Bandgap engineering and enhancing photovoltaic effect in NBT–BNT–xNd lead-free ceramics

The influence of Nd dopant on the photoelectric properties of 0.94Na_0.5Bi_0.5TiO₃–0.06BaNi_0.5Ti_0.5O₃–xNd ceramics were systematically investigated in this work. As the Nd³⁺ increases, the grain size gradually decreases and the crystal structure transforms from orthorhombic to tetragonal phase. Meanwhile, the dielectric constant and Curie temperature of ceramics gradually decrease, accompanied by the enhanced dielectric relaxation. The decreasing grain size and relatively strong ferroelectric properties facilitate the separation of photogenerated charge carriers. Optical absorption spectra indicate the enhanced absorption over a wider spectral range with a decrease optical band gap from 3.18 to 2.81 eV caused by Nd³⁺ doping. The photocurrent density improves from 44 nA/cm² for the undoped sample to 105 nA/cm² for x = 0.05 sample under AM1.5 standard sunlight after 40 kV/cm high-electric-field polarizing. This result demonstrates that the Nd doped NBT–BNT ferroelectric ceramics have high potential for the application in next-generation solar cells.