Research On Plasmonic-enhanced Organic Solar Cells

In recent years, organic photovoltaic devices（OPVs） have attracted a considerable attention because of advantages of tunable organic material structures, low-cost, large-scale manufacturing process and mechanical flexibility. However, the efficiency of OPV is universally low due to wide band gap of donors, short exciton diffusion length, high exciton dissociation energy, and limited absorption range and ability induced by above factors. One of the most effective approaches is to use localized surface plasmon resonance to enhance the light absorption of these OPVs. Doping metal nanoparticles into OPVs can enhance the local field and the light scattering, thus significantly improving the OPV’s performances via increasing active layer’s absorption.A direct contact of metal nanoparticles with active layer will induce exciton recombination on these nanoparticle’s surfaces and lead to a decline in OPV’s efficiency. Thus in early research, people usually located metal nanoparticles into a carrier extraction layer to avoid exciton recombination on these nanoparticle’s surfaces. With in-depth study, the researchers found that coating the nanoparticles with a shell of dielectric material and locating them into an active layer are beneficial for improving cell’s performances. But there are few reports on the thickness of the dielectric layer so far.In this thesis, we mainly studied the influence of a SiO₂ layer thickness of gold nanorods（Au NRs）@SiO₂ core-shell structures on OPV’s performances based on poly（3-hexylthiophene-2,5-diyl）: fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester（P3HT:PC61BM） and Poly{4,8-bis[（2-ethylhexyl）oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl-alt-3-fluoro-2-[（2-ethylhex yl）carbonyl]thieno[3,4-b]thiophene-4,6-diyl}:fullerene derivative [6,6]-phenyl-C71-butyric acid methyl ester（PTB7:PC71BM） bulk heterojunctions. By changing the thickness of the SiO₂ layer within a large range of 3-38 nm, we found that Au NRs@SiO₂ core-shell structure with an ultra-thin SiO₂ layer is beneficial for realizing a high power conversion efficiency（PCE）, as described below.（1） Note that the Au NRs@Si O₂ were doped into the active layer in the P3HT:PC61BM-based OPVs. The PCE was significantly enhanced from 3.39% in the control OPV without nanoparticles to 4.38% with the nanorods with 3 nm SiO₂ shell layer, with an ehhancement factor of 29.2%. In contrast, the PCE were 3.96% and 3.83% for OPVs with 14 nm and 38 nm SiO₂ shell layers, with the corresponding ehhancement factors of 16.8% and 13.0%.（2） In the devices based on PTB7:PC71BM, the nanorods were doped at the interface of the active layer and the hole extraction layer, the efficiency of the OPV was improved from 7.52% in the control OPV to 9.55% with the nanorods with 3 nm SiO₂ shell layer, with an ehhancement factor of 27.0%, while the PCE were 8.53% and 8.25% for OPVs with 14 nm and 38 nm SiO₂ shell layers, with the corresponding ehhancement factors of 13.4% and 9.7%.