Research On The3D-Ag Nanosheets-enhanced Organic Bulk Heterojunction Solar Cell

Organic solar cells (OSCs) are attractive due to the advantages of low cost, suitablity for large-area fabrication. However, the light absorption depth is-10times longer than the exciton diffusion length in most polymers, which forces a trade off between light absorption and exciton diffusion. The inducement of plasmonics by introducing the metal nanostructures into the organic matrix is a promising approach to resolve this problem. In this thesis,3-D Ag nanosheets (AgNSs) self-assembled on different seed layers via silver mirror reaction are applied to the OSCs. Improved optical absorption and photocurrent are demonstrated due to the increased electric field in the photoactive layer by excited LSPR effect of the3-D AgNSs.The main achievements obtained are summarized as follows:Firstly, we investigated the influence of seeds on the morphology and the density of the silver nanosheets. The study found that the roughness of the seed layer, the density and the degree of lattice matching with the silver are key factors. High degree of lattice matching, low roughness and high density seed layer could induce high density, high-crystallinity and orderly-shape of the silver nanostructure. When gold is the seed layer, the nanosheets with thickness of20nm and height of lOOnm could be obtained.Secondly, the silver nanosheets (AgNSs) prepared via normal silver mirror reaction were used to improve the performance of organic solar cells. AgNSs with a size of about100nm in width and10nm in thickness formed a3-D network on an indium tin oxide (ITO) surface. Organic solar cells with a structure of ITO/AgNSs/PEDOT:PSS/P3HT:PC61BM/LiF/Al exhibited an open circuit voltage of0.60V, short circuit current density (Jsc) of11.16mA/cm2, a fill factor (FF) of53.69%, and power conversion efficiency (PCE) of3.60%. The PCEs of organic solar cells with3-D AgNSs layers were1.29times that of the control device without3-D AgNSs layer. We attributed the improvement of the efficiency to localized surface plasmon resonance (LSPR) induced by the3-D network of AgNSs, which enhanced the light harvest of active layers, increased the probability of exciton generation and dissociation.Thirdly, we study the influence of different thickness gold layer on the performance of the device. The structure is ITO/Au (with and without nanosheets)/PEDOT:PSS/P3HT:PCBM/LiF/Al. After incorporated the gold particles, the device performance is almost unchanged compared with the classical devices, this shows that gold doesn’t prevent the light absorption of the activity layer. The device incorporated0.6nm gold and0.5h nanosheets shown a conversion efficiency of2.29%, which is1.37times of classic devices. The improvement of the efficiency can be attributed to localized surface plasmon resonance (LSPR) induced by the3-D network of AgNSs, which enhanced the light harvest of active layers, increased the probability of exciton generation and dissociation.