Ion Activity Inhibition Of Precursor Solution For Efficient And Stable Perovskite Solar Cells

Perovskite solar cells（PSCs）have been widely used and developed rapidly due to their excellent photovoltaic properties,such as high absorption coefficient,long carrier diffusion length and high carrier mobility.Solution processing of PSCs is highly promising for the high-throughput production of cost-effective devices.Over the past 10 years,the photoelectric conversion efficiency of PSCs has increased from3.8%to 25.8%.Although PSCs have achieved great advances in power conversion efficiency,the problem of poor stability of their precursor solutions and devices needs to be solved.The main cause of aging of precursor solution is the highly active iodide ion and formamidine ion in ternary cationic mixed halogenated perovskite system,therefore,inhibition of highly active iodide ion and formamidine ion is an effective way to improve the stability of perovskite ink.However,the current methods for stabilizing precursor solutions are relatively unilateral,which cannot fully solve the aging problem.In order to commercialize PSCs,it is necessary to ensure the stability of production and operation of PSCs.In order to improve the stability of the precursor solution and the device,the reactive inhibition strategy is employed by using additive-induced multiple chemical bond cooperation and dimensional engineering to improve the stability of the precursor solution and the device.The stability of the precursor solution is effectively improved by introducing diethyl（hydroxymethyl）phosphonate（DHP）as a reactive inhibitor.Due to the effectively inhibited reactivity of iodide ion and formamidine ion after adding DHP,deprotonation reaction path of methylammonium cation is cut off,and the production of HI,I₂,I₃^-,MFAI and DMFAI and other by-products in the precursor solution are effectively inhibited.Because vacant orbital of the phosphorus atom in DHP with electron-withdrawing capability would interact with the lone-pair electron in iodide ion,the reactivity of iodide ion can be inhibited and a large number of I₂ and I₃^-and other by-products can be avoided.In addition,the hydrogen bonds can be formed between DHP and formamidine ion to further inhibit the generation of MFAI and DMFAI and other by-products.Hence,the DHP-doped precursor solution exhibits excellent stability under atmospheric conditions.In addition,due to coordination interaction of Pb²⁺with oxygen of P=O in DHP,residual DHP in perovskite films can reduce defects and Pb I₂ to improve film quality and achieve ideal stoichiometry.Due to the multiple chemical bonding,efficient PSCs with improved performance and good repeatability are obtained.In order to further solve the problem of unclear stabilizer residues and passivation persistence in precursor solution,the multi-functional ionic liquid 1-n-Butyl-3-methylimidazolium di-n-butyl phosphate（BMIMBP）is added to the precursor solution,and the long-term stability of the precursor solution and the device is successfully improved.BMIMBP not only can act as a reactive inhibitor to inhibit reactivity of iodide ion and formamidine ion,but also can act as a spacer cation to construct stable low-dimensional perovskite.In this case,the precursor solution doped with BMIMBP and corresponding devices show excellent stability under ambient conditions.In summary,in order to improve the stability of the precursor solution and the device,the reactive inhibition strategy is firstly employed to improve the stability of the precursor solution.Then the reactive inhibition strategy and dimensional engineering are simultaneously employed to improve the stability of the precursor solution and the device.This work offers an efficient method to the commercial feasibility of PSCs.