Study On Composition Regulation And Defect Passivation Of Ternary Cationic Perovskite Solar Cells

Due to their high absorption coefficient,long diffusion length,low exciton binding energy and high carrier mobility,organic-inorganic hybrid perovskite solar cells have rapidly become a research hotspot in the field of solar cells.In the past decade,their photoelectric conversion efficiency has increased rapidly from 3.8% to 25.5%,which is comparable to that of monocrystalline silicon solar cells.However,there are a lot of defects in the perovskite films prepared by solution method,which are the key factors limiting further improvement of efficiency and causing severe hysteresis.In this paper,the efficiency of perovskite solar cells is improved by adjusting the composition of perovskite light absorbing layer and modifying the additives.The mechanism of alkali metal halide potassium chloride additives on perovskite solar cells is emphatically described,which opens up a new way for the efficiency improvement and hysteresis reduction of perovskite solar cells.The main contents and conclusions of this paper are as follows:(1)Through the composition regulation of perovskite absorption layer and the interface modification of electron transport layer,the standard devices with better performance were prepared.Firstly,the ternary cationic perovskite thin films were prepared by one-step solution method,in which cesium ions were introduced into the perovskite precursor solution.It is found that cesium ion is helpful to improve the crystallinity and light absorption intensity of the film,and enhance the current of the device.When the doping ratio of cesium ion is 5%,the device shows the best performance.On the other hand,in order to relieve the device hysteresis caused by the low electron mobility of titanium dioxide,bis(trifluoromethane)sulfonimide lithium salt was further used to modify titanium dioxide.By optimizing the interface carrier extraction,the hysteresis was effectively reduced,and finally a standard perovskite solar cell with a photoelectric conversion efficiency of 17.4% was obtained.(2)Potassium chloride was used as additive to passivate perovskite thin films effectively.The synergistic effect of potassium ion and chloride ion in improving device performance was discussed.We proved that potassium and chloride ions mainly exist at the grain boundary of perovskite.Potassium ions inhibit the migration of halogen ions through the interaction with halogen,while chloride ions can effectively passivate the halogen vacancy defect sites.Through the effective passivation of defects,the nonradiative recombination of carriers is effectively suppressed,and the lifetime of carriers in perovskite is increased from 28 ns to 182 ns;in addition,the introduction of KCl can regulate the energy band position of perovskite film,thus promoting the interface extraction of carriers.Finally,compared with the standard device(1.087 V),the device added KCl achieves a high open circuit voltage of 1.162 V,and the photoelectric conversion efficiency increases from 17.2% to 18.2%;meanwhile,the hysteresis of the device is effectively inhibited,with a hysteresis factor decreasing from 0.19 to 0.04.Based on the systematic research on optimization,the performance of the ternary cationic perovskite solar cells was effectively improved by adding KCl.In this thesis,the synergistic effects of potassium and chloride ions on passivation defects,carrier transport and device performance are discussed,providing theoretical guidance and a facile strategy for the construction of efficient perovskite solar cells.