Composite Modification Of Interface Layers In Organic Solar Cells

Organic solar cells（OSCs）possess great application potentials due to their unique properties such as solution-processability,flexibility,semitransparency and light weight.Recently,the power conversion effi ciencies（PCEs）of single-junction devices have exceeded 19%by developing conjugated polymer donors and fused-ring electron acceptors,adjusting morphology of the active layers,ect..An interface layer is often introduced between active layer and electrode to optimize interface contact,affoding efficient charge extraction.Interface layers are necessary for efficient OSCs,playing a vital role in realizing high PCEs.Currectly,the cathode interface layer（CIL）and anode interface layer（AIL）materials have shortcomings,limiting the development of OSCs.For example,the common CILs used in conventional OSCs are mostly organic materials,which have low electrical conductivity,limiting the optimized CIL thickness to 5-15 nm and affording high requirements for film fabrication.Poly（3,4-vinyl dioxythiophene）:polystyrene sulfonate（PEDOT:PSS）is the most used AIL in conventional OSCs.However,it shows low conductivity,non-ideal electron blocking ability and has high cost.In this dissertation,low-cost and efficient CILs and AILs are developed by hybridizing organic/inorganic materials to solve the problems mentioned above.A seried of characterizations are conduced on the synthesized hybrid interface layer materials and mechanisms for performance improvement are studied.Further,their applications in OSCs are explored.By combining the commonly used perylene diimides functionalized with amino oxide（PDINO）and Zn O nanocrystals（NCs）with high electric conductivity,a Zn O NCs/PDINO composite CIL with both high electron mobility and dense morphology is developed by optimizing the fabrication process.PDINO fills the pores of Zn O NCs film,and the resulted Zn O NCs/PDINO OSCs show smaller molecular recombination and more balanced hole-electron transport than single interface devices,affording higher PCEs.The OSCs with the Zn O NCs/PDINO CIL also exhibit good tolerance to the CIL thickness,and the PM6:Y6 and PM6:BTP-e C9 devices can achieve high PCEs of over 15%at the CIL thickness of 70 nm.Further,the Zn O NCs/PDINO devices show better stability than those with sole Zn O NCs or PDINO.The results demonstrate that combining the inorganic interface material with high electron mobility and organic interface material with dense morphology is an effective approach to form thick CILs for the fabrication of efficient OSCs with large-scale solution processed technologies.A facile and low-cost CIL is developed by doping PDINO with zinc acetylacetonate（Zn Acac,ZAA）.The acac^-of ZAA interacts with the N-oxides portion of PDINO,which could enhance its n-doping.In contrast to the pristine PDINO CIL,the PDINO+ZAA CIL exhibits lower electron affinity level and higher conductivity.As a result,OSCs with the PDINO+ZAA CIL deliver higher PCEs and exhibit less efficiency decay with thicker CIL than the OSCs with PDINO CIL.The PDINO+ZAA devices shows less molecular recombination and better charge extraction and transport ability.With 10 nm PDINO+ZAA as the CIL,the typical PM6:BTP-e C9 OSCs can achieve an enhanced avarge PCE of 17.1%.A high PCE of 15.4%can still be maintained with 70 nm CIL.ZAA doping PDINO is a simple and low-cost method to optimize PDINO CIL.It is also revealed that the doping optimization of interface layers is an effective strategy for high performance OSCs.The possibility of doping optimization of PEDOT:PSS with alcohols,tungsten-based materials,cobalt/nickel based compounds and functional carbon dots as additives are explored.The devices based on the amino-functionalized carbon dots（CDs-N）doping PEDOT:PSS AIL show the best performance.CDs-N has the advantages of easy synthesis and large conjugated backbone,and the amine functional groups of CDs-N can interact with the insulating PSS to weaken its shielding effect on PEDOT.PEDOT:PSS+CDs-N exhibits superior conductivity,the PEDOT:PSS+CDs-N devices have smaller molecular recombination,higher exciton dissociation and charge transport than pristine PEDOT:PSS devices,affording higher PCEs.When PM6:Y6 is used as the active layer,the average PCE of PEDOT:PSS+CDs-N devices is 16.5%,which is higher than the PEDOT:PSS devices with 15.4%.This study shows that CDs-N doping is an effective way to optimize the PEDOT:PSS performance.A low-cost AIL was prepared by combining Ni O_x and phosphotungstic acid（PWA）in solution for film deposition.When compared with Ni O_x,Ni O_x:PWA composite AIL shows smoother morphology,which is conducive to forming better interfacial contact with the active layer.In Ni O_x:PWA AIL,some Ni²⁺is oxidized to Ni³⁺by oxidant PWA and the ratio of Ni³⁺/Ni²⁺is higher,resulting high conductivity of AIL,which is more conducive to charge transport.The Ni O_x:PWA devices based on PM6:Y6 exhibits an average PCE of 15.7%,which is slightly higher than the PEDOT:PSS devices.The raw materials of Ni O_x:PWA interface layer are cheap,and the interlayer is prepared by a simple with low-temperature post-treatment.Moreover,the PCE of the devices has good tolerance on the proportion and concentration of Ni O_x and PWA.Ni O_x:PWA is a potential AIL material,which is beneficial for the simple and low-cost manufacture of devices.