Study On Transparent Electrodes For Large-area Flexible Organic Photovoltaic Devices

Organic solar cells（OSCs）are considered as a promising photovoltaic technology due to their merits of light weight,low cost,good mechanical flexibility,and large-area roll-to-roll solution fabrication.Mechanical flexibility is a significant advantage of OSCs.The development of large-area flexible modules is an important breakthrough for the commercial application of OSCs.In recent years,with the rapid development of non-fullerene active layer materials,the power conversion efficiency（PCE）of small-area rigid OSCs has exceeded 19%.However,due to the lack of high-performance flexible transparent electrodes,the efficiency of large-area（>10 cm²）flexible OSCs is still generally lower than 12%.Therefore,this thesis mainly focuses on the fabrication and performance optimization of high-performance flexible transparent electrodes,and further fabricates large-area flexible OSCs.The main contents are as follows:（1）Develop water transfer printing method to prepare transparent conductive polymer PEDOT:PSS films.Polymer PEDOT:PSS is transparent and electrically conductive,and widely used in the fields of organic electronics and printing electronics.PEDOT:PSS dispersion is an aqueous phase,which makes it difficult to form a continuous film on the super-hydrophobic organic active layer surface.In order to obtain continuous PEDOT:PSS film on organic active layer surface,the strategy of adding surfactant to its aqueous dispersion or treating the organic active layer surface with plasma is usually adopted.However,these will lead to the deterioration of the efficiency of non-fullerene OSCs.In this thesis,water transfer printing method was developed to prepare PEDOT:PSS films,which changed the traditional solid-liquid contact during film fabrication into solid-solid contact under the van der Waals force,and this solved the de-wetting issue of PEDOT:PSS aqueous dispersion on super-hydrophobic organic active layer surface.Finally,based on water transfer printing PEDOT:PSS transparent electrode and PM6:Y6:PC₇₁BM active layer,a flexible organic photovoltaic module with an area of5.3 cm² was fabricated and delivered PCE of 8.6%.（2）Use the developed water transfer printing method to realize the preparation of silver nanowires and PEDOT:PSS composite electrodes（PEDOT:PSS/Ag NWs/c-PSSNa）with better optoelectronic performance,and high-efficiency large-area flexible organic photovoltaic modules were fabricated.Compared with PEDOT:PSS electrode,Ag NWs electrode has excellent optoelectronic performance.However,its high surface roughness easily causes device leakage or short circuit.This thesis reported that a strategy of switching the Ag NWs bottom electrode and the silver（Ag）top electrode to avoid the detrimental effect of the high surface roughness of Ag NWs electrodes.Reduce the thickness of PEDOT:PSS film and composite crosslinked PSSNa film（c-PSSNa）to enhance the optoelectronic and mechanical properties of Ag NWs composite film.Finally,based on water transfer printing Ag NWs composite electrode and PM6:BTP-e C9 active layer,a 21 cm²flexible organic photovoltaic module was fabricated,achieving a PCE of12.3%.（3）Taking thin metal Ag film as the research object,flexible transparent thin Ag electrodes with high optoelectronic performance were achieved through growth surface regulation,and high-efficiency and stable large-area flexible organic photovoltaic modules were fabricated.The molybdenum trioxide（Mo O₃）film was used as the wetting layer of thin Ag electrode.Regulating the morphology of Mo O₃ film can effectively inhibit its island growth,reduce the percolation threshold thickness of Ag film,and significantly improve its optoelectronic performance.Based on thin Ag electrode and organic active layer PM6:BTP-e C9:PC₇₁BM,while optimizing device structure of flexible modules,a1350 cm² flexible organic photovoltaic module with a certified efficiency of 12.10%was fabricated,which is one of the highest PCE at present.In addition,flexible devices based on thin Ag electrodes exhibit excellent light stability and bending stability.