A Study On The Crystal Growth Kinetics Of Perovskite In Mesoscopic Confinement

In recent years,the development of perovskite solar cells in new photovoltaic devices has been particularly rapid with a certified power conversion efficiency（PCE）increasing from 14.1%to 25.5%.This is mainly due to the excellent photoelectric properties of perovskite materials,such as high absorption coefficient,long carrier transmission length,adjustable band gap and high defect tolerance.Among many perovskite solar cell structures,we focus on printable mesoscopic perovskite solar cell without hole transport materials.The inorganic framework of this device can be prepared by simple screen-printing technology,which is simple and easy for industrialized production.In the previous work,we found that additive engineering is one of the simplest and most effective methods to improve the PCE of printable mesoscopic perovskite solar cells.However,still at present,the trial-and-error method is mainly used to find additives to optimize the perovskite,which lacks theoretical basis.This thesis studies the crystallization kinetics process of perovskite under mesoporous confinement conditions.Using synchrotron radiation X-ray diffraction technology,it is proposed to construct a crystallization model to provide theoretical guidance for further improving the performance of printable mesoscopic perovskite solar cells in the future.The main contents include:（1）The application of synchrotron radiation X-ray diffraction technology in printable mesoscopic perovskite solar cells was preliminarily explored using the most classic 5-aminovalerate hydroiodide（5-AVAI）additive as the research object.We find that 5-AVAI additive promotes the formation of randomly oriented dispersed crystallites and inhibits the generation of large crystal grains.In the process of crystallization kinetics research,it is found that 5-AVAI can increase the colloidal size of the precursor solution,accelerate the nucleation of the perovskite,promote the transition from the mesophase to the perovskite phase,and delay the growth of perovskite crystals.In addition,5-AVAI can passivate the defects of the perovskite and enhance the crystallinity of the crystal,thereby greatly improving the efficiency and stability of the device.（2）1-ethylpyridinium chloride（1-EC）ionic liquid was introduced into the perovskite precursor solution.The results show that 1-EC ionic liquid can passivate perovskite crystal defects and promote carrier transport,and this effect is equally effective in other solvents and perovskite components.The synchrotron X-ray diffraction technique was used to characterize the effect of 1-EC ionic liquid on the crystallization kinetics of perovskite under restricted conditions.The results indicate that 1-EC ionic liquids can cause rapid nucleation and slow crystal growth of perovskite.In addition,MAPb I₃ precursor with 1-EC ionic liquids will form a highly oriented mesophase,which helps to generate high-quality out-of-plane perovskite crystals.Therefore,the PCE of the device has increased from 9.19%to15.14%.（3）The effect of chlorine-containing additives on the crystallization process of perovskite was systematically studied.Three chlorine-containing additives,including lead chloride,methylamine chloride and acetamidine hydrochloride,were used as the research pair.The results showed that chlorine is helpful to the filling and growth of perovskite in the mesopores and plays a key role in the passivating defects in the perovskite.In exploring the effect of chlorine on the crystallization kinetics of perovskite under restricted conditions,the study found that the presence of chlorine-containing additives would cause the instability of the mesophase MA₂Pb₃I₈·2DMSO and promote the transition from the mesophase to the perovskite phase.In addition,chlorine can also promote the oriented growth of perovskite under mesoporous confinement conditions,thereby improving the PCE of the device.