Circular and linear polarized reflectivity of intra-plane and inter-plane excitons in 2D phenethylammonium lead iodide single crystal*

2D phenethylammonium lead iodide (2D-PEPI), being an exemplary 2D hybrid organic-inorganic perovskites having Ruddlesden-Popper structure, has attracted substantial research interest. Having a natural multiple quatum well (MQW) structure with interdigitated organic and inorganic layers, 2D-PEPI has tunable band structure. 2D-PEPI also possesses strong spin-orbit coupling (SOC) owing to the inclusion of the ‘heavy atom’ lead (Pb), with the presence of inversion symmetry breaking that may originate from structural imperfections and interfaces, giant Rashba splitting was reported by spin related circular photogalvanic effect (CPGE). Due to quasi-2D quantum and dielectric confinements, the excitons in 2D-PEPI are tightly bound with binding energy on the order of a few hundreds meV. Two types of excitons co-exist in 2D-PEPI, namely the free exciton and bound exciton associated with edge states. In this work, we measure polarized photoluminescence and reflectivity and CPGE of 2D-PEPI single crystal and confirm that the free exciton is in the MQW plane, whereas the bound exciton possesses an out-of-plane dipole moment. By comparing the results from circular polarized reflectivity with the CPGE current, we show that the spin-polarized current in 2D-PEPI originates from the interplane bound exciton, while the intraplane free exciton does not produce such current. Our finding is important to guide the design of a cost-effective MQW spintronic devices made from solution process.