Design,Synthesis Of N-type Cathode Interface Materials And Their Applications In Photovoltaic Devices

With the development of society and the increasing human demand for energy,solar energy as a green renewable energy is increasingly explored.Polymer solar cells（PSCs）have attracted more and more attention due to their advantages of light weight,solution processability,flexibility and semi-transparency etc.Recent progress has witnessed the vigorous development of power conversion efficiencies（PCEs）for PSCs,since the successful design of novel donor/acceptor photovoltaic materials and interface materials,as well as the optimization of device engineering.Organic inorganic hybrid perovskite solar cells（PVKSC）are recently emerged as a new type and high-efficiency of photovoltaic devices.As an important part of photovoltaic devices,the cathode interface layers can reduce the work function of metal electrode,promote the transportation and extraction of electrons and protect the active layer.In this paper,we focused on the design of novel cathode interfacial materials,aiming to improve the efficiency,optimize the processability and increase the stability of photovoltaic devices.In the second chapter,we introduced perfluoroalkyl chains（with different length）into polyfluorene-based conjugated polymers and used them as cathode interfacial materials in order to improve the device stability.The results show that polymers with perfluoroalkyl chains showed significantly reduced surface energy and improved hydrophobicity.Unfortunately,devices with these cathode interfacial materials showed unsatisfied efficiencies due to the poor ability of work function modification.The improved hydrophobicity of these cathode interfacial materials triggers us to explore hydrophobic cathode interfacial materials for PVKSCs via optimization on the conjugated backbones and side chains.In the third chapter,we have developed n-type cathode interface materials with perfluoroalkyl chains and tertiary amine side chains,which have been applied to efficient and stable PVKSCs.It was found that the efficiency and stability of PVKSCs can be significantly improved by adjusting the ratio of perfluoroalkyl chain and tertiary amine side chain of the interface materials.The amino side chains in ETMs efficiently improve the interface contact and electron collection of PVSCs.The fluoro side chains endow these polymers with excellent hydrophobic properties,which largely enhance their water-resistance capabilities.ETMs with the increased content of fluoro side chains can substantially improve the water resistance of perovskite layers,with a significant improvement in the stability of PVSCs.Our results indicate that the fluoro-and amino-bifunctionalized strategy is a promising method to design ETMs for high-performance and stable PVKSCs.;In the fourth chapter,a series of narrow-band gap conjugated polymers（PFBP,PBBP,PNBP and PDBP）based on benzodifurandione-centered oligo（p-phenylene vinylene）（BDOPV）unit were prepared by a facile,fast,and low-temperature aldol condensation.The optical absorption,energy levels etc.of these polymers were characterized.When used as acceptor for polymer solar cells,the device performanceswere unsatified due to their low electron mobility.We also explore the doping behaviors of these polymer using 4-（2,3-dihydro-1,3-dimethyl-1H-benzimidazol-2-yl）-N,N-dimethylbenzenamine（N-DMBI）and B（C₆F₅）₃（BCF）as n-type and p-type dopants,respectively.It was found that after the addition of n-type dopant N-DMBIinto these polymers could trigger obvious polaron absorption,indicating that BDOPV-based conjugated polymers are prone to b n-doped..In the fifth chapter,we designed a type of water/alcohol-soluble conjugated polymers with high conductivity as cathode interface materials for polymer solar cells.Based on the previous chapter,a series of novel n-doped conjugated polyelectrolytes（CPEs）with high doping levels and conductivity are designed.These CPEs are synthesized via a facile,metal-free,and high-yield aldol condensation protocol from bis-isatin and bis-oxindole monomers.The designed CPEs possess a n-type electron-deficient and rigid conjugated backbone,resulting in easy charge delocalization,enhanced n-doping behaviors,and high conductivity.The evolution on the counterions of these CPEs further alters their n-doping behaviors,charge transporting properties,and work function tunability,etc.By using these CPEs as cathode interface layers for nonfullerene polymer solar cells（NF-PSCs）,high power conversion efficiencies（PCEs）over 16%can be achieved when PM6:Y6 is used as the active component.Moreover,these CPEs can enable efficient NF-PSCs even if their thicknesses are up to 60 nm,indicating the potential of these CPEs as thickness-insensitive ETMs for the fabrication of large-area NF-PSCs.