1D CsPbBr₃ NWs are enhanced substantially. We observe an up to 2.5- and 7-fold enhancement of the photoluminescence quantum yield for the three-monolayer thick NPLs and NWs, respectively, in comparison to the untreated NPLs and NWs prepared with standard oleylamine and oleic acid ligands. Strikingly, we observe that the post-synthetic ligand treatment makes these highly confined NCs stable enough to enable deterministic single NC spectroscopy and measurement of their exciton fine structure for the first time.<br/>Consequently, with our results, we widen the available knowledge on the energetic structure of different-dimensional LHP NCs and pave the way to uncover crucial structure-optical property relationships to ultimately enable next-generation LHP quantum communication technologies.<br/> <br/>References:<br/>(1) Park, Y.-S.; Guo, S.; Makarov, N. S.; Klimov, V. I. Room Temperature Single-Photon Emission from Individual Perovskite Quantum Dots. <i>ACS Nano</i> <b>2015</b>, <i>9</i> (10), 10386–10393. https://doi.org/10.1021/acsnano.5b04584.<br/>(2) Rainò, G.; Nedelcu, G.; Protesescu, L.; Bodnarchuk, M. I.; Kovalenko, M. V.; Mahrt, R. F.; Stöferle, T. Single Cesium Lead Halide Perovskite Nanocrystals at Low Temperature: Fast Single-Photon Emission, Reduced Blinking, and Exciton Fine Structure. <i>ACS Nano</i> <b>2016</b>, <i>10</i> (2), 2485–2490. https://doi.org/10.1021/acsnano.5b07328.<br/>(3) Hu, F.; Zhang, H.; Sun, C.; Yin, C.; Lv, B.; Zhang, C.; Yu, W. W.; Wang, X.; Zhang, Y.; Xiao, M. Superior Optical Properties of Perovskite Nanocrystals as Single Photon Emitters. <i>ACS Nano</i> <b>2015</b>, <i>9</i> (12), 12410–12416. https://doi.org/10.1021/acsnano.5b05769.<br/>(4) Huo, C.; Fong, C. F.; Amara, M.-R.; Huang, Y.; Chen, B.; Zhang, H.; Guo, L.; Li, H.; Huang, W.; Diederichs, C.; Xiong, Q. Optical Spectroscopy of Single Colloidal CsPbBr3 Perovskite Nanoplatelets. <i>Nano Lett.</i> <b>2020</b>, <i>20</i> (5), 3673–3680. https://doi.org/10.1021/acs.nanolett.0c00611.<br/>(5) Bohn, B. J.; Tong, Y.; Gramlich, M.; Lai, M. L.; Döblinger, M.; Wang, K.; Hoye, R. L. Z.; Müller-Buschbaum, P.; Stranks, S. D.; Urban, A. S.; Polavarapu, L.; Feldmann, J. Boosting Tunable Blue Luminescence of Halide Perovskite Nanoplatelets through Postsynthetic Surface Trap Repair. <i>Nano Lett.</i> <b>2018</b>, <i>18</i> (8), 5231–5238. https://doi.org/10.1021/acs.nanolett.8b02190.