Metal‐Free Molecular Debye‐Type Relaxor Ferroelectric Crystals Enable Broadband Photo‐Pyroelectric Detection

Relaxor ferroelectrics have shown promising potential for various device applications, such as medical ultrasound transducers, pyroelectric infrared detectors, and electro-optic elements. Currently, relaxor ferroelectrics primarily consist of inorganic oxides, while achieving a pronounced relaxation in metal-free molecular ferroelectrics remains challenging due to the strong coupling between the relaxation mechanism and molecular dipole dynamics under applied electric fields. Consequently, this constraint leads to limited studies on their relaxation behavior and hinders progress in high-sensitivity applications, such as photo-pyroelectric detection. Here, Debye-type relaxation is unlocked in the molecular ferroelectric of bis(imidazolium) L-tartrate. In contrast to inorganic counterparts, this metal-free transparent single-crystal ferroelectric exhibits rare Debye-type dielectric relaxation arising from the molecular dipole reorientation that relates to the dynamic motion of organic imidazolium. Exceptionally, broadband photo-pyroelectric effects allow inch-size crystals for wide-spectral photodetection spanning UV to NIR-II wavelengths (266-1950 nm), breaking the conventional bandgap constraint on conventional materials. This work demonstrates that Debye-type relaxor molecular ferroelectrics are promising candidates for high-performance photo-pyroelectric detectors.