Bi5FeTi3O15 (BFTO) and BFTO/CuO films were deposited by a sol-gel technique, which exhibited macroscopic ferroelectric properties. It was found that the BFTO/CuO films showed a short circuit photocurrent density (Jsc) enhanced by nearly 10 times and power conversion efficiency increased by 13-fold compared to those of the BFTO film. The significant increase in the photovoltaic (PV) response may be attributed to the p-n junction internal electric field acting as the driving force of photogenerated carriers. Furthermore, both BFTO and BFTO/CuO films indicated a switchable PV response in both polarities. The open circuit voltage (Voc) and Jsc for BFTO and BFTO/CuO were observed to be −0.59 V and +43.88 μA/cm2 and −0.23 V and +123.16 μA/cm2, respectively, after upward poling, whereas after downward poling, +0.11 V and −6.26 μA/cm2 and +0.17 V and −83.21 μA/cm2 for BFTO and BFTO/CuO were observed, respectively. The switchable PV responses were explained by the ferroelectric depolarization field, whose direction could be altered with the variation in the applied poling field. This work provides an efficient approach to developing ferroelectric film based PV devices with low cost.

Previous experiments showed that Hf/Sb co-doping in ZrNiSn impressively improved the electrical conductivity (σ). To explore the physical reasons for this improvement, the electronic structures of HfxZr1−xNiSn1−ySby (x = 0, 0.25, 0.5; y = 0, 0.02) have been systematically investigated by using the first-principles method and semiclassical Boltzmann transport theory. 50% Hf doping at Zr site in ZrNiSn simultaneously increases the degeneracy and dispersion of energy bands near the conduction band edge, which are helpful to optimizing Seebeck coefficient and slightly improving σ. Furthermore, 2% Sb co-doping at Sn site in Hf0.5Zr0.5NiSn not only increases total density of states near the Fermi energy but also retains high mobility, and N v reaches eleven at the conduction band minimum, thereby inducing a large improvement in σ. Additionally, the Bader charge analysis shows the reason why Sb co-doping supplies more electrons. It is most likely derived from that Sb loses more electrons and Sb-Ni has a stronger hybridization than Sn-Ni. Moreover, we predict that the ZT of Hf0.5Zr0.5NiSn0.98Sb0.02 at 1000 K can reach 1.37 with the carrier concentration of 7.56 × 1018 cm−3, indicating that Hf/Sb co-doping may be an effective approach in optimizing thermoelectric properties of ZrNiSn alloy compounds.