The Modulation Of Photovoltaic For BiFeO₃ And CdS Films

Currently,ferroelectric and piezoelectric materials have been subjected to intensive research due to their rich physical content and potential application.The photovoltaic effect of the device can be modulated by ferroelectric polarization and piezophototronic effect.Accordingly,devices with specific functionality and application scenarios such as information storage and human-machine interface may have been developed in near future.The photovoltage of ferroelectric material can exceed the limitation of bandgap.However,the small photocurrent density limits the photoelectric conversion efficiency of the device.Many ways have been explored to enhance the photovoltaic properties of ferroelectric materials,hoping to make these materials promising and to develop new functional devices.On the other hand,due to the piezoelectric effect of piezoelectric materials,piezoelectric potential can be used to induce the change of band structure of the PN junction or Schottky junction and regulate the barrier height of the junction region,thereby strengthening or weakening photovoltaic output.Surrounding these two research directions,the main content of this paper is as follows:?1?In Chapter 3,photovoltaic?PV?effect of ferroelectric Bi_0.85La_0.15FeO₃?BLFO?films fabricated through the sol-gel method has been investigated.Compared to BiFeO₃?BFO?thin film,photovoltaic effect of BLFO thin film has been significantly improved.La doping not only reduces optical bandgap of BFO thin film but also produce structure distortion,resulting in improve the ferroelectric property of the film.BLFO thin films with macroscopic ferroelectric properties exhibit polarization-tunable photovoltaic effects.The gold nanoparticles?AuNPs?were modified on the surface of the BLFO film by DC sputtering.The application of AuNPs increases the open circuit voltage(V_OC)and short circuit current density(J_SC)from0.2 V to 0.3 V and 5.3?A/cm² to 18.5?A/cm² respectively,which can be attributed to Au surface-plasmon effects.At the same time,ferroelectric polarization can also modulate the gold nanoparticle-modified BLFO thin film photovoltaic effect.For the ITO/AuNPs/BLFO/FTO device,it is obvious that the V_OC and J_SCC for the-10 V poled,unpoled and+10 V poled are 0.37 V and 11.4?A/cm²,0.3 V and 18.5?A/cm²,0.4V and 20?A/cm²,respectively.It can be seen that the positive polarization enhances the photovoltaic effect and the negative polarization weakens the photovoltaic effect.For ITO/AuNPs/BLFO/FTO devices,UV-visible absorption spectroscopy shows that AuNPs can indeed produce surface plasmon effects.Under the synergistic action of AuNPs plasmon and+10 V poled,the open circuit voltage increases from 0.2 V to0.4 V,and the short-circuit current density increases from 5.3?A/cm² to 20?A/cm².The corresponding modulation rates are 100%and 277%,respectively.We propose a reasonable theoretical model to explain it.This work has enhanced the photovoltaic performance of the lead-free ferroelectric thin film by the surface plasmon effect for the first time.The highlight is that the surface plasmon effect gives obvious experimental evidence.This work not only presents a new method for improving the photovoltaic effect of ferroelectric thin films,but also provides an important perspective for understanding the physical mechanism of the photovoltaic effect of ferroelectric thin films.?2?CdS is one of popular piezoelectric semiconductors.CdS nanowire arrays?CdS NWs?were prepared by hydrothermal method on FTO conductive glass.The XRD results showed that the CdS was pure phase and preferred growth along the c axis.The morphology of CdS was characterized by SEM,which illustrated that the length of CdS NWs were 600 nm and diameter were 176 nm.The CdS nanowire arrays were integrated with the organic polymer P3HT to form a heterojunction and the photovoltaic properties of the device were studied.The influence of the piezoelectric effect for the device on the photovoltaic output was initially explored.The experimental results showed that the compressive stress reduced the photovoltaic output of FTO/CdS NWs/P3HT/Ag devices,and a theoretical model has been proposed to explain the experimental result.It is essential to further optimize the device structure and improve the photovoltaic performance.