Preparation And Optimization Of Organic Solar Cells Based On Lanthanum Nickelate

With the depletion of fossil energy and the environmental problems it brings,renewable energy(such as solar energy)has gradually attracted widely attention.Polymer solar cells have the advantages of flexibility,light weight,wet-processed and large-area processing,and have become research topic in the current energy field.Nevertheless,there are still some improvements need to do between commercial silicon-based solar cells and polymer solar cells in energy conversion efficiency and stability.Therefore,further scientific research could help to expand its application.In order to improve the performance of polymer solar cells,this dissertation starts from two perspectives of interfacial engineering and optimization of active materials morphology.In terms of interfacial engineering,a metal oxide,lanthanum nickelate(LaNiO3)with a perovskite structure,was used as a hole transporting layer of polymer solar cell to replace the traditional Poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)(PEDOT:PSS)layer.By comparing the effects of different thicknesses of lanthanum nickelate on the performance of the poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benz o[1,2-b:4,5-b’]dithiophene-co-3-fluorothieno[3,4-b]thiophene-2-carboxylate](PTB7-Th):[6,6]-phenyl-C71-butyric acid methyl ester(PC71BM)based polymer solar cell,the maximum energy conversion efficiency of the device could reach to 9.45%when the thickness is about 8 nm,and its stability is much better than PEDOT:PSS based polymer solar cell.According to the structure characterization,optical testing,and electrical performance of the device,the LaNiO3 layer with the optimized thickness could not only cover the FTO bottom electrode completely,but also decreases the surface roughness of LaNiO3/FTO layer.This method could improve the microscopic morphology of active layer,which determines the photoelectric conversion process in device.Space charge limiting current and transient photovoltage tests have confirmed that holes in PTB7-Th:PC71BM photovoltaic devices with a LaNiO3 of 8 nm have the largest mobility and the smallest bimolecular recombination characteristics,which maximizes the conversion efficiency of the devices.For the optimization of morphology of the active materials,an organic small molecule 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2’,3’-d’]-s-indaceno[1,2-b:5,6-b’]dithiophene(ITIC)was doped into the PBDBT-2F:IT-4F system,thereby preparing a ternary polymer solar cell with an active layer of Poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b’]dithiophene))-alt-(5,5-(1’,3’-di-2-thienyl-5’,7’-bis(2-ethylhexyl)benzo[1’,2’-c:4’,5’-c’]dithiophene-4,8-dione)](PBDB-T-2F):3,9-bis(2-methylene-((3-(1,1-dicyanomethylene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2’,3’-d’]-s-indaceno[1,2-b:5,6-b’]dithiophene(IT-4F):ITIC system.On the one hand,ITIC and IT-4F have similar structures,the phases of the two acceptors could be blended to form an integral phase harmoniously.On the other hand,4 more F-substituted atoms for IT-4F compare to the two terminal groups of ITIC in the molecular structure,which caused a significant difference in the spectral absorption range and intensity of the two molecules and expanded the light absorption capacity of active layer.In this way,it could contribute to the external quantum efficiency of ternary photovoltaic devices.The results show that when the ratio of PBDB-T-2F:IT-4F:ITIC reach to 1:0.8:0.2,the energy conversion eff-iciency of devices of 11.06%was obtained,which is 0.7%higher than the device with PBDB-T-2F:IT-4F(10.36%)and 1.7%higher than the device with PBDB-T-2F:ITIC(9.36%).In summary,this dissertation has shown polymer solar cells with higher conversion efficiency by these two methods,which provide new ideas for the further commercial development of this field.