Ionic Liquid Additive Strategy For Crystallization Regulation And Stable Perovskite Solar Cells

Over the past decade,perovskite solar cells(PVSCs)have achieved unprecedented efficiency breakthroughs.The highest power conversion efficiency(PCE)in the laboratory of PVSCs has reached 25.8%,which is comparable to commercial silicon-based solar cells.Fundamentally,the properties of PVSCs mainly depend on the light absorption capacity,charge separation and extraction of the perovskite layer.However,the excessively fast crystallization process of polycrystalline perovskite films based on the solution method leads to an inevitable number of defects.On the one hand,such defects,as non-radiative recombination center,seriously affect the separation and extraction of electrons and holes,which hinder the improvement of device efficiency.On the other hand,these defects are also the main source of ion migration,dominating the phase segregation and structural disruption within the perovskite.High quality perovskite films not only ensure adequate light absorption and charge transport but also inhibit ion migration at the source.Therefore,the crystallization of perovskite plays a definitive role in the PCE and stability of the whole device.In this paper,the morphology,internal electric field,and ion migration of perovskite films are coordinately regulated through additive engineering to solve the related problems faced by the realization of efficient and stable perovskite solar cells.Multi-functional zwitterionic ionic liquid 3-(1-pyridinio)-1-propanesulfonate(PPS)is used as the active initiator of the reaction between the micro/nano-structure modulator of lead iodide and the solid-liquid interface.Meanwhile,the crystallization quality of perovskite films is effectively regulated by two-step method.PPS has both positively charged pyridine cation and negatively charged sulfonate anion,simultaneously realizing the dual adsorption between inorganic phase and organic phase,which can improve the microscopic adaptability of solid-liquid interface reaction.In addition,the presence of electrostatic interaction can induce the targeted diffusion reaction of organic cation,greatly improving the reaction efficiency of the solid-liquid interface,which is expected to obtain high crystalline quality perovskite films.At the same time,the dipolar interaction of PPS expands the built-in electric field of the perovskite and promotes the separation and transport of electrons and holes.A novel poly(ionic liquids)named poly-1-vinyl-3-propyltrimethoxysilane imidazolium chloride(PImIL-SiO)is first introduced into perovskite to strengthen grain boundaries(GBs)and construct dual-functional barriers against internal ion migration and external moisture erosion for fabricating highly efficient and stable PVSCs.PImIL-SiO containing imidazolium cations and pendant siloxane groups can contribute to the passivation of bulk defects and anchoring of GBs,which effectively hinders ion migration channels,thus reducing perovskite film phase separation and device hysteresis.Besides,the intrinsically hydrophobic PImIL-SiO can automatically form a secondary protective barrier to endow the perovskite film with ultra-high moisture corrosion resistance through the hydrolyzation reaction of siloxane with the permeated moisture.Consequently,the PImIL-SiO modified PVSCs achieve a champion power conversion efficiency(PCE)of 22.46%,companying with excellent thermal and humidity stabilities where the non-encapsulated devices can retain 87%of initial PCE after aging at 85 ℃ for 250 h and > 85% of initial PCE over 1100 h in air with a relative humidity of 50-70%,respectively.