2D Perovskites with Giant Excitonic Optical Nonlinearities for High-Performance Sub-Bandgap Photodetection

Two-dimensional (2D) perovskites have proved to be promising semiconductors for photovoltaics, photonics, and optoelectronics. Here, a strategy is presented toward the realization of highly efficient, sub-bandgap photodetection by employing excitonic effects in 2D Ruddlesden-Popper-type halide perovskites (RPPs). On near resonance with 2D excitons, layered RPPs exhibit degenerate two-photon absorption (D-2PA) coefficients as giant as 0.2-0.64 cm MW^{- 1} . 2D RPP-based sub-bandgap photodetectors show excellent detection performance in the near-infrared (NIR): a two-photon-generated current responsivity up to 1.2 × 10⁴ cm² W^-2 s^-1 , two orders of magnitude greater than InAsSbP-pin photodiodes; and a dark current as low as 2 pA at room temperature. More intriguingly, layered-RPP detectors are highly sensitive to the light polarization of incoming photons, showing a considerable anisotropy in their D-2PA coefficients (β_[001] /β_[011] = 2.4, 70% larger than the ratios reported for zinc-blende semiconductors). By controlling the thickness of the inorganic quantum well, it is found that layered RPPs of (C₄ H₉ NH₃ )₂ (CH₃ NH₃ )Pb₂ I₇ can be utilized for three-photon photodetection in the NIR region.