Impact of the Incorporation of Au Nanoparticles into Polymer/Fullerene Solar Cells

Abstract

The addition of small amounts of dodecylamine-capped Au nanoparticles into the active layer of organic bulk heterojunction solar cells consisting of poly(3-octylthiophene) (P3OT) and C(60) was recently suggested to have a positive impact on device performance due to improved electron transport. This issue was systematically further investigated in the present work. Different strategies to incorporate colloidally prepared Au nanoparticles with a narrow size distribution into organic solar cells with the more common donor/acceptor system consisting of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C(61)-butyric acid methyl ester (PCBM) were pursued. Au nanoparticles were prepared with either P3HT or dodecylamine as ligands. Additionally, efforts were undertaken to incorporate nearly ligand-free Au nanoparticles into the system. Therefore, a procedure was successfully developed to remove the dodecylamine ligand shell by a postpreparative ligand exchange with pyridine, a much smaller molecule that can later partly be removed from solid films by annealing. However, for all types of nanoparticles studied here, the performance of the P3HT/PCBM solar cells was found to decrease with the Au particles as an additive to the active layer, meaning that adding Au nanoparticles is not a suitable strategy in the case of the P3HT/PCBM system. Possible reasons are discussed on the basis of detailed investigations of the structure, photophysics and charge transport in the system.

Uncovering loss mechanisms in silver nanoparticle-blended plasmonic organic solar cells

“…Some functional groups in the ligand may also provide localized states. Topp et al 12 had previously shown that gold nanoparticles encapsulated with different ligands (that is, with dodecylamine, pyridine, and so on) all had detrimental effects on the PCE of P3HT:PCBM OSCs. There is still a lack of understanding on how the capping ligands and particle size affect the net trapping rate.…”

“…Nonetheless, all these issues may be resolvable through a prudent choice of the constituents and careful optimization of the device. From the analysis of our experimental results and careful comparison with the literature reports [8][9][10][11][12][13] , we can identify several key factors/ considerations for the design of hybrid plasmonic OSCs.…”

“…As concluded from charge dynamic measurements, the existence of these foreign entities introduces traps either through the ligands or the NPs. Although optical enhancement is achieved, these NPs can detrimentally affect the exciton 4,6,12 , and polaron lifetimes 13 . Thus, as a practical compromise, the plasmonic absorbers would have to be embedded in the charge transport layers (that is, PEDOT:PSS, ZnO, TiO 2 , and so on), as close as possible to the photoactive layers.…”

“…They should enable uniform dispersion within the embedding layer, eliminating aggregation of the NPs and disruption of the OSC morphology 12,13,38 . When embedding the NPs within the active layer, too thin an outer ligand/shell may result in losses via charge/energy transfer between organic materials and the metallic nanostructure 12 . When embedding the NPs within the charge transport layers, poorly capped NPs could still act as charge trapping sites.…”

“…In the latter approach, NPs coated with organic ligands are typically used to disperse the particles within the organic blends. Despite its simplicity, the findings from this approach are highly controversial as both enhancement [8][9][10][11] and detraction 12,13 in organic photovoltaic (OPV) devices performance have been reported. Physical insight into the fundamental photophysics and charge dynamics in these NP-blended plasmonic OPV cells is urgently required.…”