The Investigation Of Electron Transport Layer In Perovskite Solar Cells

With the development of the economy,the problem of environmental pollution has become more and more serious.On the one hand,people advocate reducing the use of traditional energy sources such as oil.On the other hand,they try to seek new renewable and pollution-free energy sources to solve this problem.Solar energy is inexhaustible and it is one of the cleanest energy sources.At present,solar energy is mainly applied to photovoltaic devices such as solar cells,which can generate electricity by the conversion of solar energy.The most commonly used solar cells on the market are silicon-based solar cells,but they face two major problems:one is the high production costs and the other is that the efficiency is dif;ficult to break through.Therefore,it is imperative to seek a new type of solar cell with low production cost,less environmental pollution,and high efficiency conversion.Perovskite-based thin-film solar cell has excellent property and high efficiency conversion which attracted peopled attention quickly after the development of silicon-based solar cells.In less than a decade,the perovskite solar cell has developed very rapidly,and the efficiency has increased from the initial 3.8%to over 23%since the organic-inorganic hybrid perovskite materials are first applied to solar cells by Japanese scientist Miyasaka in 2009.Structurally,the traditional perovskite solar cell consists of conductive glass(FTO/ITO),electron transport layer(ETL),perovskite light absorbing layer,hole transport layer(HTL),and metal electrode(Au/Ag).The ETL plays an important role in transporting electrons and blocking electron hole recombination.The most commonly used ETL is titanium oxide(TiO2),which has strong stability and suitable position of the conduction band,which match the conduction band of perovskite very well.However,there have many defects in the interior and surface of TiO2,and the conductivity of it is not too excellent,which result in degradation of the performance of the perovskite solar cell.Another commonly used ETL is zinc oxide(ZnO),which is more conductive than TiO2,and the position of the conduction band is also suitable to match the perovskite.The decomposition of perovskite will be accelerated when ZnO has a direct contact with perovskite,which induce the poor stability of the device.Therefore,it has become a hot topic to seek other suitable N-type semiconductor materials,or to modify the existing ETL to improve the stability and efficiency of perovskite devices.This paper uses the relative position of the energy band to modify TiO2 and try to combine the ZnO and TiO2 to make the prepared material have both advantages.We all know that TiO2 has two phases,which one is rutile and the other is anatase,so we use the difference in energy band position between the two phases to construct a TiO2 phase junction and explore whether the performance of the device is improved.Then we try to construct a heterojunction ETL of ZnO-TiO2 to investigate whether the performance of the device is affected,and whether the final sample can improve the stability of the device.In summary,this paper mainly includes the following parts:The first part gives a general introduction about the research background,history,components and working principle of perovskite solar cells,and briefly expounds the research work and significanee of this paper.In the second part,the two phases of TiO2 were grown by ALD and TIC14 water bath method respectively.Combined with the UPS test and absorption test,the position of the conduction bands of the two phases were known,and the structures of the two phases with different spatial positions were constructed.As a result,it was found that the device performance was significantly improved compared to the single layer of TiO2.And it is found that the electronic capture and movement speed at the interface is enhanced through characterization.In the third part,ZnO and TiO2 were mixed to form a ZnO-TiO2 heterojunction ETL to solve the problem of device stability when use ZnO as ETL.Through a series of characterizations,the performance of device based on this structure has been greatly improved.In addition,the stability is much improved compared to the original.The fourth part summarizes the conclusions of previous work and outlook the future development of perovskite solar cells.