Design,Synthesis And Photovoltaic Properties Of Organic Small Molecule Acceptor Materials

The solar cell industry has grown rapidly in recent years,the GaAs solar cells and Crystalline Si cells generally achieving efficiencies of more than 20%.However,the high cost and toxicity of these cells have limited their further development.As a new green renewable energy collection technology,organic solar cells have been widely studied and developed due to their advantages of flexibility,translucence and flexible structure.However,in order to further promote the commercial use of organic solar cells,it is not only necessary to consider the photoelectric conversion efficiency,but also the complexity and cost of their synthesis should be considered.With the continuous development of new receptor materials,the maximum efficiency of organic solar cells has exceeded 17%.However,the types of highly efficient acceptor materials are very limited,and the molecular structures are limited to IDT,IDTT and similar conjugated aromatic ring cores.In this thesis,we focused on developing organic small molecule acceptor materials with high efficiency,low cost and simple synthesis.It is divided into the following three parts:?1?Two novel non-fullerene small molecule acceptor materials bis-BFCP-Bu and tetra-BFCP-Bu were designed and synthesized.We used n-butylated cyanopyridinone as the electron-deficient terminating group,and used 9,9'-bifluorenylidene?9,9'BF?as the core unit.The absorption spectra of the two materials were 350?650 nm and 350?750 nm,respectively.Their optical bandgaps were 1.94 eV and 1.68 eV,respectively.Their HOMO/LUMO energy levels were-5.39/-3.45 eV and-5.53/-3.85 eV,respectively.Their molar extinction coefficients???were 5.23×10⁴ and 8.34×10⁴ M^-1 cm^-1,respectively.It is found that with the increase of the number of electron-deficient terminating groups,the intramolecular charge transfer effect gradually increases,leading to widening and red-shift of the absorption spectrum,which reduces the optical band gap,increases the molar extinction coefficient and regularly changes the molecular energy level.This will be an effective means to improve the photoelectric properties of the receptor materials.Correspondingly,PBDB-Th was used as donor,bis-BFCP-Bu and tetra-36CP-Bu were used as acceptor to prepare organic solar cell devices?ITO/PEDOT:PSS/Active layer/PDINO/Al?,and their optimal PCEs were 1.20%and 1.80%,respectively.?2?To further improve the properties of the material.The bis-BFCP-EH and tetra-27CP-EH were designed and synthesized.Cyanopyridone modified by 2-ethylhexyl was used as the electron-deficient terminating group,and 9,9'-bifluorenylidene?9,9'BF?was used as the core unit.By replacing n-butyl with 2-ethylhexyl,the increased side chain can improve the solubility and miscibility of the materials in the halogenated solvent.On the other hand,the sealing site is changed to 2,2`,7,7`-on the basis of tetra-36CP-Bu,where the steric resistance between the terminal groups and the core unit is large,which may effectively inhibit the undesirable aggregation of molecules caused by the terminal groups.It is found that bis-BFCP-EH and tetra-27CP-EH have good photophysical and thermal stability,and the photoelectric properties of the materials change regularly with the numbers of terminal groups and the change position of seals.PBDB-Th was used as the donor,bis-BFCP-EH and tetra-27CP-EH were used as the acceptors to prepare organic solar cell devices?ITO/PEDOT:PSS/Active layer/PDINO/Al?,and their optimal PCEs were 1.34%and 2.94%,respectively.The results were consistent with the expected.?3?Due to its rigid co-planar structure and large conjugated domain,the ring-fused core molecule has great potential,which is beneficial to improving the intermolecular?-?stacking.In this part,InCP,InIC and InIC-4F are designed and synthesized by using indolocarbazole as the core unit.The three electron-pulling terminal groups are?cyanopyridinone,2-?3-oxo-2,3-dihydro-1H-inden-1-ylidene?malononitrileand2-?5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene??,respectively.The structure-property relationship,photophysical properties and photovoltaic properties of the molecules were investigated.It was found that the absorption spectra of the three materials were 350?700 nm,350?800 nm and 350?880 nm,respectively.Their optical bandgaps were 1.75,1.52 and 1.41eV,respectively.Their HOMO/LUMO energy levels were-5.61/-3.86 eV,-5.70/-4.18 eV and-5.66/-4.25 eV,respectively.Their molar extinction coefficients???were 1.21×10⁵,1.38×10⁵and 1.49×10⁵ M^-1 cm^-1,respectively.The results show that the intramolecular charge transfers effect increases with the enhancement of the electron pulling ability of the terminal group.This induces the molecular absorption spectrum to widen and redshift,the optical band gap to narrow,the molar extinction coefficient to gradually increase,and the molecular energy level to change regularly.The enhanced optical performance is beneficial to improve the photocurrent and reduce the energy loss to achieve higher photoelectric conversion efficiency.When InIC was used as the acceptor and chloronaphthalene was used as the additive,the device efficiency could reach the highest.The PCE after simple solvent annealing was to be 3.20%.