Research On Improving The Performance Of Organic Photovoltaic Devices Using Silver Nanoparticles

Organic photovoltaic (OPV) devices have attracted much interest due to their advantagesof low cost, easily fabrication and mechanical flexibility, which give a promise for industryproduction. However, the low extinction coefficient and low charge mobilities of organicmaterials decrease the performance of OPV devices. So solar-cell design andmaterials-synthesis considerations are strongly dictated by these opposing requirements foroptical absorption thickness (100nm) and carrier collection length (10nm). Recent years,various approaches have been investigated for enhancing the absorbance coefficient of OPV.A promising way to enhance the absorption of OPV is the use of noble metal nanostructuresthat support the surface plasmon.In this thesis, silver nanoparticles (AgNPs) were synthesized via the chemical method,and then were introduced into the OPV device structures. The effects on the solar harvestingand the power conversion efficiency (PCE) improving were investigated by adding AgNPswith different density into different location inside the OPV structure.(I) Well-dispersed and high-purity AgNPs were synthesized with the method ofLiquid-Solid-Solution method. The average diameter of AgNPs is about20nm. Resonanceabsorbance peaks are about425nm in solution and472nm on substrate because of thedielectric constant variation. The peak value can also be enhanced by spin coating layer bylayer to increase the density of AgNPs on the substrate.(II) The mechanism of absorbance enhancement and performance improvement wasinvestigated thoroughly, AgNPs were introduced into OPVs and three kinds of optimizedstructure were fabricated,(a) devices with AgNPs in front of active layer,(b) devices withAgNPs behind active layer,(c)devices with AgNPs inside active layer.By evaluate the optical and photoelectrical properties of these OPVs, we conclude thatthere are four main factors must be considered while studying how the AgNPs affect theperformance.(a) Whether the metal nanostructures cause the light scattering or SPR effect?(b)Whether the metal nanostructures decrease the absorbance of solar-active layer because ofsignificant absorption shadow?(c) Whether the metal nanostructures influenced the chargetransfer process?(d) How does the additive of AgNPs affect the interface potential barriersand interface contacts? So fully considered these factors, we get the highest JSCof10.84mA/cm2, having a promotion of17.44%comparing to control device; while the highest PCEwe obtained is3.98%, having a great promotion of23.60%.