【作者】 邓飞；

【导师】 施德安； 蒋涛；

【作者基本信息】 湖北大学 ， 材料学， 2017， 博士

【摘要】 为了应对全球能源危机,各国已积极投入可再生能源的开发。绿色能源政策的制订与推动将使太阳电池有很大的成长空间。1991年瑞士科学家Michael Gratzel团队提出以二氧化钛(TiO2)纳米结构电极及染料组成光电效率超过7%的染料敏化太阳电池(DSSC),引起了各界对DSSC的研究热潮。随着纳米材料科学的发展,近来年发现量子点的碰撞电离效应能使一个高能量的光子激发出两个甚至多个热电子,得到高于100%的量子产率。量子点的这些特性使得量子点敏化太阳电池(QDSSC)的最高理论效率可达到66%,比单一有机染料敏化电池的理论效率31%高出一倍,可见量子点在敏化电池应用上的潜力。就理论而言,量子点的优点和特性使其具有极大的发展潜力,但目前将量子点敏化太阳电池光电转化效率与传统太阳电池仍然相差甚远。本论文从量子点敏化太阳电池结构与原理出发,重点考虑量子点敏化光阳极的材料性能、制备方法以及界面修饰等几个方面的影响,制备了三维有序的网络结构即反蛋白石结构的二氧化钛(TiO2)多孔膜,采用连续离子吸附法和化学浴沉积法制备了一系列不同量子点敏化和共敏化的光阳极,对TiO2薄膜与量子点间的界面进行了修饰,并对其构建的电池性能进行了研究。首先,利用模板法制备了高度三维有序反蛋白石结构TiO2多孔薄膜并进行了结构形貌表征,用反应离子吸附法与化学浴沉积法制备CdS、CdSe、PbS量子点并实现了多种量子点在反蛋白石结构TiO2多孔薄膜上的原位生长,进一步制备了光阳极并组装了QDSSC。获得了基于三维有序网络结构TiO2的CdS/CdSe量子点敏化太阳电池。该三维有序TiO2薄膜的量子点共敏化太阳电池是一种提高QDSSC效率的有效途径,三维有序的反蛋白石结构TiO2与CdS/CdSe量子点的有力结合充分发挥了分别具有这两种特点的QDSSC的优势,CdS/CdSe构筑阶梯能级促进电子的传导,反蛋白石结构TiO2有效促进量子的沉积并避免TiO2表面易被堵塞的问题。进一步对采用PbS/CdS/CdSe三种量子点共敏化的QDSSC进行了制备与性能研究。三重阶梯能级有助于拓宽吸收光谱,增强对太阳光的吸收量,便于电子在器件内部的扩散与传输,但同时电子的寿命减少,故QDSSC的效率受到制约。其次,我们发现直接将量子点敏化的TiO2纳米晶组装成QDSSC,电池的光电转换效率并不高,着重探讨了界面修饰的方法来提高电池的光电转换效率。首先用烧结法制备了TiO2纳米晶薄膜,用反应离子吸附法与化学浴沉积法制备CdS、CdSe、PbS量子点并实现了多种量子点在TiO2薄膜上的原位生长。在制备光阳极的过程中,我们采用了一种全新的界面修饰方法,将ZnS插入TiO2与量子点的界面间进行了界面修饰。从吸收光谱中可以看到,随着ZnS在TiO2和量子点之间的插入,CdS量子点吸收峰强度和吸收峰的红移愈加明显,这表明CdS量子点沉积量的增加,量子点的粒径也在逐渐增大。这说明在TiO2表面加入ZnS层的修饰可有效促进量子点的生长,提高量子点的沉积量并促进其成核,同样的实验条件下可在光阳极上更有效地制备量子点,提高光阳极的光吸收能力,得到的光电转化效率更高。最后,论文进一步的探讨了在具有反蛋白石的三维有序结构TiO2上进行界面优化。在制备光阳极的过程中,我们同样在反蛋白石TiO2薄膜与量子点的界面插入ZnS修饰层。经过ZnS界面修饰的电池能量转换效率达到3.75%,是未经ZnS修饰的电池效率(2.09%)的1.79倍,电池的填充因子(FF)从0.288增大为0.422。ZnS修饰后,光生电子向光阳极界面缺陷和电解质氧化态的逆向复合减少,从而增加的光吸收能力,促进了光电流的增长。ZnS插入层因促进量子点的生长进而促进了吸收光谱的增强,能够改善电池内部电荷转移电阻和传输电阻,通过TiO2/量子点/电解质接触面的电子转移与传输分析,虽然该界面处的电子寿命有所下降,但总的来说获得了促进电池光电流提升与光电效率提升的效果,是进一步提升基于三维有序TiO2的共敏化量子点太阳电池性能的有效途径。更多还原

【Abstract】 Governments over the world have pitched into the development of renewable energy to deal with energy crisis.The fomulation and promotion of Green Energy Policy has greatly enhanced the development of solar cells.In 1991,Michael Gratzel et.al.firstly proposed dye-sensitized solar cells(DSSCs)composed of nano structured titanium dioxide(TiO2)electrode and dye,which could attain cell efficiency of more than 7%,attracted a stirring of research interest in DSSCs.It is found that two or more hot electrons can be excited by a high-energy photon via impact ionization effect of quantum dots(QD),which yields an over 100%quantum productivity.The characteristics of QDs enable the maximum theoretical efficiency of quantum dot sensitized solar cells(QDSSCs)up to 66%,which is twice as high as that of single organic DSSC of 31%.So QDSSCs have great potential in application.However,the current energy conversion efficiency of QDSSCs is still far below that of the traditional solar cells.Based on the structure and principle of QDSSCs,this research mainly focuses on the effects of materials,structures and interface modification methods on the cell performance.The three-dimensional ordered TiO2 inverse opal films are fabricated.Then a series of photoanodes sensitized by different QDs are prepared by successive ionic layer adsorption and reaction(SILAR)and chemical bath deposition(CBD)methods.The interface between TiO2 film and QDs is modified.Solar cells based on these photoanodes are then assembled and investigated.Firstly,three-dimensional ordered TiO2 inverse opal film was fabricated using template method,and its structure and morphology were characterized.CdS,CdSe and PbS QDs was grown in situ by SILAR and CBD method on TiO2 inverse opal film to form the photoanodes.TiO2 inverse opal based CdS/CdSe co-sensitized solar cells were obtained for the first time by assembling the QDSSCs.The combination of TiO2 inverse opal electrode and cascade-structured CdS/CdSe QDs co-sensitizers has fully exploited their advantages to further improve the performance of QDSSCs:CdS/CdSe build a stepwise band-edge level structure to promote the transferring of electrons,and the deposition of the QDs on top of TiO2 inverse opal effectively prevents the clog of photoanode.The triple stepwise band-edge level structure of PbS/CdS/CdSe co-sensitized solar cells are benefit to broaden the absorption spectrum and harvest more light,as well as facilitate the diffusion and transportation of charge carriers inside the devices.However,the lifetime of electrons is reduced,which will limit the cell.Secondly,in order to improve the energy conversion efficiency of QDSSCs,TiO2 nanocrystalline thin films are prepared via sintering,on which CdS,CdSe and PbS QDs are in situ grown by SILAR and CBD method.When preparing the photoanode,a novel interface modification method is utilized,i.e.ZnS inserting layer is introduced at the interface of TiO2/QD.It can be seen from the absorption spectrum that with the insertion of ZnS between TiO2 and CdS QDs,there is an apparent and red shift of the absorption peak with intensity increase,which indicates the enhanced deposition of CdS QDs and larger grain size.The results show that the modification of ZnS layer on TiO2 surface can effectively promote the growth of QDs,which is benefit for the light harvesting and increasing the photoelectric efficiency.Finally,the thesis discusses the effects of interfacial modification on the photoanode based on three-dimensional ordered TiO2 inverse opal.The energy conversion efficiency of the device modified by the ZnS inserting layer is 3.75%,which is 1.79 times of the non-modified one(2.09%),and the fill factor(FF)of the solar cell increases from 0.288 to 0.422.With the introduction of ZnS inserting layer,the reverse recombination of photogenerated electrons toward the interface defects of photoanode and the oxidation state of the electrolyte is reduced.The light absorption effeciency and the photocurrent axe increased.The inserting of ZnS layer promotes the growth of QDs decreases?the internal charge transfer resistance and transmission resistance inside the solar cells.The analysis of the electron transfer and transmission of the TiO2/QDs/electrolyte interface shows that the electron lifetime at the interface is reduced.However,the overall photocurrent and cell efficiency can be improved and the modification is proved to be an effective way to further enhance the performance of QDs co-sensitized solar cells based on three-dimensional ordered TiO2.更多还原