Investigation On The Photovoltaic Performance Optimization Of Perovskite Solar Cells By Amino-functionalized Pyridine Ionic Liquids

Organic-inorganic hybrid perovskite materials,as a kind of optoelectronic material,is considered to have a bright future and has received extensive attention and research due to its high absorption coefficient,long carrier diffusion length and tunable bandgap.In just a few years,the efficiency of solar cells based on perovskite materials has grown from 3.8%to 25.7%rapidly.And its simplicity and low cost of the process make it possible for large-scale production.However,in the context of future commercialization,how to further address the issue of improving the long-time stability of the device without losing efficiency is the main challenge for perovskite solar cells（PSCs）.In this thesis,amino-functionalized pyridine ionic liquids（ILs）,which are less used in PSCs,were chosen to investigate their effects on the crystalline properties and microscopic morphology of perovskite films and the efficiency and stability of PSCs by rationally designing their molecular structures（including carbon chain length,functional groups,and ions）,and a global optimization strategy for amino-functionalized pyridine ionic liquids was proposed to provide guidance for finding more suitable ILs,as follows:1)In this chapter,three amino-functionalized pyridine ionic liquids with different alkyl chain lengths,including 1-ethylamine hydrobromide-3-methyl pyridine hexafluorophosphate（[EApy]PF₆）,1-propylamine hydrobromide-3-methyl pyridine hexafluorophosphate（[PApy]PF₆）and 1-butylamine hydrobromide-3-methyl pyridine hexafluorophosphate（[BApy]PF₆）,were designed as precursor additives,and their optimization mechanisms were deeply studied.NMR and FTIR spectra show that the amino-functionalized pyridine ionic liquids chemically bonded with the lead and iodine ions in the precursor,which delay the crystallization of perovskite,greatly improve the crystal size of the films and make its morphology continuous and dense.Meanwhile,its strong hydrogen bonding with organic A-site cations can inhibit the decomposition of perovskite and improve the inherent stability of the device.In addition,the strength of chemical bonding is proportional to the alkyl chain length of ILs.Therefore,the power conversion efficiency of the[BApy]PF₆-device increased from 17.23%to 20.36%,and can maintain80%of their initial efficiency after over 600 h without encapsulation.2)In this chapter,through further optimization design,three bilaterally amino-functionalized pyridine ionic liquids with different ions,1-（propylamine hydrobromide）-1-（3-methylamine hydrobromide）pyridine hexafluorophosphate（IL-PF₆）,1-（propylamine hydrobromide）-1-（3-methylamine hydrobromide）pyridine tetrafluoroborate（IL-BF₄）and 1-（propylamine hydrobromide）-1-（3-methylamine hydrobromide）pyridine iodide（IL-I）,are introduced as perovskite precursor additives to explore their effects on performance and stability of device.The experimental results demonstrate that the enhancement of the devices performance mainly depend on the functionalized cations of ILs,while the improvement of the device stability is more related to the fluorinated anions.Among them,the devices based on IL-PF₆ achieve the highest J_sc and FF,but the solvent effect of IL-I itself and excessive I^-compensation of the devices lead to relatively smaller and more hydrophilic perovskite films,which greatly affect the operation stability and long-term stability of the devices.In contrast,the PSCs based on IL-PF₆ achieved a champion power conversion efficiency of 20.45%,while the unencapsulated devices based on IL-PF₆ and IL-BF₄ can maintain 80%of the initial efficiency after being stored in ambient air for 500 h with smaller hysteresis.