In掺杂h-LuFeO3光吸收及极化性能的第一性原理计算

First principles calculation of optical absorption and polarization properties of In doped h-LuFeO

h-LuFeO3是一种窄带隙铁电半导体材料,已被证明在铁电光伏领域有较好的应用前景.然而,较低的极化强度使光生电子-空穴对复合率大,限制了h-LuFeO3基铁电光伏电池效率的提高.为改善h-LuFeO3的极化强度,提高光吸收性质,本文利用第一性原理计算方法研究了In原子在h-LuFeO3不同位置的掺杂形成能,得到最稳定的掺杂位置,比较了h-Lu1-xInxFeO3(x=0,0.167,0.333,0.667)的带隙、光吸收性能及极化强度等性质.计算结果表明,随着In掺杂比例的增加,h-LuFeO3的晶格常数c/a比不断增大,铁电极化强度得到提高.当In:Lu=2:1时,材料杂质能级出现,Fe-O轨道杂化得到增强,提高了h-LuFeO3的光吸收性能.此工作证明了In掺杂是改善h-LuFeO3极化强度和光吸收系数的有效方法,对铁电光伏性能的提高提供一种新途径.

The h-LuFeO3 is a kind of narrow band gap hexagonal ferrite material,with a good application prospect in the field of ferroelectric photovoltaic.However,the low polarization intensity of h-LuFeO3 makes the recombination rate of photogenerated electrons and holes large,which is not conducive to the improvement of the efficiency of h-LuFeO3-based ferroelectric photovoltaic cells.In order to improve the ferroelectricity and optical absorption properties of h-LuFeO3,the first principles method is used to calculate the doping formation energy values of In atom at different positions of h-LuFeO3,and the most stable doping position is determined.The comparisons of band gap,optical absorption performance and polarization intensity among h-Lu1-xInxFeO3(x=0,0.167,0.333,0.667)are made.With the increase of In doping,the cells of h-Lu1-xInxFeO3 stretch along the c-axis.The ratio of the lattice constant c/a increases from 1.94 at x=to 2.04 at x=0.667 when all the positions of In replace P1 position.Using the qualitative calculation of Berne effective charge,the results show that the ferroelectric polarization intensity of h-LuFeO3,h-Lu0.833In0.167FeO3,h-Lu0.667In0.333FeO3 and h-Lu0.333In0.667FeO3 along the c-axis are 3.93,5.91,7.92,and 11.02μC·cm-2,respectively.Therefore,with the increase of the number of In atoms replacing Lu atoms,the lattice constant c/a ratio of h-Lu1-yInxFeO3 increases,which can improve the ferroelectric polarization strength of the material.By analyzing the density of states of h-LuFeO3 and h-Lu0.333In0.667FeO3,we can see that In doping enhances the Fe-O orbital hybridization in h-Lu0.333In0.667FeO3,and makes the optical absorption coefficient of h-Lu0.333In0.667FeO3 in the solar light range larger.In summary,In doped h-LuFeO3 is an effective method to improve its polarization intensity and optical absorption coefficient,which is of great significance for improving the performance of ferroelectric photovoltaic.