The role of colloidal plasmonic nanostructures in organic solar cells

Abstract

Plasmonic particles can contribute via multiple processes to the light absorption process in solar cells. These particles are commonly introduced into organic solar cells via deposition techniques such as spin-coating or dip-coating. However, such techniques are inherently challenging to achieve homogenous surface coatings as they lack control of inter-particle spacing and particle density on larger areas. Here we introduce interface assisted colloidal self-assembly as a concept for the fabrication of well-defined macroscopic 2-dimensional monolayers of hydrogel encapsulated plasmonic gold nanoparticles. The monolayers showed a pronounced extinction in the visible wavelength range due to localized surface plasmon resonance with excellent optical homogeneity. Moreover this strategy allowed for the investigation of the potential of plasmonic monolayers at different interfaces of P3HT:PCBM based inverted organic solar cells. In general, for monolayers located anywhere underneath the active layer, the solar cell performance decreased due to parasitic absorption. However with thick active layers, where low hole mobility limited the charge transport to the top electrode, the plasmonic monolayer near that electrode spatially redistributed the light and charge generation close to the electrode led to an improved performance. This work systematically highlights the trade-offs that need to be critically considered for designing an efficient plasmonically enhanced organic solar cell.

Plasmonic nanomeshes: their ambivalent role as transparent electrodes in organic solar cells

“…This scattering mode can only exist at the absorption edge of the active layer as the electric field from the particles would be suppressed by a higher attenuation of the polymer 52 . Instead, nanostructured back contacts result in an EQE enhancement pinned to the absorption edge of the polymer, but naturally without transmittance losses 26 53 54 55 56 .…”

“…This is based on their ability to support surface plasmon polaritons (SPP) 20 21 22 . The role of surface plasmons in the performance of thin film solar cells has extensively been studied in the past years 23 24 25 26 27 28 . Surface plasmons have been proposed to trap incident light at the metal/semiconductor interface and thus enhance the light absorption in photovoltaic devices due to an increased interaction time between the light and the active layer and an enhanced field intensity in the device.…”

Mechanotunable Plasmonic Properties of Colloidal Assemblies

“…The resonant field enhancement and subdiffraction electromagnetic energy confinement has led to a variety of applications such as electrochromic smart windows, enhanced oxidation reactions, highly sensitive Raman scattering, energy transport below the diffraction limit, optically active cavities, and nonlinear optical processes . The use of plasmonic back reflectors in photovoltaic devices is of particular interest because they increase the conversion efficiency of inorganic as well as organic solar cells. The intrinsic absorption losses in metallic particles can be used in photothermal therapy, enabling localized heating .…”

Plasmon resonance coupling phenomena in self-assembled colloidal monolayers

“…Since colloidal self‐assembly can be used for monolayer fabrication on cm 2 ‐scale supports, investigation of the optical response by means of far‐field spectroscopy is possible. At the same time such large array dimensions are desired for sensing applications such as SERS and the implementation in photovoltaic devices as light management structures . Such applications require an efficient perfomance screening to elucidate structure‐property relations that help to derive design rules for application‐relevant use of plasmonic monolayers.…”

“…Furthermore, LSPRs can concentrate the light they scatter and absorb into the near‐field volume extending only a few nanometers from the particle surface, reaching field intensities several times higher than the incident driving light . Owed to their unique optical properties plasmonic nanoparticles can serve as light management structures in different photovoltaic devices . Furthermore, the high field strengths can be exploited to enhance weaker optical processes, such as Raman scattering, leading to surface enhanced Raman scattering (SERS) ; or to fundamentally change the emission characteristics of quantum emitters, such as dye molecules and quantum dots, significantly altering the intrinsic lifetime and emission wavelength of fluorophores .…”