Two-Dimensional Layered Perovskites are Quasi 3D Semiconductors

Two-dimensional layered perovskites (2DLPs) have emerged as one of the most prominent candidates for next-generation optoelectronic applications due to their structural stability and tunable spacer design. However, the fundamental mechanism of carrier photogeneration remains unknown. Similar to other materials such as semiconductor quantum wells and transition-metal dichalcogenides (TMDCs), the primary mechanism is the formation of strongly bound excitons, as characterized by optical spectroscopies.<br/><br/>In this study, we observe free carrier generation in various spacer cation-based 2DLP structures, using both Pb and Sn, through ultrafast photocurrent spectroscopy with sub-25 picosecond time resolution. These 2DLPs exhibit carrier mobilities exceeding 3 cm2/Vs, exciton binding energies lower than those at room temperature, nearly 100% photogeneration quantum yield, and larger exciton Bohr radii. All these critical performance metrics are consistent with a dimensionality parameter greater than 2, suggesting these materials behave more like quasi-3D structures rather than exhibiting strong quantum confinement, as seen in typical 2D materials.<br/><br/>Our findings establish that 2DLPs with low-dielectric-constant spacer environments are quasi-3D materials. This work lays the foundation for the application of 2DLPs in a variety of optoelectronic devices, including solar cells, LEDs, photodetectors, and x-ray detectors.