热硫化Co掺杂对纳-微米黄铁矿的晶体结构特征及光吸收性能的影响

Influence of Doping Co Amount on the Crystal Structure Characteristics and Light Absorption Properties of Nano-Micrometer Pyrite Prepared by Thermal Sulfide Method

过渡金属硫化物黄铁矿是一种优异的光伏材料,掺杂改性是提高黄铁矿光伏性能的一种重要手段。为了探究不同Co掺杂量对黄铁矿的晶体结构和吸光性能的影响,采用热硫化法在360℃时制备出了纳-微米黄铁矿样品。利用X射线衍射(XRD)和多功能场发射扫描式电子显微镜(FESEM)分析了样品的晶体结构、形貌特征和晶粒尺寸;利用能谱仪(EDS)分析了样品的化学成分,并通过紫外-可见-近红外分光光度计(UVVis-NIR)表征了样品的光吸收性能和禁带宽度的变化。结果表明,掺Co并未改变黄铁矿的立方晶型结构,但与未掺杂黄铁矿相比,样品结晶度变差,晶粒发生团聚,尺寸在1~1.45μm范围内;掺Co量的增加会导致晶粒尺度略微减小,但影响不大。EDS检测表明,实际样品的掺杂并不均匀,当掺Co量小于7at%时,测试值小于名义掺杂量;而当掺Co量大于7at%时,Co易发生富集。S/(Fe+Co)的比值在1.92~2.05范围内,表明样品内部的点缺陷数量的变化。反射光谱表明制备样品的禁带宽度Eg在0.57~0.72eV之间。禁带宽度Eg随着掺杂量的增加,呈现出先减小(Co 3at%)后增加(Co 5~9at%)的趋势。掺Co量从0%增加3at%时,样品内部产生的点缺陷数目增多,形成的附加能级会导致禁带宽度Eg窄化;随着掺Co量进一步增加,S/(Fe+Co)比值更接近于2,晶体结构更趋完善,Fe空位或S间隙点缺陷比率降低,禁带宽度Eg趋近于本征特征,会导致禁带宽度Eg宽化;另外,随着Co含量的提高,物相中微量的CoS2相增多,亦会导致较高掺Co量样品的禁带宽度有所宽化。掺Co量在9at%的样品的禁带宽度为0.72eV,大于同温度条件下未掺杂样品的禁带宽度0.65eV,禁带宽度的宽化在理论上有利于提高样品的光电转换效率。

Transition metal sulfide pyrite is a kind of excellent photovoltaic material,doping modification is an important mean to improve the properties of pyrite PV.To explore the impact of Co-doped amount on pyrite crystal structure and light absorption performance,nano-micron-sized pyrite samples were prepared via thermal sulfide method at 360 ℃.In addition,the crystal structure,morphology characteristics and grain size of samples were analyzed with X-ray diffraction（XRD）and multi-functional field-emission scanning electron microscope（FESEM）.Moreover,the chemical composition of the samples was tested using the energy dispersive spectrometer（EDS）,the light absorption performance and the change of the forbidden band width of the samples were characterized through the ultraviolet-visible-near infrared absorption spectroscopy（UV-Vis-NIR）.The results of XRD and FESEM indicated that co-doped led to crystallinity changes,crystal grain reunion,larger size in the range of 1～1.45μm,but did not change the cubic crystal structure of pyrite,compared with pyrite samples without doping.The grain size decreased slightly with the increasing amount of co-doped,but the impact was not obvious.EDS test showed that the actual samples doping was not uneven,the test value was less than the nominal doping Co amount when amount of co-doped was less than7 at%,while it was larger than nominal when doping Co amount was greater than 7 at%.The ratios of S/（Fe＋Co）were within the scope of 1.92 to 2.05,the degree of deviation 2 of the ratio suggested the number change of point defect of internal samples,affecting the light absorption performance of the samples.Besides,reflection spectrum showed that band gap Eg was from 0.57 to 0.72 eV.The width of forbidden band reduced（Co3 at%）before it increased as doping Co amount increased（Co5～9 at%）.The additional energy level,formed by a number of point defects in internal samples,led to band gap narrowing,as mixing amount of Co increased from 0% to 3 at%.With further increasing mixing amount of Co,S/（Fe＋Co）ratio was closer to 2,the crystal structure was more perfect and the Fe vacancy or S clearance point defect ratio was more decreased,leading to the forbidden band width Eg tend to widen.In addition,with the increase mixing amount of Co,the increasing trace CoS2 phase caused the forbidden band width to larger,up to 0.72 eV,as the mixing amount of Co further increased to 9 at%,which was greater than the forbidden band width of 0.65 eV of not doped samples at the same temperature,the same synthetic methods,in theory,which could effectively improve the photoelectric conversion efficiency.