Study On The Effect Of Small Molecules On The Performance Of Perovskite Solar Cells

Organic-inorganic metal halide perovskite is a promising photoelectric material with high unique properties of high absorption coefficient,long carrier diffusion length and high carrier mobility.It has exhibited a huge potential in commercialization of photovoltaic field.In the past decades,the power conversion efficiency（PCE）of perovskite solar cells has been dramatically improved from the initial of 3.9%to 25.5%.In this thesis,we try to optimize the fabrication process and use potassium chloride（KCl）and C6A molecules as additive to passivate defects that showing in perovskite films,thus to improve the PCE and long-term stability of PSCs.The main research contents of this thesis are shown as follows:（1）By controlling the experiment conditions,the influence of charge carrier transport layers,perovskite active layer,spin speed and annealing time and temperature on performance of PSCs devices were studied systematically.At the same time,the optimized process for fabrication PSCs were carried out.In addition,the influence of different molecular weight of PTAA on performance of PSCs were studied.Explore the influence of the ratio of organic solvent DMF and DMSO on the crystallization process of perovskite,and to prepare high-quality perovskite crystal films.The preparation process of planar p-i-n PSCs is improved systematically,which provides a foundation for the following work.（2）Study on the influence of KCl additive on performance of MAPbI₃ perovskite solar cells.By introducing K⁺and Cl^-,to realize the dual function of passivation defects in perovskite films surface and promoting the crystal growth of perovskite.Meanwhile,KCl has the advantages of cheap and non-toxic,which is good for commercialization.It is found that K⁺could promote the perovskite to growth into a large crystal and enrich in the grain boundaries and the interfaces between perovskite and charge transport layer to passivate the defects locating at these areas.By optimizing the doping concentration of KCl,the final champion device efficiency is 19.56%,which is improved by 13.6%than that of reference cell（17.22%）.The PCE old encapsulated device can still maintains 57%of the initial value after60 days storage in the air at room temperature with relative humidity of 80%.（3）Effect of C6A additive on performance of MAPbI₃ perovskite solar cells.The special structure and multi-functional groups of the cyclic molecules may realize a multiple passivation of perovskite defects.Through the analysis of our experimental results,we proposed that C=O in C6A may interact with Pb²⁺,to passivates the uncoordinated Pb²⁺defects and reduce the ion migration.It not only reduces the crystallization rate of perovskite,but also generates high quality perovskite films.Moreover,the binding of N-H bond with I inhibits ion migration and increases the electron density on the carbonyl group,which further enhances its passivation effect.In the end,the optimal efficiency of the device passivated with the C6A additive reached 19.67%,and the PCE of the package device retained 94%of its initial value after 500 hours of storage in nitrogen in the glove box.