Research On Performance Improvement Of Perovskite Solar Cells By Small Molecular Passivators With Imidazole

In recent years,organic-inorganic halide perovskite materials have been widely used in solar cell photodetectors photosensitizer and light-emitting diodes due to their excellent light capture ability and carrier transport performance.As a new generation of photovoltaic technology,perovskite solar cells（PVSCs）have attracted wide attention due to their great potential.Currently,the photovoltaic conversion efficiency（PCE）of the PVSCs has increased from 3.8%to 25.7%currently certified.Although3D PVSCs have achieved excellent photovoltaic properties,long-term stability in wet,thermal and optical environments remains a major obstacle to the commercialization of the PVSCs.Therefore,many methods have been reported for improving the stability and performance of devices,including solvent engineering,ion engineering,additive engineering,interface engineering and other methods.Because perovskite decomposition is usually performed between perovskite and the hole/electron interface transport layer（HTL/ETL）and at perovskite grain boundaries,interface engineering and additive engineering are considered to be among the most effective methods for optimizing the efficiency and stability of PVSCs.Passivation defects and control of perovskite surface potential,the interface and grain boundary modification are more studied.Passivating interface defects and reducing interface non-radiation compound loss are key factors to improve the photovoltaic performance of 3D perovskite solar cells.The formation of LD/3D hybrid perovskite is a promising treatment method,which can improve the stability and efficiency of PVSCs.Therefore,this paper focused on the modification of perovskite films.We first developed a conjugated fluorinated benzimidazole cation（FBIm⁺）,which was inserted between 3D perovskite and HTL to generate two-dimensional（2D）perovskite in situ and improve its performance.Secondly,imidazole derivatives cations（Bn⁺,Pd⁺and Pz⁺）were developed and added into perovskite precursor solution as additives to obtain efficient and stable LD/3D perovskite solar cell devices.Specific research contents are as follows:（1）Imidazolidyl FBIm⁺cations act as the interface modification layer of perovskite,and benzimidazole can be anchored to Pb-I frame to form 2D perovskite.Compared with organic ammonium ion with NH₃⁺as the end,imidazolidazole cations interact with metal halides to form more symmetrical hydrogen bonds,thus reducing the intra and out of plane distortion of perovskite.The 2D crystal structures of（FBIm）₂Pb I₄ and（FBIm）₂Pb Br₄ were obtained by using conjugated fluorinated benzimidazole halides as 2D/3D passivating agents for perovskite.Moreover,the conduction and valence bands of the active layer of perovskite were shifted towards the conduction and valence bands of the hole transport material by converting the counter ions from iodide ions to bromine ions.The improved energy level arrangement can accelerate the hole extraction and transfer at the interface between perovskite and HTL,effectively reduce the non-radiative recombination loss at the interface,and thus improve the battery performance.The results show that the PVSCs using 2D/3D heterojunction engineering has a high open-circuit voltage(V_OC)of 1.17V.In addition,the modified FBIm I and FBIm Br devices show excellent operational stability.After 1300 h aging in an air environment with 25℃,25%relative humidity,the initial performance of the modified FBIm I and FBIm Br devices remains at 86%and 84%,while the control PVSCs maintain only 48%.（2）Using imidazole derivatives cationic benzimidazole pyridine and imidazole pyridine（Bn⁺,Pd⁺and Pz⁺）as additives to prepare efficient and stable perovskite solar cells.By using benzene ring,pyridine and pyrazine to increase the number of N atoms,more lone pair electrons can be generated to interact with the C-N in the nitrogenous adduction of perovskite.C=N has Lewis acid base properties and can passivate uncoordinated Pb²⁺benzimidazole cations,which can induce the preferred orientation growth of 3D perovskite crystals and form low-dimensional（LD）perovskite in 3D perovskite films.In addition,the iodine ions formed by using can compensate for the halide vacancy defects formed in the crystallization process of perovskite and passivate the iodide ion defects.The results showed that the LD/3D PVSCs formed by adding Pz I had a high open-circuit voltage(V_OC)of 1.15 V filling factor（FF）of 76.93%,and a PCE of 21.89%.In addition,the Bn I,Pz I and Pd I modified devices showed excellent operating stability,after 1600 h aging in an air environment with 25℃,25%relative humidity,the initial performance of PVSCs remained above 82%,while that of the control PVSCs was only about 65%.