离子液体电沉积铜铟镓硒薄膜及性能研究

发布时间：2018-09-05 13:24

【摘要】：Cu_(1.00)In_(1-x)Ga_xSe_(2.00)(CIGS)薄膜太阳能电池被认为是具有广阔应用前景的半导体薄膜电池之一,其中CIGS光吸收层是影响薄膜太阳能电池性能的关键材料之一。电沉积方法制备CIGS薄膜具有操作方便、设备简单、可控连续生产等优点。离子液体具有热力学性能稳定、电化学窗口宽等优点,作为电沉积CIGS薄膜的电解液更容易得到组成稳定的CIGS沉积层。因此,研究开发新型离子液体电沉积CIGS薄膜工艺具有非常重要的理论与实际意义。本文研究了离子液体中电沉积CIGS薄膜的工艺及所制备的薄膜的半导体性能,在此基础上明确了离子液体电沉积多元金属的沉积机制及CIGS电沉积行为。根据Cu、In、Ga、Se的特点及离子液体的性质,筛选出1-丁基-3-甲基咪唑三氟甲磺酸盐([BMIm][TfO])离子液体作为电沉积CIGS薄膜的电解液,采用恒电势方法进行电沉积,通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)、电感耦合等离子体发射光谱(ICP)、X射线衍射(XRD)和拉曼光谱(Raman)对电沉积所得CIGS薄膜的形貌、组成和结构进行表征。研究发现,获得的CIGS薄膜均匀致密、表面存在大量的菜花样团簇状结构,组成为Cu_(1.00)In_(0.83)Ga_(0.23)Se_(1.64),且主要表现为沿(112)晶面择优生长的黄铜矿结构的结晶模式,其晶格间距为0.328nm。采用紫外-可见光谱(UV-Vis)和霍尔效应(Hall Effect)测试研究了得到的CIGS薄膜的半导体性能,研究发现恒电势电沉积所得的CIGS薄膜为p型半导体,其禁带宽度为Eg=1.55 eV、载流子浓度为2.74×10~(20) cm~(-3)、霍尔系数为2.28×10~(-2) cm~3·C~(-1)。采用单一离子液体作为电解质时存在电解液的粘度相对较大且电导率较低的缺陷,为此开展了共溶剂体系的研究。依据加入不同种类共溶剂的离子液体[BMIm][TfO]-醇混合体系电解液的性质,筛选出体积分数为30 Vol%的丙醇作为混合体系的共溶剂。选用离子液体[BMIm][TfO]-30 Vol%丙醇混合体系作为电沉积CIGS薄膜的电解液,通过SEM、TEM、ICP、XRD、Raman、UV-Vis和Hall Effect对恒电势电沉积所得的CIGS薄膜的形貌、组成、结构和半导体性能进行研究。研究发现,恒电势电沉积所得的CIGS薄膜表面均匀、致密,组成为Cu_(1.00)In_(0.75)Ga_(0.10)Se_(1.72),呈黄铜矿结晶模式且晶化程度较离子液体[BMIm][TfO]体系恒电势电沉积得到的CIGS薄膜更好、对应(112)晶面的生长更有序,晶格间距为0.340nm。恒电势电沉积得到的CIGS薄膜为p型半导体,其禁带宽度为Eg=1.48 eV、载流子浓度为6.37×1019 cm~(-3)、霍尔系数为9.81×10~(-2) cm~3·C~(-1)。相较于离子液体体系电沉积得到的CIGS薄膜的载流子浓度,离子液体[BMIm][TfO]-30 Vol%丙醇混合体系电沉积所得的CIGS薄膜的载流子浓度变小。恒电势电沉积所得的CIGS薄膜存在大量团簇状结构,即均匀性存在较大的问题,为此开展了脉冲电沉积研究。研究了峰值电流密度、占空比和频率这三个独立变化的参数对电沉积所得的CIGS薄膜的形貌、组成、结构和半导体性能的影响,筛选出峰值电流密度为2 mA·cm~(-2)、占空比为50%、频率为2 kHz作为脉冲电沉积工艺参数。采用脉冲方法进行电沉积,选用[BMIm][TfO]-30 Vol%丙醇混合体系作为电沉积CIGS薄膜的电解液,综合测试结果发现脉冲电沉积所得的CIGS薄膜的表面均匀性得到改善、晶粒度较小,沉积层组成为Cu_(1.00)In_(0.51)Ga_(0.10)Se_(2.04),为p型半导体的黄铜矿结构化合物,(112)晶面的晶格间距为0.328nm。其禁带宽度为Eg=1.35 eV,载流子浓度和霍尔系数分别为1.64×1022 cm~(-3)和3.81×10~(-4) cm~3·C~(-1)。由于四元体系的共沉积机制较为复杂且关于离子液体中共沉积Cu、In、Ga、Se四元合金机理的研究不明确,为此开展了CIGS的电化学行为和电结晶机理的研究。通过循环伏安曲线并结合不同阶跃电势下的电流~时间(I~t)曲线对CIGS的共沉积机理进行了初步研究。分别对一元、二元和多元离子液体[BMIm][TfO]体系进行循环伏安曲线的研究,发现在电沉积CIGS薄膜的过程中,Cu2+最先还原,然后在Cu上电沉积Se,最后在Se上发生In和Ga的沉积。针对离子液体[BMIm][TfO]体系和离子液体[BMIm][TfO]-30 Vol%丙醇混合体系中CIGS的电结晶过程进行研究,发现在离子液体[BMIm][TfO]体系中的电结晶过程受扩散控制,符合三维瞬时成核的生长机制,在离子液体[BMIm][TfO]-30 Vol%丙醇混合体系中的电结晶过程受扩散控制,随着沉积电势的负移,由三维连续成核变为瞬时成核的生长机制。
[Abstract]:Cu_ (1.00) In_ (1-x) Ga_xSe_ (2.00) (CIGS) thin film solar cells are considered as one of the most promising thin film semiconductor cells. Among them, CIGS optical absorption layer is one of the key materials affecting the performance of thin film solar cells. As the electrolyte of electrodepositing CIGS thin films, it is easier to obtain stable CIGS deposits. Therefore, it is of great theoretical and practical significance to develop a new process of electrodepositing CIGS thin films by ionic liquids. The deposition mechanism and CIGS electrodeposition behavior of the multimetal films prepared by ionic liquids electrodeposition were clarified. According to the characteristics of Cu, In, Ga, Se and the properties of ionic liquids, 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIm][TfO]) ionic liquids were selected as electrodeposited CIGS films. The morphology, composition and structure of CIGS thin films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), inductively coupled plasma emission spectroscopy (ICP), X-ray diffraction (XRD) and Raman spectroscopy. There are a lot of cauliflower-like clusters on the surface, which are composed of Cu_ (1.00) In_ (0.83) Ga_ (0.23) Se_ (1.64) and mainly show the chalcopyrite structure growing along the (112) crystal plane. The lattice spacing is 0.328 nm. The CIGS thin films were measured by UV-Vis and Hall Effect. Semiconductor properties were studied. It was found that the C IGS thin films deposited by constant potential electrodeposition were p-type semiconductors with a gap of Eg=1.55 eV, a carrier concentration of 2.74 (20) cm-3 and a Hall coefficient of 2.28 (-2) cm-3 (-1). Based on the properties of the ionic liquid [BMIm] [TfO]-alcohol mixed system with different kinds of cosolvents, 30 Vol% propanol was selected as the cosolvent of the mixed system. SEM, TEM, ICP, XRD, Raman, UV-Vis and Hall Effect were used to study the morphology, composition, structure and semiconductor properties of CIGS films deposited by constant potential electrodeposition. CIGS thin films prepared by constant potential electrodeposition of ionic liquids [BMIm] [TfO] system are better than those prepared by constant potential electrodeposition. The growth of corresponding (112) crystal faces is more orderly and the lattice spacing is 0.340 nm. Compared with the carrier concentration of CIGS thin films deposited in ionic liquid system, the carrier concentration of CIGS thin films deposited in ionic liquid [BMIm] [TfO]-30 Vol% propanol mixed system decreases. The effects of peak current density, duty cycle and frequency on the morphology, composition, structure and semiconductor properties of the deposited CIGS thin films were studied. The peak current density of 2 mA (-2), duty cycle of 50% and frequency of 2 kHz were selected as pulse electrodeposition parameters. The surface homogeneity of CIGS thin films deposited by pulse electrodeposition was improved and the grain size was smaller. The deposited layer was composed of Cu_ (1.00) In_ (0.51) Ga_ (0.10) Se_ (2.04), which was a chalcopyrite structure of p-type semiconductor. The lattice spacing of (112) faces is 0.328 nm. The forbidden band width is Eg=1.35 eV. The carrier concentration and Hall coefficient are 1.64 *1022 cm-3 and 3.81 *10-4 cm-3.C-1, respectively. The electrochemical behavior and electrocrystallization mechanism of CIGS were studied. The co-deposition mechanism of CIGS was preliminarily studied by cyclic voltammetry curves and current-time (I~t) curves at different step potentials. The cyclic voltammetry curves of monobasic, binary and multicomponent ionic liquids [BMIm] [TfO] systems were studied respectively. The electrocrystallization of CIGS in ionic liquid [BMIm] [TfO] system and ionic liquid [BMIm] [TfO] - 30 Vol% propanol system was studied. It was found that the electrocrystallization process in ionic liquid [BMIm] [TfO] system was controlled by diffusion. In accordance with the growth mechanism of three-dimensional instantaneous nucleation, the electrocrystallization process in ionic liquid [BMIm] [TfO]-30 Vol% propanol mixtures is controlled by diffusion. With the negative shift of deposition potential, the three-dimensional continuous nucleation becomes the growth mechanism of instantaneous nucleation.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ153;TB383.2

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