Research On The Performance Of Perovskite Solar Cells Modified With Ionic Liquid Interface

Perovskite solar cells（PSCs）are a new type of photovoltaic cells,whose photoelectric conversion efficiency（PCE）has been rapidly and continuously improved in recent years.The photoelectric conversion efficiency and stability of the device are closely related to the quality of the perovskite absorbing layer（PVSK）and its interface.There are various optimization methods for perovskite absorbent layer and related interface,among which interface modification has achieved particularly outstanding results.However,most of the interface modification materials have a single function,toxic,expensive,and even hard to synthesize,which is not conducive to the standardization selection in actual industrial production.Ionic liquid（ILs）attracts attention due to their good conductivity,strong solvation,and other physical and chemical properties.It has the function of multifunctional modification for perovskite solar cells and is non-toxic and cheap,which is suitable for extensive research and application.In this paper,three ILs,tetramethylammonium hexafluorphosphate（TMAPF₆）,1-ethyl-3-methylimidazole trifluoromesulfonate（EMIMOTF）,and 1-ethyl-3-methylimidazole iodide（EMIMI）,were applied to the interface modification of perovskite solar cells.ILs were used to modify the upper and lower interfaces of perovskite to improve the photoelectric conversion efficiency and device stability of perovskite solar cells.The main contents of the paper are as follows:（1）Solid ionic liquid（ss-IL）TMAPF₆ was introduced into the SnO₂/perovskite interface for interface modification.On the one hand,the modification of TMAPF₆reduced the surface roughness of SnO₂,improved the interface contact between perovskite film and SnO₂,thereby enhancing the surface hydrophobicity of SnO₂,promoted the growth of high-quality and large grain size perovskite film,reduced the interface recombination and the defect state density of the device.Better energy level alignment of SnO₂/perovskite is also induced,leading to better electron extraction.On the other hand,TMAPF₆ improved the interface quality of SnO₂/perovskite by simultaneously passivating the oxygen vacancy on the SnO₂ surface and the MA⁺（I^-）vacancy at the interface under perovskite with TMA⁺and PF₆^-respectively.Finally,the efficiency of the perovskite solar cell modified by the TMAPF₆ interface was increased from 18.62%to 20.92%,and the PCE decreased only 15%of the initial efficiency after the device was stored in the air for 600 h without packaging.（2）IL EMIMOTF was used as a modifier for SnO₂/perovskite interface.Firstly,the OTF^-anions in EMIMOTF interact with SnO₂ through the S=O bond and was distributed on the surface of SnO₂ regularly.Secondly,EMIM⁺cations were mainly distributed on the perovskite side,which generated hydrogen bond interaction with organic cations in perovskite and fixes cations.Meanwhile,N in EMIM⁺formed coordination covalent bonds with undercoordinated Pb²⁺in perovskite.EMIM⁺and OTF^-were distributed regularly at the interface as positive and negative charge centers,respectively,forming an interfacial dipole layer and reducing the energy loss of carriers during interfacial transport.In addition,the modification of EMIMOTF reduced the surface roughness of SnO₂ and improved its hydrophobicity,which contributed to the formation of good interfacial contact and the formation of high-quality perovskite films,inhibited the non-radiative recombination of carriers,and reduces the defect state density of SnO₂ devices.Finally,the maximum PCE of the EMIMOTF-modified perovskite solar cell device was increased from 19.03%to 21.32%of the original device,and the open-circuit voltage of the device was increased from 1.11V to 1.17V.After 55 days of storage in the air,the PCE still maintained more than 80%of the initial efficiency.（3）IL EMIMI was used to modify the surface of perovskite films.On the one hand,hydrogen bond interaction between EMIM+cations and MA⁺effectively reduced the formation of MA vacancy,I^-in EMIMI also effectively passivated I vacancy in perovskite films and reduced surface defects simultaneously.On the other hand,EMIM⁺formed EMIMPbI₃ one-dimensional perovskite with redundant PbI₂ on the surface of perovskite thin film.With excellent humidity stability,EMIMPbI₃ can act as a protective layer on the surface of perovskite thin film,significantly improving the humidity stability of perovskite thin film and battery devices.The final PCE of the EMIMI-modified perovskite solar cell device increased from 18.20%to 19.87%of the original device,and retained 66.72%of its initial PCE after 72 hours of storage in a high-humidity environment.