Performance Enhancement For Polymer Solar Cells

As the continously spreading of the energy crisis and the gradually depletion of traditional fossil energy resources in the world,the people need a green,renewable energy urgently.The direct conversion of solar light into electricity,called photovoltaic technology,is one of the most important approaches to solve the serious energy and environmental problems.Polymer solar cells?PSCs?attract extensive attention due to their ease of fabrication,low cost and flexibility.During the past decade,the performance of PSCs has continuously been improved with power conversion efficiencies?PCEs?over 12%.It is well known that the phase separation and the morphology of the active layer have great influence on the transportation and separation rate of the excitons and the transportation efficiency of the charge carriers.What's more,the interfaces in the device will affect the recombination efficiency of charge carriers.Thus,the device property depends on the phase separation of the active layer and the interfaces in the device.Two-dimensional structure of graphene has shown many execllent optical,electrical and mechanical properties,which has been applied in solar cells as the transparent electrodes,interface layers and electron acceptors.In this dissertation,we blended graphene oxide?GO?into PEDOT:PSS as hole transporting layer,GO functionalized by DDAB as electron acceptor,and fabricating flexible transparent WO₃/Ag/WO₃ electrode in organic solar cells to improve the device performance.Some main conclusions are listed as following:?1?A simple method to modify poly?3,4-ethylenedioxythiophene?:poly?styrenesulfonate??PEDOT:PSS?by directly blending graphene oxide?GO?into PEDOT:PSS to form?PEDOT:PSS?:GO nanocomposites is presents.The transmittance of the?PEDOT:PSS?:GO films exceeds 85%for the wavelengths from 450 to 800 nm.An enhanced conductivity is obtained than that of pristine PEDOT:PSS due to the benzoid-quinoid structure transition of PEDOT:PSS.By applying the obtained?PEDOT:PSS?:GO nanocomposite film as the hole-transporting layer?HTL?in polymer solar cells ITO/HTL/Active-layer/Ca/Al,in which the active layer consists of poly?3-hexylthiophene-2,5-diyl??P3HT?:[6,6]-Phenyl C₆₁ butyric acid methyl ester(PC₆₁BM)or P3HT:indene-C₆₀ bisadduct?ICBA?,we found that the power conversion efficiency of these two OSCs reached to 3.96%and 5.89%,respectively,showing correspondingly enhancement of 14.78%and 9.89%as compared with those of the control devices in which PEDOT:PSS without any modification.?2?By using a simple and non-poisonous"surfactant treatment"method,we prepared graphene oxide?GO?in organic solvents with good dispersibility.As the surfactant molecules,didodecyldimethyla-mmonium bromide?DDAB?was attached onto the GO sheets via ionic interactions.As an acceptor,GO:DDAB was blended into P3HT:PC₆₁BM with different concentrations and then it is applied as the active layer in the PSCs.The PCE of the device increases firstly and then decreases with increasing the concentration of GO:DDAB in the blended active layer.The best PCE of the device ITO/PEDOT:PSS/P3HT:PC₆₁BM:?GO:DDAB?/Al reaches to 3.67%with a concentration of0.5 mg/mL for GO:DDAB.And it reaches to 7.96%for ITO/PEDOT:PSS/PTB7:PC₇₁BM:?GO:DDAB?/Al.Therefore,our experimental data showed that GO:DDAB nanocomposites provides continuous transport pathways and serves as a bridge connecting PC₆₁BM and Al electrode,forming the transported network of electron,balancing between electron and hole transport,as well as to improve the excitons dissociation.?3?We fabricated a kind of flexible and transparent WO₃/Ag/WO₃?WAW?multilayer and used it as electrode in PSCs.By inserting a thin Ag film between two tungsten oxide?WO₃?layers,the two WO₃ layers can act as antireflection films due to the interference effect and the transmittance of the Ag film from both sides was enhanced.Thus W/A/W multilayer can acquire both high transparency and high conductivity?the conductivity comes from the Ag film?.By optimizing the thickness of Ag,WAW shows high average transmittance of 81.4%and low sheet resistance of 19?/.By using of a spin-coated transparent dielectric layer of polyacrylonitrile,the devices can be transferred onto other unconventional substrates like papers,polyethylene glycol terephthalate?PET?and leafs.In this way,transparent and transferrable PSCs were successfully made.