The Design And Synthesis Of Functional Cross-Linkable Molecules And Their Application In Perovskite Solar Cells

Perovskite solar cells present a great potential for next-generation solar cells to replace traditional silicon counterparts,because they possess huge advantages in high power conversion efficiency(PCE),low cost and large-area preparation.Recently,with the improvement of the preparation method and the deep investigation of research,the record PCE of perovskite solar cells has reached 25.7%.However,the poor stability limits the commercial application of perovskite solar cells due to the polycrystalline nature of the solution-processed perovskite film.It would produce a large number of defects,which act as the channels for water intrusion and ion migration.Therefore,to improve the efficiency and stability of the devices,this paper focuses on optimizing the quality and stability of perovskite films by developing cross-linkable molecules with passivation and water insulating functions:1.We designed and synthesized a cross-linkable molecule PETA-G by rationally combining the guanidine and tri-acrylate groups,which could simultaneously solve the stability and interface energy levels mismatch problems.The guanidine group with three lone pair electrons enables sufficient bonding between lone pair electrons and undercoordinated Pb2+ of the perovskite grain surface;the tri-acrylate group with three crosslink sites has a moderate crosslinking condition that can spatially crosslink,thus forming a compact network on the perovskite surface.The crosslinked PETA-G(CLPETA-G)can significantly suppress non-radiative recombination and improve the moisture resistance of the perovskite film that even survives when dipped into water,while the charge transport was not influenced.Consequently,the long-term moisture and operational stabilities of the perovskite solar cells based on CL-PETA-G were dramatically increased,and the devices achieved a remarkable PCE as high as 22.6%.2.We designed and synthesized two cross-linkable small molecules,MZ and MTFZ;MZ is mainly composed of oxetane and imidazole units,while the bis(trifluoromethanesulfonimide)(TFSI)was further introduced to MZ to synthesize MTFZ.The two cross-linkable molecules were doped into the lead iodide(PbI2)solution,acting as a scaffold to promote the formation of a porous PbI2 film,which contributed to the fully reaction between FAI and PbI2 as well as the quality of perovskites films.In addition,MZ and MTFZ would in-situ crosslink during the sequential thermal annealing process forming CL-MZ and CL-MTFZ.The multiple functional groups in the two molecules would also efficiently passivate the defects in the perovskite film,which greatly improved the PCEs of CL-MZ(22.7%)and CLMTFZ(23.2%)based-perovskite solar cells,respectively.Finally,these devices also exhibited excellent stability ascribed to the hydrophobic mesh formed by the CL-MZ and CL-MTFZ.