Fabrication And Photovoltaic Properties Of Pure And Doped Hexagonal Ferroelectric Manganite Thin Films

Ferroelectric photovoltaic(FE-PV)materials with narrow optical band gap,good carrier transportation and strong visible-infrared absorption,have attracted more and more attention from domestic and foreign researchers.FE-PV materials also have the advantages of mechanical,chemical,and thermal stability,and low cost.Therefore,they are used in solar energy conversion applications.As a unique photovoltaic(PV)material system completely different from the traditional p-n junction PV effect,on the one hand,the photocurrent direction of FE-PV materials can change with the change of the spontaneous polarization direction.On the other hand,it has an abnormal PV effect that the output photovoltage along the polarization direction is much larger than its band gap,up to 10⁴ volts.These unique physical behaviors broaden the application fields of FE-PV materials.This research takes the narrow band gap h-YMnO₃-based ferroelectric thin film material as the research object,studies its photovoltaic and photodetection performances under different light and temperature fields,and preliminary discusses its photoelectric response mechanism,and realizes the innovation of FE-PV material system.In this paper,firstly,a high-quality h-YMnO₃ FE thin film material was prepared by sol-gel method,and its phase structure,morphology,optical properties,electrical properties,and PV and photodetection properties were tested.The experimental results show that the polycrystalline hexagonal FE thin film can obtain excellent PV and photodetection performances,and the photocurrent density of the positive voltage polarized FE thin film can reach 3.92 mA/cm² under the light intensity of 100 mW/cm².FE polarization and grain boundaries play a very important role in the FE-PV effect.In order to further improve the PV performance and obtain excellent photodetection performances of the h-YMnO₃ thin film material,Bi-doped YMnO₃ thin films were prepared on Si substrate by the sol-gel method,and the PV performances were used.The system measures its PV and photodetection performance and the enhanced mechanisms for its performance were explored.The self-powered photodetector based on Y_0.95Bi_0.05MnO₃ thin film material as the light absorption layer can obtain a responsivity of 0.64 A/W,a detectivity of 8.37×10¹³ Jones,and response time of 8.6/9.3 ms under 5 mW/cm² light intensity,which are higher than other self-powered photodetectors based on other PE materials as the light absorption layer.At the same time,photodetection performances have also been studied under monochromatic light.The responsivities of monochromatic light at 405,650,780 and 808 nm are 0.48,0.46,0.36,and 0.24A/W,respectively,and the corresponding detectivities are 6.22×10¹³,5.96×10¹³,4.8×10¹³,and3.15×10¹³ Jones,respectively.Based on the above optimal component,the performances of self-powered photodetector have been studied at high temperatures.In this experiment,the photocurrent density versus time curve of the detector at three different temperatures was tested,and the current density at different temperatures show excellent stability and repeatability.We also characterized its responsivity,detectivity,and response time under sunlight and monochromatic light.The corresponding responsivity at test temperatures of 323,343 and 363 K are 0.28,0.17,and 0.06 A/W.The detectivity at the test temperature of 323 K is 9.92×10¹² Jones,and the detectivity at the other two test temperatures are in the order of 10¹¹.