Research on Fabrication and Performance of Perovskite Solar Cells Based on Zno Materials

Author:Zhang Peng

Supervisor:li shi bin


Degree Year:2019





Benefiting from the unique properties of organic-inorganic hybrid perovskite materials,the power conversion efficiency(PCE)of perovskite solar cells(PSCs)has exceeded 22%after a few years of development and the PSCs become a new research hotspot in the photovoltaic area.The properties of PSCs are directly affected by the quality of perovskite film.Meanwhile,the PSCs usually adopt the layer structure composed of electrodes,electron transport layer(ETL),perovskite film and hole transport layer.As a result,the photo-induced carriers must transfer across these interfaces before they are collected by electrodes.However,due to the existence of interface defects,the carrier recombination also mainly occurs at the interfaces.Therefore,it is important to improve the properties of perovskite film and optimize the interface characteristics of PSCs.In addition,improving the stability and reducing the fabrication cost of PSCs have always been hot and difficult problems.According to the problems mentioned above,in order to obtain low cost,high performance and stable PSCs,we use zinc oxide(ZnO)nanomaterials and compact films to replace the widely used mesoporous titanium oxide(TiO2)film as the ETL.Related researches have been carried out in the following aspects:1.Optimize the fabrication process of perovskite film and improve the quality of perovskite film;2.Modify the interface property and improve the carrier transport efficiency of PSCs;3.Improve the stability of PSCs through interface modification and the use of mixed cations perovskite materials.Firstly,we fabricated the ZnO nanoparticle films and ZnO nanorod films through chemical solution method and hydrothermal method,respectively.The two films were then used as ETL to fabricate PSCs and the effect of ZnO fabrication process on the PSCs performance was systematically studied.For PSCs based on ZnO nanoparticle films,the best PCE of 7.21%was obtained by optimizing the thickness of the ZnO film through adjusting the repetitions of spin coating process.As to ZnO nanorod film,its morphology was adjusted by using different reaction time and solution concentration.The results indicated that the diameter of ZnO nanorods had limited influence on the performance of PSCs,but the PCE of PSCs first increased then declined with the increase of ZnO nanorod length.Finally,PSCs based on ZnO nanorod film achieved the best PCE of 9.65%.The corresponding hydrothermal reaction temperature,reaction time and solution concentration were 90 oC,1 h and 35 mM,respectively.In order to improve the performance of PSCs,ZnO nanorod films were annealed at high temperature and an ultra-thin alumina film was deposited on the surface of ZnO nanorods by atomic layer deposition(ALD)technology for surface modification.The high temperature annealing process effectively removed the chemical residues on the surface of ZnO nanorods,reduced the surface defect concentration and promoted the crystallization of ZnO film.In addition,the introduction of the alumina film passivated the surface defect of ZnO nanorod film.Finally,by optimizing the thickness of alumina film,the PSCs achieved the best PCE of 16.08%and an average PCE of 15.06%.In order to avoid the incomplete reaction of PbI2 during the two-step deposition process,we prepared porous PbI2 films by using mixed solvents.At the same time,ethanol solvent annealing process was used to replace the commonly used thermal annealing process.Porous structure increased the contact area between the PbI2 film and the methylammonium iodide solution,which could promote the reaction between them.On the basis,solvent annealing process further modified the growth process of perovskite grain and significantly improved the quality of perovskite film.As a result,with the help of mesoporous PbI2 film and solvent annealing process,the best PCE of PSCs based on ZnO nanorod films increased to 17.3%.In order to suppress the degradation of PSCs caused by ultraviolet photocatalytic activity of ZnO,we used magnetron sputtering method to fabricate compact ZnO ETL.In addition,an alumina film was used to modify the ZnO film.The magnetron sputtering method improved the crystalline property of ZnO film,avoided chemical residues on ZnO surface and reduced the surface defect concentration of ZnO film,which effectively inhibited the reaction activity of ZnO surface.At the same time,the introduction of alumina layer not only passivated the interface defects,but also inhibitd the photocatalytic reaction between perovskite material and ZnO.At last,PSCs with the best PCE of 17.17%were achieved.After 250 hours of continuous illumination,the PSCs still maintained a PCE of 15.03%,which showed a good stability.Finally,cesium containing triple cation perovskite material was directly deposited on aluminum-doped ZnO(AZO)to prepare the ETL free PSCs and the influence of lattice mismatch on thermal stability of perovskite/AZO film was studied.The results showed that the larger lattice mismatch lead to the accumulation of stress and interface defects in the perovskite film and the deterioration of the crystal quality of perovskite films,which further accelerated the thermal decomposition of perovskite materials on the surface of AZO film.In order to alleviate the thermal degradation process of perovskite film caused by lattice mismatch,barium hydroxide(Ba(OH)2)films were used to modify the AZO surface.The surface modification efficiently improved the thermal stability and crystallization characteristics of perovskite films.By optimizing the thickness of Ba(OH)2film,the best PCE of 18.18%was obtained.