Researchers have achieved electrically switchable photoexcited pyroelectricity across a broad spectral range in a two-dimensional perovskite ferroelectric, (4-ethylanilinium)₂(ethylammonium)₂Pb₃Br₁₀, enabling room-temperature, self-powered light detection from ultraviolet (UV) to long-wave infrared (LWIR) wavelengths. The material can detect light from 266 nm to 12.5 μm, including the LWIR region.

The study, led by Prof. SUN Zhihua from Fujian Institute of Research on the Structure of Matter (FJIRSM) of Chinese Academy of Sciences (CAS), was published in Angewandte Chemie International Edition.

Broadband photodetectors that operate from UV light to LWIR radiation are important for environmental sensing, security, medical diagnostics and intelligent imaging. Most conventional photodetectors, however, rely on bandgap-mediated carrier excitation, which restricts the spectral range available from a single material and often makes LWIR detection dependent on cryogenic cooling.

Photoexcited pyroelectricity offers a different route. Instead of generating a signal through direct interband excitation, incident light produces a transient temperature change that modulates the spontaneous polarization of a ferroelectric. This light-heat-electricity conversion can therefore extend photoresponse beyond the material's optical absorption edge while supporting zero-bias operation.

In this study, the researchers investigated a two-dimensional perovskite ferroelectric, (4-ethylanilinium)₂(ethylammonium)₂Pb₃Br₁₀. They found that the hybrid perovskite adopts a polar trilayered Ruddlesden–Popper structure at room temperature and undergoes a reversible ferroelectric-to-paraelectric transition near 390 K. Piezoresponse force microscopy and polarization–electric field measurements confirmed reversible domain switching, while the polarization retained its performance after 10⁶ switching cycles.

Under illumination, reproducible pyroelectric currents were recorded continuously from 266 nm in the UV region to 12.5 μm in the LWIR region, far beyond the 2.69 eV optical bandgap. Reversing the ferroelectric polarization reversed the output current without substantially changing its magnitude. The electrically programmed signal state remained stable for more than 6 hours, demonstrating nonvolatile and controllable photoresponse.

A crystal-based device operated at room temperature without an external bias or cryogenic cooling. Under 10 μm irradiation, it detected a temperature variation as small as about 0.1 K and delivered a responsivity of 0.42 μA W^-1, a specific detectivity of 10⁵ cm Hz^1/2 W^-1 and a response time of approximately 80 ms. The photoresponse remained stable over 200 switching cycles.

To demonstrate practical sensing, the team fabricated a single-crystal array device that directly detected human-body thermal radiation. The zero-bias output decreased systematically as a finger was moved farther from the device, and tests with thermal sources at different temperatures further verified reliable room-temperature infrared sensing.

According to the researchers, this work provides the first demonstration of electrically switchable photoexcited pyroelectricity across the investigated UV-to-LWIR spectrum in a perovskite ferroelectric. It offers a material strategy for self-powered, uncooled and ultrabroadband detectors as well as future intelligent thermal-sensing systems.

Full-wavelength switchable photoexcited pyroelectricity in a perovskite ferroelectric (Image by Prof. SUN Zhihua's group)