Broadband Pyro-Phototronic Effect in Lead-Free Double Perovskite Crystal Enables UV-to-NIR and Polarization-Sensitive Detection

Broadband spectral detection holds a significant promise for diverse applications in environmental monitoring, infrared sensing, and biomedicine. However, the photoresponsive ranges of most photoactive materials are often limited by the intrinsic optical bandgap, which predominantly focuses on the ultraviolet and visible spectral region, thus hindering their broadband optical applications. Therefore, achieving high-performance broadband spectral photodetection is essential for advancing various cutting-edge technologies. In this study, we have obtained a lead-free double perovskite (FPEA)₄AgBiI₈ (1, FPEA⁺ is p-fluorophenethylammonium), which has strong structural polarity and a narrow bandgap (E_g) of ∼1.80 eV. The π–π stacking of interlayer FPEA⁺ cations creates a robust interlayer connection that contributes to the growth of high-quality single crystals. Notably, the inherent polarity of 1 allows a broadband pyro-phototronic effect that covers a wide spectral range from the ultraviolet (UV, 377 nm) to the near-infrared (NIR, 2000 nm) region, breaking the limitation of its optical bandgap. This unique pyro-phototronic effect significantly enhances the photoelectric performance of 1, of which the photopyroelectric peak current at 637 nm illumination is 427% larger than the photovoltaic current. Additionally, combining the advantages of structural anisotropy and pyro-phototronic effect, the crystal-based device of 1 creates superior polarization-sensitive photodetection behaviors. This study not only enriches the portfolio of photoactive perovskite candidates but also provides an effective strategy for assembling high-performance optoelectronic devices.