The Study Of Flexible Electrodes In Organic Solar Cells

Due to advantages like diversified materials,ease of fabrication,low cost and intrinsic flexibility,organic solar cells(OSCs)have great potential in wearable devices,flexible digital products and other industries.The most indispensable component of flexible OSCs is the flexible transparent electrodes,which directly affect the power conversion efficiency(PCE)and mechanical flexibility of the devices.Therefore,in order to obtain highly efficient flexible OSCs,flexible electrodes need to possess high transmittance,good bending durability and decent charge-collecting capability.Currently,the most widely used conductive material,indium tin oxide(ITO),is not an ideal candidate for future flexible electrodes due to its high brittleness.Therefore,it is urgent to develop new flexible electrodes with high transparency,low resistance,and good beding durability.Furthermore,the incident light absorption of OSCs is limited by the light absorption spectrum and the thickness of the active layer,which leads to unsatisfactory device performance.Hence,flexible transparent electrodes with efficient light manipulation structure are highly demanded to enhance the light harvesting of OSCs.To address the mentioned issues,we fabricated flexible transparent electrodes with embedded silver nanowires(AgNWs)via a contact-film-transfer technique and introduced a micro light-manipulating structure into the substrate of electrodes,thus realizing the fabrication of highly efficient flexible organic solar cell devices.This work can be mainly divided into 3 parts:(1)Conventional AgNWs electrodes with AgNWs distributed randomly on top of substrates show problems like high surface undulation and high surface roughness.In this work,we proposed AgNWs elctrodes with a novel structure,which was obtained by embedding silver nanowire network into polyimide(PI)substrate via a contact-film-transfer technique.Owing to this strategy,the fabricated AgNWs elctrodes showed great surface flatness with a low roughness of only 3 nm,which could prevent frequent electric leakage and short circuits in OSCs based on conventional AgNWs electrodes.Also,a ZnO dielectric layer was innovatively deposited on AgNWs networks to avoid melting and aggregation of AgNWs during high-temperature preparation of PI,leading to electrodes with a low square resistance of 25.3 ??-1.The introduced ZnO dielectric layer could intensify the bonding between AgNWs and the substrate material,therefore effectively disperses the tensile stress of electrodes in bending state,which greatly enhances the bending resistance of the AgNWs electrodes.(2)To cover the shortage of OSCs in utilization of incident light,polystyrene(PS)microspheres with a diameter of 1 ?m were selected,through theoretical calculations and simulations,as the light-manipulating medium to enhance modulation of incident light by AgNWs flexible electrodes.As a result,transparent flexible AgNWs electrodes with a high haze of 43%were fabricated,which greatly improved scattering of incident light,thus effectively lenthening optical paths of light in devices.Moreo-ver,the electrodes exhibited good electrical conductivity with a low square resistance of 24.4 ??-1 and high total transmittance of 88.18%without being affected by the introduced PS microspheres.(3)In order to achieve a breakthrough in efficiency of flexible OSCs,we fabricated OSCs with PM6:N3:PC7,BM system as the active layer based on hazy flexible AgNWs electrode with light-manipulating effect.According to results of characterization,the utilization of incident light by OSCs was greatly enhanced,the short-circuit current density(Jsc)and power conversion efficiency were significantly improved to 24.96 mA cm-2 and 16.11%,respectively,which were almost the same as the performance of rigid counterparts based on ITO electrodes,thus effectively shortening the gap between efficiency of flexible and rigid OSCs.Owing to the good bending resistance of electrodes,flexible OSCs retained 86%of their original PCE after 5000 bends with a bending radius of 1 mm,showing great bending durability.To conclude,AgNWs flexible electrodes fabricated in this work show properties like easy fabrication and superior performance,which can effectively improve the device efficiency and bending durability of flexible OSCs,thus benefiting commercial development of flexible solar cells.In addition,the design and preparation strategy of the flexible transparent electrodes provides new ideas for designing flexible electrodes in optoelectronic devices such as flexible photodetectors and flexible light emitting diodes.