Research On Donor Material Design And Device Optimization Of Organic Solar Cells

Organic solar cells(OSCs)have attracted wide attention because of their light-weight,flexibility,adjustable color,and the potential of manufacture large-area devices through roll-to-roll printing technology.As the innovation of photoactive materials,which are composed of donor and acceptor,optimization of the bulk heterojunction morphology and understanding the device physics in given OSCs,the power conversion efficiencies(PCEs)have been rapidly improved.In OSCs,it is an important research direction to study the relationship between the active layer material structure and its photovoltaic performance,and then improve its PCE through structure and device optimization.In this thesis,based on widely used benzo[1,2-b:4,5-b']dithiophene(BDT)unit,we developed a series of conjugated polymer donors in the application of OSCs.The relationship between molecular structures,active layer morphology,and photovoltaic performance is profoundly discussed in the whole thesis.The main research results and conclusions are summarized as below:(1)Increased conjugated backbone twisting to improve carbonylated-functionalized polymer photovoltaic performance.Two conjugated polymers(PBTCO-TT and PBTCO-T),which are the only difference in conjugated backbone with thiophene(T)and thieno[3,2-b]thiophene(TT)units,are synthesized and applied in non-fullerene(NF)polymer solar cells.Both polymers have similar absorption profiles in solutions and films at room temperature,but PBTCO-TT has a stronger temperature dependent aggregation property than that of PBTCO-T in solutions.Cyclic voltammetry and density functional calculations confirm that both polymers have close molecular energy levels.After blending with an acceptor of ITIC,PBTCO-TT:ITIC film shows a significantly big surface roughness and strong aggregation compared to PBTCO-T:ITIC film,which lead to a double difference in final PCEs.For the reasons mentioned above,PBTCO-T:ITIC-based device achieved a higher PCE of 10.40%than PBTCO-TT:ITIC-based device.(2)A Carbonylated terthiophene-based twisted polymer for efficient ternary polymer solar cells.We synthesized a new twisted conjugated polymer(P3TCO-1)with excellent solubilities in common organic solvents at room temperature.Ultraviolet-visible absorption spectra and cyclic voltammetry indicated that P3TCO-1 had a wide optical bandgap of 1.90 eV and deep highest occupied molecular orbital level of-5.39 eV.In binary PSCs,P3TCO-1:ITIC-and P3TCO-1:PC71BM-based device showed a PCE of 10.11%and 6.67%,respectively.When the two acceptors of ITIC and PC71BM were combined,the twisted P3TCO-1-based ternary OSC exhibited a significantly boosted PCE up to 11.41%.More importantly,due to the excellent solubility of the polymer,the photovoltaic device prepared by processing the active layer of the green solvent tetrahydrofuran obtained photovoltaic performance comparable to that of chlorobenzene treatment,in which the PCE of the ternary OSC was 11.07%(3)Design of efficient photovoltaic polymer via introducing intermolecular hydrogen-bonding using amide substituent.We synthesized a new conjugated polymer PBDT-A,because amide groups can form intermolecular hydrogen bonds,the material has strong intermolecular interactions,which has unique properties in optical,electrochemical,and photovoltaic devices.The polymer achieved PCEs of 5.25%and 5.36%in the fullerene(PC71BM)system and the non-fullerene(ITCC)system,respectively.Although the PCEs of the polymer is not too high,this polymer has excellent potential for roll-to-roll large-area printing because of its simple and easy synthesis,and its microstructure and stacking method are less sensitive to rapid processing conditions This result provides a new design idea for the development of OSCs with high efficiency and industrial production.Figure[53]table[28]reference[167]...