Preparation And Application Of Perylene Imide Cathode Interface Materials In Perovskite Solar Cells

Perovskite Solar Cells(PSCs)have been widely studied due to their advantages of low cost,high efficiency,solution processing,adjustable band gap and so on.The power conerrsion efficiencies(PCEs)of PSCs have exceed 25% by improving materials,optimizing crystal size,interface engineering,additive engineering,and these advantages make PSCs the most likely to be commercialized as a new generation of photovoltaic technologies to replace high-cost silicon-based solar cells.However,there are still many problems in the commercialization of PSCs,such as complex preparation process of control structure devices,low efficiency of inverted structure devices,poor device stability,high synthesis complexity of interface materials,low conductivity,and large thickness sensitivity of CIL.To solve these questions,we design synthetic a variety of interface materials with superior electrochemical properties,simple synthesis process,easy to alcohol solution and processing.The interface materials can efficitive improve the photovoltaic performance of PSCs from improving the efficiency of the device,improving the device stability,reducing synthesis cost of materials,and improving the interface layer thickness sensitivity,interface doping and interficial dipole.Two cathode interface materials(CIMs),named 2PDI-FN and 2PDIT-FN,were designed and synthesized by fluorene and PDI unit,and the effects of molecular structure and dopant N-DMBI on the electrochemical performance of the interface,as well as the effects of the interface materials on the photovoltaic performance and stability of the PSCs were studied.Density functional theory(DFT)calculations show that the insertion of thiophene unit increases the coplanar properties of conjugated skeleton in 2PDIT-FN.The larger intermolecular distance makes the amino functional groups in 2PDIT-FN move freely,and it is easier to induce interface doping and interfacial dipole.As s results,2PDIT-FN are endowed with higher conductivity,higher electron mobility,larger self-doping performance and interinterface dipole interaction,which are completely different from 2PDI-FN.The PCEs of inverted PSCs with 2PDI-FN and 2PDIT-FN as cathode interface layer(CIL)are 17.71 and19.06 %,respectively.The higher efficiency of 2PDIT-FN device is mainly due to its better electrochemical performance.In order to further improve the device efficiency,2PDI-FN and 2PDIT-FN were doped with N-DMBI,and the device efficiency of2PDI-FN(+)and 2PDIT-FN(+)as CIL reached to 18.77 and 20.44%,respectively.The 2PDINT-FN interface material was designed and synthesized by using dimethylamino functional groups and the molecular structure regulation strategy described in the previous chapter.The effects of functional groups and dopants on the electrochemical performance of 2PDINT-FN and the effects of interface materials on the photovoltaic performance of PSCs were studied.Compared with 2PDI-FN and2PDIT-FN,2PDINT-FN has extended conjugated framework,and the dimethyl amino functional group at amide position improves the self-doping performance and interinterface dipole performance of 2PDINT-FN,and greatly reduces the work function of the metal electrode.Through theoretical calculation and electrochemical characterization,it was found that 2PDINT-FN had better electrochemical performance,and more dimethylamino functional groups induced the molecule to produce greater interface doping and interfacial dipole interaction.The PCE of inverted perovskite devices with 2PDINT-FN and 2PDINT-FN(+)as CIL reaches20.03% and 21.85%,which is much higher than that of 2PDI-FN and 2PDIT-FN based devices.PDI-4N cathode interface material was designed and synthesized by one-step method,which has low synthetic complexity and industrial figure of merit,and greatly reduces the cost of synthesis.PDI-2N was also synthesized for contrast.The main difference between PDI-2N and PDI-4N is that the amide position of the former one is an alkyl chain,while the latter one is a dimethyl amino functional group.PDI-2N and PDI-4N show good alcohol-solubility,and PDI-4N has higher conductivity and electron mobility due to strong self-doping properties,and has strong modification effect on metal electrode.Using PDI-4N as cathode interface material,the efficiency of inverted perovskite device is 21.33%,while that of PDI-2N device is only 17.43%.The higher device efficiency of PDI-4N devices is mainly attributed to reduced defect density and charge recombination in devices,resulting in better surface morphology and improved charge transfer and collection at the PCBM/Ag interface.In addition,the two interface materials greatly improve the stability of the device.Two perylene imide oligomers,PDI-D and PDI-T,were designed and synthesized by using asymmetric PDI molecules,and physical and electrochemical properties were improved of PDI-T by adjusting the concentration of quaternary ammonium salt.The concentration of quaternary ammonium salt in PDI-T molecule is higher,so it has higher conductivity,electron mobility and self-doping performance.The effect of PDI-D and PDI-T as cathode interfaces on the photovoltaic performance of inverted perovskite devices is studied.The device efficiency of PDI-D and PDI-T interfaces is 17.13 and 21.06 %,respectively,while that of devices without cathode interfaces is only 11.21%.We found that the device performance at the PDI-T interface is obviously thickness insensitive to the interlayer thickness,and the device efficiency can still exceed 20% even at the PDI-T thickness of 51 nm.In addition,the PDI-T device also showed good stability,with only a 3.3 % efficiency loss after 1032 hours of storage in nitrogen.