Defect-engineered black tetragonal-tungsten-bronze ferroelectric crystal for full spectrum absorption and broadband photoelectronic conversion.

Ferroelectric crystals have emerged as promising candidates for exotic optoelectronic platforms. However, the wide bandgaps of transparent ferroelectric crystals restrict their ultraviolet optical activity, hindering broadband photoelectric conversion. Herein, a hierarchical defect engineering strategy is proposed for ferroelectric oxides to achieve full-spectrum optical absorption and boost broadband self-powered photodetection. Based on the transparent calcium barium niobate crystal, red Ce:CSBN is designed through the cooperative isovalent substitution of Sr2+ and aliovalent substitution of Ce3+. Furthermore, a black Ce:CSBN crystal is fabricated via thermal reduction, which demonstrated ultra-broadband absorption from the ultraviolet to the mid-infrared range. This extended absorption capability is attributed to the judiciously modulated oxygen vacancies. Consequently, self-powered photodetection is realized in the 250-5000 nm range with a high responsivity of >1 mA/W, representing the widest responsive range among all-known ferroelectric detectors. More impressively, a reversible red-black transition is achieved by controlling oxygen vacancy concentration.