The Research On The Performances Of Surface Plasmon-enhanced Organic Photovoltaic Devices

Organic photovoltaic devices(OPVs)have attracted the researchers enormous attention owing to their potential advantages of low cost、lightweight、simple fabrication process and mechanical flexibility.However,compared with inorganic solar cells,power conversion efficiency(PCE)of OPVs is very low due to insufficient incident light harvesting for the most of photoactive layers、short exciton diffusion length、low carrier mobilities and mismatched energy level for donor and acceptor.Thus,an increase in light capture is an important approach to efficiently improve the PCE.The surface of metal nanoparticles(NPs)can generate strong local fields,which promotes the absorption of active layers.It has been proved to be an effective way to improve the performances of OPVs.With two decades of research and development,different shapes of NPs,such as,Au(gold)nanopheres,Au nanocubes,Au nanorods and so on,have been widely used into OPVs.Meanwhile,lots of work found that the existence of charge carrier recombination at the surface of the bare NPs that largely increased exciton quenching,resulting in a decline in the performances of OPVs.So,researchers coated the bare NPs with a shell of dielectric material in order to substantially prevent the charge recombination.In this thesis,we first synthesized the Au tetrahedra NPs because they can generate an extremely strong local field based on our calculation result with a finite differential time domain(FDTD)method,whose field intensity is 102 higher than the common sphere and rod shapes.Then,we used an insulated polymer poly(sodium 4-styrenesulfonate)(PSS)to assemble the Au tetrahedra NPs,forming a core-shell structure.The experimental results show that PSS is easy to form a thin shell layer on the surface of the NPs,which can make full use of the local field induced by Au@PSS tetrahedra NPs’ strong localized surface plasmon resonance(LSPR),facilitating light harvesting of the device.Finally,we applied the Au@PSS core-shell tetrahedra NPs into the OPVs with poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester(P3HT:PC61BM)and poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b’]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluoroth Ieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)]:[6,6]-phenyl-C71-butyric acid methyl ester(PTB7-Th:PC71BM)based solar cells,respectively.By optimizing the doping concentration of NPs,the solar cell’s performances can be greatly improved,giving the results as follows.(1)For the devices based on P3HT:PC61BM,Au@2.5 nm PSS tetrahedra NPs were located at the interface of the hole transporting layer and the active layer.The PCE was dramatically enhanced from 2.97% in the control device without NPs to 3.65%,with an enhancement factor of 22.9%.(2)For the devices based on PTB7-Th:PC71BM,Au@2.5nm PSS tetrahedra NPs were also located at the interface of the hole transporting layer and the active layer.The efficiency of device was significantly improved from 8.17% in the control device to 9.53%,with an enhancement factor of 16.65%.The great increase in the PCE is significantly ascribed to the strong LSPR property induced by Au@PSS NPs,which obviously promotes the light absorption of photoactive layer and enhances the maximum exciton generation rate(Gmax).In this thesis,the LSPR effect induced by Au@PSS tetrahedra NPs core-shell structure promotes the improvement of OPVs performances.This method can also be applied to various optoelectronic devices including perovskite solar cells and organic light-emitting diodes for fabricating the high performance devices.