| The microscopic morphology of the active layer in the bulk heterojunction organic solar cell is one of the important factors affecting the photoelectric conversion efficiency.In this dissertation,we mainly use a novel thick-film conjugated polymer material poly[(5.6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3'"-di(2-Octyldodecyl)2.2';5',2";5",2'"-quaterthiophen-5,5'"-diyl)](PffB'T4T-20D)is an electron donor material,the small molecule of fullerene derived[6,6]-phenyl-C71-butyric acid methyl ester(PC71BM)is an electron acceptor material for preparing an organic solar cell device.The use of different solvent additives regulates the stacking orientation and orderly crystallinity of the polymer molecules in the donor layer in the active layer,and improves the photoelectric conversion efficiency of the prepared device by the constant control and optimization of the active layer morphology.First,we studied the microscopic morphology of the active layer of PftBT4T-20D:PC71BM with different additives,1,8-diiodooctane(DIO)and chloronaphthalene(CN).and the crystalline properties of the internal polymer molecules and the acceptor small molecules.Due to the difference in boiling point of the two additives,the difference in polarity,and the solubility of the acceptor materials,there are some differences in the optimization of the thin film morphology.It has been found that when there is no additive optimization,the phase separation of the donor and acceptor in the active layer is not good,and some larger size of the aggregated region appears.When the additive DIO which only dissolves PC71BM is added,the phase separation of the donor and acceptor materials in the active layer is optimized,but the surface roughness of the active layer is increased compared to the additive-free optimization.When adding the additive CN which has certain solubility to the donor PffBT4T-20D polymer material and the acceptor PC71BM small molecule material,the surface morphology becomes fibrous and uniform compared with the additive-free surface roughness.Grazing incidence wide-angle X-ray diffraction(GIWAXS)results show that the two types of additives.DIO and CN.have different guiding effects on the crystallographic properties of polymer molecules in the active layer.DIO can promote the orderly packing and crystallization of ?-? bonds of polymer molecules in a direction parallel to the substrate of the face-on direction,but the crystallization of the lamellar is weakened.However.CN has the opposite guiding effect on the crystallization of polymer molecules in the face-on direction,which promotes the orderly packing and crystallization of lamellars.but weakens the crystallization of ?-?bonds.These results indicate that the additives DIO and CN with different properties have a certain degree of optimization on the microscopic morphology of the active layer,and can promote the phase separation between the donor material and the acceptor material.thereby improving the performance of the battery device.After optimization with additive CN,the photoelectric conversion efficiency of the device reached 10.25%,the short-circuit current reached 17.752 mA/cm2,and the fill factor was 73.1%.The photoelectric conversion efficiency of the device after optimization of DIO was 8.91%,and the short-circuit current was 16.785 mA/cm2,the fill factor is 66.4%.The two types of additives have different guiding effects on the packing orientation and ordered crystallinity of the polymer molecules in the active layer,which results in different properties of the prepared devices.In order to promote the orderly accumulation of lamellars and ?-? bonds of polymer molecules in the direction parallel to the substrate face-on.to further optimize the morphology of the active layer and improve the performance of organic solar cell devices,we have used double additives.The strategy was to optimize the active layer and the dual additives were selected for diphenyl ether(DPE)and chloronaphthalene(CN).The results of GIWAXS indicate that the additive DPE can promote the orderly crystallization of the polymer molecule PffBT4T-20 in the direction-parallel direction of the substrate,while the additive CN enhances the ordered crystallization of the lamellar.When the additives DPE and CN are simultaneously added to the active layer,the polymer PffBT4T-20D molecules have a certain increase in the ?-? bond accumulation crystal and the accumulation and crystallization of the lamellar in the face-on direction.At the same time,AFM and TEM results show that the microstructure of the active layer after optimization of the double additive is not significantly different from the single additive.After optimizing the use of dual-additives DPE and CN,the photoelectric conversion efficiency of the device was improved to 10.93%,and the efficiency was increased by 8.9%and 4.09%compared with the single-additive DPE(10.03%)and CN(10.50%)optimized devices.This shows that the dual additive strategy not only improves the micro-morphology of the active layer,but also plays a synergistic role in the stack orientation and orderly crystallization of the polymer molecules,which in turn improves the photoelectric conversion efficiency of the device.All high-performance organic solar cell devices currently reported are based on halogenated solvents that pose a serious hazard to the atmospheric environment and human health.The less toxic non-halogenated solvents can not be applied to the device preparation process because of their low solubility in conjugated polymers and small molecules and poor film formation quality.In order to improve the poor film formation quality of non-halogenated solvent active layers,we have found an excellent non-halogenated additive 1-methylnaphthalene(Me)to optimize the non-halogenated main solvent o-xylene(o-XY)prepared active layer PffBT4T-20D:PC71BM system device.The optimized photoelectric conversion efficiency was as high as 10.13%,while the photoelectric conversion efficiency of the device prepared with a single o-XY main solvent was only 1.83%.At the same time,we also compared the performance of the device prepared from the traditional halogenated solvent CB and the halogenated additive DIO under the same conditions,and its photoelectric conversion efficiency was 8.18%.Comparative analysis found that the combination of o-XY+Me to produce high-performance devices is due to the great changes in the morphology of the active layer,resulting in a more slender,uniform phase separation,which has an important contribution to the improvement of short-circuit current.At the same time,using GIWAXS to explore the inside of the active layer,it was found that the polymer molecules prepared by the combination of the non-halogenated solvent o-XY+Me have very high crystallinity and ?-? bond crystallinity in the direction parallel to the substrate.Studies have also found that devices prepared from a combination of' non-halogenated solvents o-XY+Me containing only hydrocarbon elements have better stability than active layers and devices prepared by conventional halogenated solvent CB+DIO combinations. |
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