In atomically thin 2D crystals, the excitonic properties and band structure scale strongly with the thickness, providing a new playground for the investigation of exciton physics in the ultimate confinement regime. We demonstrate the evolution of the fundamental excitonic properties, such as reduced mass, wave function extension and exciton binding energy, in the 2D perovskite (PEA)2(MA)n-1PbnI3n+1, for n=1,2,3. These parameters are experimentally determined using optical spectroscopy in high magnetic field up to 65 T. The observation of the inter band Landau level transitions provides direct access to the reduced effective mass μ and band gap Eg. We show that μ increases with the number of inorganic sheets n, reaching the value of 3D MAPbI3 already for n=3 (see Figure). Our experimental observations contradict the general expectation that quantum confinement leads to an enhanced carrier mass, showing another aspect of the unprecedented flexibility in the design of the electronic properties of 2D perovskites.
Publication - Tuning the Excitonic Properties of 2D (PEA)2(MA)n−1PbnI3n+1 Perovskite Family via Quantum Confinement - M. Dyksik, S. Wang, W. Paritmongkol, D. K.Maude, W. A. Tisdale, M. Baranowski, and P. Plochocka, J. Phys. Chem. Lett. 12 (6), 1638 (2021)
Figure - Evolution of the reduced effective mass μ with increasing number of inorganic sheets. Insets show the schematics of each sample (c axis pointing upwards): black and open spheres stand for Pb and I atoms and build the inorganic framework; phenyl ring with ammonia group is the large organic spacer L (PEA, C6H5C2H4NH3). For clarity the small organic cation (MA, methylammonium) filling the octahedral voids is omitted.