Synthesis Of Perylene-bisimide Based Electron Transport Materials And Their Applications In Perovskite Solar Cells

At present,the efficiency of perovskite solar cell（PSC）has exceeded 25%,which has met the requirements of commercial cell efficiency,but stability is still an important issue facing mass commercial production.Especially,the electron transport layer（ETL）is an important interface layer that extracts and transports electrons from the light absorption layer to the cathode,which plays an important role in the power conversion efficiency and stability of the device.In the inverted planar perovskite solar cells,fullerenes and their derivatives are commonly used electron transport materials.However,their disadvantages include high price,limited energy level adjustment and poor stability,restrict their commercial development.In order to solve these problems,scientists have designed and synthesized many new non-fullerene materials including polymers and small molecules.Particularly,the perylene diimide（PDI）molecules have been widely studied due to their adjustable energy level,easy modification,low price and high electron mobility.This thesis focuses on the design and synthesis of new perylene-bisimide based electron transport materials to improve the efficiency and stability of perovskite solar cells.Inverted perovskite solar cells using these electron transport materials have been fabricated and their photovoltaic properties have been studied.（1）Synthesis of perylene-bisimide fused-ring conjugated small molecules with different side chains and their applications in perovskite solar cellsThree conjugated n-type semiconductors（PDI-OB,PDI-ODB and PDI-OT）from PDI parent with different alkyl side chains were synthesized via bromination of perylene-bisimide and stille coupling with trimethyltin compounds,intramolecular cyclization of perylene-bisimide,and aromatic substituents（4-（（2-ethylhexyl）oxy）phenyl（OB）,4-（octadecyloxy）phenyl（ODB）,5-octylthiophen-2-yl（OT））.The physical,optical,electronic and electrochemical properties of these molecules were characterized.PDI-OB,PDI-ODB and PDI-OT exhibit excellent solubility and thermal stability（with decomposition temperature higher than 400℃）,well matched energy levels with the perovskite,and the high electron mobility(in the order of magnitude of 10^-4cm² V^-1 s^-1).Utilizing these molecules as a single electron transport layer（ETL）,inverted perovskite solar cells with a configuration of ITO/Ni O_x/MAPb Cl_xI_3-x/ETL/Ag were successfully fabricated.Power conversion efficiency（PCE）of5.50%,12.20%and 8.50%were achieved from device using PDI-OB,PDI-ODB and PDI-OT as ETL respectively.In addition,identical structured perovskite device achieved the efficiencies of 15.80%,15.70%and 15.90%respectively when PDI-OB,PDI-ODB and PDI-OT are used as ETL together with C₆₀/BCP,which were comparable to the standard cell（15.40%）using C₆₀/BCP as ETL.These devices exhibited much better stability than that with C₆₀/BCP only device.These devices still maintained 87.97%,93.2%and 98.6%of their initial efficiency after 288 h,while the standard cell using C₆₀/BCP as ETL only maintained 62.30%of the initial efficiency.（2）Synthesis of perylene-bisimide based small molecules by bay substitution and their applications in perovskite solar cellsThree perylene-bisimide based n-type semiconductor materials（PDI-OPh CN,PDI-N and PDI-3N）from PDI parent were synthesized via bromination and amination of perylene-bisimide,and reaction with the nucleophilic group phenoxycyano（OPh CN）or amino unit under base catalysis.The physical,optical,electronic and electrochemical properties of these molecules were characterized.These small molecules have excellent thermal stability with a weakπ-πstacking;they have high electron mobility(in the order of magnitude of 10^-5cm² V^-1 s^-1).However,the LUMO（-3.27～3.52e V）and HOMO（-4.98～-5.27 e V）energy levels do not match with the energy levels of perovskite（CB:-3.80 e V;VB:-5.40 e V）well,which may hinder the effective transport of electrons and the ability to block holes.Utilizing these molecules as a single electron transport layer（ETL）,inverted perovskite solar cells with a configuration of ITO/Ni O_x/MAPb Cl_xI_3-x/ETL/Ag were successfully fabricated.The power conversion efficiency（PCE）of 2.20%,10.20%and 12.70%were achieved from device using PDI-OPh CN,PDI-N and PDI-3N as ETL respectively.