Bandgap-tuned barium bismuth niobate double perovskite for self-powered photodetectors with a full-spectrum response

Due to fascinating structural and compositional flexibility, double perovskite oxides A₂BB′O₆ with an alternating network of BO₆ and B′O₆ octahedra exhibit great potential for application in optoelectronic devices. In this work, the bandgap of Ba₂Bi_1+xNb_1−xO₆ (BBNO) is well tailored by precise control of the Bi : Nb ratio at B and B′ sites, leading to a broad absorption range from UV to NIR. A self-powered ITO/BBNO/Ag photodetector is fabricated based on the low-bandgap component of Ba₂Bi_1.5Nb_0.5O₆ (E_g = 1.37 eV), and displays greatly enhanced photocurrent and responsivity in a broad wavelength range from 365 to 760 nm. Particularly, the photodetector with Ba₂Bi_1.5Nb_0.5O₆ exhibits optimal performance with a photocurrent density of 59.2 μA cm⁻² and a photosensitivity of 78.8 μA W⁻¹ under 365 nm light, which is 60.5 times higher than that of a Ba₂BiNbO₆-based photodetector. Furthermore, it is found that the light-induced heat significantly enhances the photosensing properties, due to the temperature-modulated barrier height in the BBNO/ITO interface. This work demonstrates that precise control of the B : B′ ratio is an effective way to reduce the bandgap and achieve an excellent broadband photoresponse for double perovskite oxides A₂BB′O₆, which extends the application of double perovskite oxides in optoelectronics.