Preparation And Photovoltaic Property Studies Of Doped PZT-based Thin Films

Ferroelectric thin films have potential applications in ultraviolet-photovoltaic detection,photoelectric sensor and photovoltaic cells due to the presence of controllable photovoltaic properties.In recent years,PZT with higher residual polarization value is one of the most widely studied ferroelectric materials.Therefore, in this paper,the photovoltaic effect of PZT ferroelectric thin film is optimized by doping modification method.In the thesis, pure phase PZT films, PCZT thin films with different amounts of Co modified and PFZT thin films with different amounts of Fe modified have been prepared on Pt/Ti/Si O2/Si substrate by using sol-gel method and rapid thermal annealing process, respectively.The phase composition and microstructure of the films were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM).Analysis showed that all PZT thin films doped with Fe and Co display pure phase of perovskite and there was no other impurity phase.The PZT-based thin films that annealed at 650 ℃ have smooth surface, uniform size of the particles, clear cross-section and no crack generation.The ferroelectric and dielectric properties of PZT-based thin films were investigated systematicly. The results showed that all the PZT-based films were ferroelectric materials. The remnant polarization value of all PZT-based thin films decreased with the increase of doped contents,while the coercive field value increased at the same time;In the dielectric performance test,all PZT-based thin films showed dielectric tunability with well shaped butterfly loops and dielectric eliminate phenomenon.The leakage current of the doped thin films are higher than that of the pure phase PZT films.Compared with PFZT thin films,the improved effects of PCZT thin films were more obvious.From the Rayleigh and Boser formula of the film, the oxygen vacancies in PZT-based thin films increased gradually with the increase in content of transitional element Co and Fe.The photovoltaic performance of PZT-based thin films were investigated systematically.The results revealed that under dark condition, the original films(unpoled) show a weak photovoltaic response while has a pronounced photovolaic signal under light illumination condition and the photovoltaic response of doped films were higher than pure phase of PZT thin films.The influence of external electric field on the photovoltaic performance of thin film was obvious, and the phenomenon of photovoltaic effect reversed with applying-6V and +6V. Under thesame conditions, the photovoltaic response of the thin films with ITO top electrode is stronger than that of the thin films with Pt top electrode.Meanwhile,under light illumination with applying +6V, the maximum photocurrent and photoelectric conversion efficiency have been achieved on 15 mol% Co-modified PCZT thin film and 3 mol% Fe-modified PFZT thin film.The photocurrent values were 1.4×10-2μA 、 1.8×10-3 μA respectively and the photoelectric conversion efficiency were2.65×10-3%、5.56×10-4% respectively.Compared with PZT,the photocurrent and photoelectric conversion efficiency were increased by 1~2 orders of magnitude.