Photovoltaic Device Construction And Mechanism Research Based On Two-dimensional Ferroelectric Materials

Ferroelectric materials have polarization that can be switched by electric field,so they are widely used in the fields of non-volatile memory,energy conversion and neural morphology calculation.Ferroelectric photovoltaic has much higher open-circuit voltage than bandgap and high photoelectric conversion efficiency,so it has great research value and potential application prospect in the field of new energy photovoltaic technology.However,the physical mechanism of ferroelectric photovoltaic effect is not clear at present.According to the different structures of ferroelectric materials and devices,due to the factors such as electrode interface and depolarization field,many possible physical models have been proposed to explain the ferroelectric photovoltaic effect,such as bulk photovoltaic effect,depolarization field effect,and domain wall effect.All kinds of mechanisms are closely related to ferroelectric polarity.The two-dimensional van der Waals layered ferroelectric materials with atomic thickness have no hanging bond interference and maintain stable ferroelectric polarization in nanometer thickness,so they are of great research value in nano-sized ferroelectric optoelectronic devices in the post-Moore era.As one of the most representative two-dimensional ferroelectric materials,CuInP₂S₆ has stable out-of-plane polarization at room temperature and unique ferroelectric and ion coupling characteristics,which provides an ideal platform for studying the physical mechanism of ferroelectric photovoltaic effect.Based on this,a photovoltaic device based on CuInP₂S₆ is constructed,the switchable photovoltaic characteristics of van der Waals layered ferroelectric are studied systematically,and the physical mechanism of ferroelectric polarization and ion migration coupling effect on ferroelectric photovoltaic is discussed in detail.The specific research contents are as follows:（1）The photovoltaic effect of CuInP₂S₆ is studied systematically,and the action mechanism of ion relaxation effect and bulk photovoltaic effect is clarified.The time-dependent variation of photogenerated short-circuit current in CuInP₂S₆ under different polarization states is investigated experimentally,in which the initial peak photocurrent and steady-state photocurrent show opposite polarity directions.The process of initial photocurrent produced by the relaxation effect of van der Waals interlayer Cu ions is studied and analyzed,and the relationship between polarization-dependent bulk photovoltaic effect and steady-state photocurrent is analyzed.This work provides a research idea for understanding the ionic ferroelectric photovoltaic effect.（2）The physical mechanism of the unique quadruple-well energy distribution of CuInP₂S₆ affecting the ferroelectric photovoltaic properties was thoroughly studied.A device with phase separation characteristics is obtained by using a large electric field to drive the redistribution of Cu ions.The quadrupole states of±HP and±LP corresponding to its quadruple-well potential are confirmed by the results that the shift current is regulated by triangular waves.By applying a polarized electric field with fixed direction and different pulse width,the variation of photogenerated short-circuit current with the pulse width of electric field is investigated.The bulk photovoltaic effect characteristics corresponding to the quadrupole state are analyzed,and the relationship between the polarization switching process and the bulk photovoltaic effect current is clarified.This work provides an experimental basis for further study of the polarization origin and dynamic process of CuInP₂S₆ bulk photovoltaic effect.（3）The reconfigurable optically controlled ferroelectric polarization reversal is studied and realized.The distribution of Cu ions in the CuInP₂S₆ lattice layer is regulated by applying a polarized electric field during the heating process,and the initial device state of the homogenous p-n junction is realized,which is confirmed by the electrical rectifying characteristics of the device.The variation of photogenerated short-circuit current under different initial polarization states is studied systematically,and the working mechanism of photo-regulated ferroelectric polarization reversal is revealed.This work provides a new design idea for the development of nano-optoelectronic devices with remote contactless control.