Study On Perovskite Crystallization Control And Photovoltaic Device Performance

Organic lead halogen hybrid perovskite is a new type of semiconductor material with excellent photoelectric properties.Its high absorption coefficient,low exciton binding energy,long carrier diffusion length and high defect tolerance make it one of the most ideal light-absorbing materials for the new generation of solar cells.As early as 2009,perovskite material was first used as light capturing medium in solar cells,and achieved an efficiency of 3.81%.Since then,with the continuous optimization of perovskite composition,film preparation process and device structure/interface,the photoelectric conversion efficiency of perovskite solar cells has been rising steadily.At present,according to the latest certification by the International Renewable Energy Laboratory(NREL): a single perovskite solar cell developed by the Ulshan National Institute of Science and Technology has an efficiency of 25.5%.In the development of perovskite solar cells,how to control the crystallization quality of perovskite films is one of the most important problems in the preparation of high-performance photoelectric devices.The high quality perovskite films refer to the polycrystalline films with larger grain size and fewer grain boundaries,which are compact and uniform and have no pinholes.High compactness is the key to prevent short circuit and reduce leakage current.Increasing grain size of perovskite and reducing the grain boundary can effectively reduce the defect density inside the film and suppress the non-radiative recombination of the carriers,thus improving the photoelectric performance of the device.At present,the "one-step method" based on antisolvent is an important method to obtain high-quality perovskite films.The crystallization process is affected by ambient temperature,humidity,precursor composition,antisolvent type,annealing conditions and other factors.Different precursors and anti-solvents can greatly affect the thermodynamics and kinetics of perovskite crystallization process,so they play an important role in regulating the crystallization quality of perovskite.Based on the solution method,this paper focuses on the optimization of perovskite precursor additives and antisolvent,and studies the effects of different solvents on the crystallinity of perovskite films and the properties of final devices.The specific content is mainly divided into the following aspects:In the first part of our work,we demonstrate that dimethoxyethanol(2-ME)can be added as a feasible additive to the perovskite precursor solution to improve the crystal quality of perovskite.The introduction of appropriate amount of 2-ME can effectively reduce the proportion of DMSO in the CH3NH3I-Pb I2-DMSO mesophase,which is due to the strong hydrogen bond interaction between 2-ME and DMSO.After further annealing,the perovskite film was smooth and compact without obvious pinholes.At the same time,the introduction of 2-Me reduces the nucleation density of perovskite,obtaining larger size perovskite grains and reducing the density of grain boundaries.Thanks to the improvement of the morphology of the perovskite films,the bulk defect density of the perovskite films prepared with the 2-ME decreased,and the loss of nonradiative recombination of carriers decreased.The perovskite solar cells optimized by 2-ME have higher energy conversion efficiency,smaller hysteresis and better device stability.In the second part of the work,we studied the effect of anisole as an antisolvent on the quality of perovskite films and the photoelectric performance of the devices.In the experiment,we found that different from the traditional use of toluene,chlorobenzene and other anti-solvents,the use of anisole as anti-solvent to prepare perovskite can obtain dense homogeneous perovskite films with good crystallinity in a very wide time window.This broadened process window effectively improves the yield of the devices.The results of Fourier infrared spectroscopy test show that compared with chlorobenzene,there is a strong bond interaction between anisole and DMSO.Thus the content of DMSO in perovskite intermediate films and the crystallization quality of perovskite films can be regulated more effectively,which provides a relatively controllable technical means for obtaining high quality perovskite films.