利用电沉积-溶剂热-硒化技术提高基于二硒化镍对电极的染料敏化太阳能电池的填充因子

Improved Fill Factor of Dye-sensitized Solar Cells with Nickel Diselenide Counter Electrode by Electrodeposition-Solvothermal-Selenization Technique

为了促进绿色可再生能源的开发利用,提高低成本染料敏化太阳能电池(DSCs)的光伏性能显得十分重要。对电极作为DSCs的重要组成部分,直接影响其光伏性能。针对硒化镍对电极的电催化性能及其光伏性能有待提高等关键问题,学者们已采用多种合成技术调控硒化镍的形貌与物相,从而提高硒化镍对电极的电催化性能。研究表明,二硒化镍(NiSe2)纳米材料由于具有较多的边缘活性位点而展现出较好的导电性与催化性能。然而,与基于铂电极的电池器件相比,基于NiSe2对电极的DSCs表现出相对较小的填充因子。本工作利用电沉积-溶剂热-硒化技术设计构建出一种新型NiSe2对电极。其中以氟掺杂二氧化锡(FTO)导电玻璃为基底,采用恒电势电化学沉积技术制备了Co(OH)2薄膜,并以其为生长点通过溶剂热法合成镍基金属有机框架(Ni-MOF)结构,进一步以硒粉为硒源在氩气环境下进行硒化处理制备NiSe2纳米材料。SEM、TEM、XRD与XPS测试结果表明:所制备的样品是由纯相NiSe2物相构成;NiSe2纳米材料呈现出颗粒状形貌,且平均粒径约为500nm;NiSe2纳米材料均匀生长在FTO导电玻璃表面上,可直接作为DSCs的对电极。循环伏安(CV)曲线、电化学阻抗谱(EIS)及塔菲尔(Tafel)极化曲线分析表明,NiSe2对电极展现出较窄的峰-峰间距,较小的串联电阻、电荷传输电阻、能斯特扩散阻抗以及较大的还原峰电流密度和交换电流密度,预示着NiSe2对电极具有良好的电催化性能。这是由于结晶度较高的纯相NiSe2纳米材料具有丰富的边缘活性位点;电沉积-溶剂热-硒化技术有效改善了NiSe2纳米材料在FTO导电玻璃上的附着强度,有利于电子的有效转移。此外,光电流密度-电压(J-V)曲线表明由NiSe2对电极组装的DSCs呈现出优异的光伏性能,其能量转换效率(PCE)高达7.63%,高于铂电极组装的DSCs(7.21%),其填充因子从0.65增大到0.70,可能是由于NiSe2对电极总电阻较小。本工作设计的新型NiSe2对电极不仅具有优异的电催化性能,还成功改善了基于NiSe2对电极的DSCs的填充因子,并有效提高了DSCs的光伏性能。

The photovoltaic performance of low-cost dye-sensitized solar cells (DSCs) should be further improved to promote the development and utilization of green renewable energy. The photovoltaic performance can be directly affected by counter electrode (CE) as an important part of DSCs. However,the photovoltaic performance of DSCs based on nickel selenides CE can be further improved. Therefore,the further enhance the electrocatalytic performances of nickel selenide CEs is one of the key scientific problems. To improve the electrocatalytic performances of nic-kel selenide CEs,various synthetic techniques have been used to control their morphology and phase. Specially,previous researches have shown that NiSe 2 nanomaterials exhibit good electronic conductivity and catalytic activity due to the more edge active sites. However,the DSC assembled from NiSe 2 CE shows the relatively smaller fill factor than that of the DSC assembled from platinum (Pt) CE. In this work,we have demonstrated the electrodeposition-solvothermal-selenization technique to design and fabricate NiSe 2 CE. The fluorine-doped tin oxide (FTO) glass was used as substrate to synthesize Co(OH) 2 films by a potentiostatic electrodeposition technique. The nickel me-tal-organic frameworks (Ni-MOF) were fabricated on the Co(OH) 2 films by solvothermal method. And then selenium powder was used as sele- nium source to prepare NiSe 2 nanomaterials in an argon atmosphere by selenization technique. The results from SEM,TEM,XRD patterns,and XPS spectra demonstrate that as synthesized samples are composed of the pure phase NiSe 2. NiSe 2 nanomaterials appear as irregular nanoparticles with the average size of about 500 nm. And NiSe 2 nanomaterials uniformly grow on the surface of FTO glass,which can be directly applied as CE of DSCs. NiSe 2 CE was characterized by cyclic voltammetry (CV) curves,electrochemical impedance spectroscopy (EIS),and Tafel polarization curves to analysis electrocatalytic activity. The results demonstrate that NiSe 2 CE shows the narrower peak-to-peak potential separation,smaller series resistance,charge transfer resistance,the Nernst diffusion impedance,and the larger reduction peak current density and exchange current density,which indicating the excellent electrocatalytic performances of NiSe 2 CE. The reason for this is likely that the pure NiSe 2 nanomaterials with good crystallinity provides the more edge active sites. The adhesive strength between NiSe 2 nanomaterials and FTO glass have been enhanced by the fabrication technique,which is beneficial to facilitate the electron transfer. In addition,the photovoltaic performance of DSCs was carried out by photocurrent-voltage curves. It is found that the DSC based on NiSe 2 CE exhibits the high photovoltaic performance,and achieves the larger energy conversion efficiency of 7.63% than that of the DSC with Pt CE (7.21%). In particular,the fill factor of DSCs is effectively improved from 0.65 to 0.70,due to the small total resistance of NiSe 2 CE. NiSe 2 CE has been successfully designed and synthesized by the electrodeposition-solvothermal-selenization technique. As-prepared NiSe 2 CE exhibits the excellent electrocatalytic performances,resulting in improving the photovoltaic performance of DSCs. Moreover,the fill factor of DSCs with NiSe 2 CE has been effectively improved by the technique.