Real Money Rummy on ferroelectric oxides are attracting large interest due to its multifunctional application potentials. Recently, ferroelectric photovoltaic effect got large attention due to the anomalous photovoltage and switchable photoresponse. However, the low absorption bandwidth of the ferroelectrics due to their large bandgap results in low photocurrent, and this necessitates the search towards tuning the bandgap for better absorption properties. There are few attempts in the literature to reduce the bandgap but at the cost of deteriated ferroelectric properties. This trade-off between bandgap tuning and ferroelectric polarization is an open problem in ferroelectric photovoltaics. The present work addresses this problem and demonstrates novel ferroelectric materials with low bandgap and considerable polarization. In this work, a bandgap-engineered ferroelectric material of the composition (1-x)BaTiO3-xBi(Ni2/3Nb1/3)O3 (BTBNN) with x = 0 to 0.05 has been chosen for this study. The BTBNN samples exhibit wide bandgap tuning from 3.1 eV to 2.4 eV for doping variations of x = 0 to 0.05, with considerable room temperature polarization and open circuit photovoltage of 6 V. The reduction in bandgap is analysed with respect to structural distortion associated to the cationic and oxygen vacancies. Our results suggest that the samples with large cationic vacancies show better absorption properties with less leakage characteristics than those with more significant oxygen vacancies. This part of the work provides an alternative approach to to design the low bandgap ferroelectrics by means of cationic vacancies in the system. In addition, the ferroelectric system with optimized composition is fabricated into a polycrystalline and epitaxial thin film geometry. The film structures are subjected to photovoltaic and photodetector characteristics. These results will be discussed in this seminar
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