Free Charge Carrier Generation within Optically Confined Two-dimensional Perovskites

Two-dimensional hybrid organic inorganic perovskite (2DHOIPs) demonstrates promising optoelectronics applications, as compared to their 3D counterpart, despite their high excitonic binding energy (» hundred meV). However, the underlying exciton dissociation and the corresponding free carrier photogeneration mechanism remain unclear. Here lies the importance of this work, where we study the in-situ ultrafast electrical properties of 2DHOIPs based photoconductive thin film devices by manipulating the quantum confinement and the dielectric matching effect under the 25-ps based time resolutions. In contrast to widely used optical spectroscopic techniques including pump-probe and fluorescence approaches to investigate carrier diffusion dynamics, we have used the novel ultrafast photocurrent spectroscopy to investigate the carrier drift dynamics.[i] We found that those diverse 2DHOIPs including tunability of heterojunction (i.e., type-I or type-II), structural composition (i.e., Pb or Sn), organic ligand length, and the perovskites well layer thickness, essentially are quasi-3D semiconductors. This is confirmed by their temperature-independent high carrier mobility, near-unity quantum photogeneration efficiency, below room temperature exciton binding energy (~25 meV), and approaching 3D space factor. These exceptional properties arise from the dielectric quantum matching effect between the inorganic perovskite well and organic barrier layer within 2DHOIPs, rather than defect states as discussed earlier by the different ultrafast optical methods. Importantly, these benefits are achieved without compromising materials stability, making 2DHOIPs ideal candidates for the next generation of quantum optoelectronics and nonlinear optical applications. [i]Kobbekaduwa, K.; Liu, E.; Zhao, Q.; Bains, J. S.; Zhang, J.; Shi,Y.; Zheng, H.; Li, D.; Cai, T.; Chen, O.; Rao, A. M.; Beard, M.C.; Luther, J.M.; and Gao, J. Ultrafast Carrier Drift Transport Dynamics in CsPbI3 Perovskite Nanocrystalline Thin Films. ACS Nano 2023, 17, 13997-14004.