| 1. |
- Gillett, Alexander J., et al.
(författare)
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The role of charge recombination to triplet excitons in organic solar cells
- 2021
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Ingår i: Nature. - : NATURE PORTFOLIO. - 0028-0836 .- 1476-4687. ; 597:7878, s. 666-
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Tidskriftsartikel (refereegranskat)abstract
- The use of non-fullerene acceptors (NFAs) in organic solar cells has led to power conversion efficiencies as high as 18%(1). However, organic solar cells are still less efficient than inorganic solar cells, which typically have power conversion efficiencies of more than 20%(2). A key reason for this difference is that organic solar cells have low open-circuit voltages relative to their optical bandgaps(3), owing to non-radiative recombination(4). For organic solar cells to compete with inorganic solar cells in terms of efficiency, non-radiative loss pathways must be identified and suppressed. Here we show that in most organic solar cells that use NFAs, the majority of charge recombination under open-circuit conditions proceeds via the formation of non-emissive NFA triplet excitons; in the benchmark PM6:Y6 blend(5), this fraction reaches 90%, reducing the open-circuit voltage by 60 mV. We prevent recombination via this non-radiative channel by engineering substantial hybridization between the NFA triplet excitons and the spin-triplet charge-transfer excitons. Modelling suggests that the rate of back charge transfer from spin-triplet charge-transfer excitons to molecular triplet excitons may be reduced by an order of magnitude, enabling re-dissociation of the spin-triplet charge-transfer exciton. We demonstrate NFA systems in which the formation of triplet excitons is suppressed. This work thus provides a design pathway for organic solar cells with power conversion efficiencies of 20% or more. A substantial pathway for energy loss in organic solar cells may be suppressed by engineering hybridization between non-fullerene acceptor triplet excitons and spin-triplet charge transfer excitons.
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| 2. |
- Karki, Akchheta, et al.
(författare)
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Doped semiconducting polymer nanoantennas for tunable organic plasmonics
- 2022
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Ingår i: Communications Materials. - : Springer Nature. - 2662-4443. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical nanoantennas based on organic plasmonics are promising for their higher degree of tunability over metallic nanostructures. Here, nanodisks of polythiophene-based semiconducting polymers provide nanooptical antennas with resonances that are tunable over a 1000 nm wavelength range and can be switched off or on by doping modulation. Optical nanoantennas are often based on plasmonic resonances in metal nanostructures, but their dynamic tunability is limited due to the fixed permittivity of conventional metals. Recently, we introduced PEDOT-based conducting polymers as an alternative materials platform for dynamic plasmonics and metasurfaces. Here, we expand dynamic organic plasmonic systems to a wider class of doped polythiophene-based semiconducting polymers. We present nanodisks of PBTTT semiconducting polymer doped with a dicationic salt, enabling a high doping level of around 0.8 charges per monomer, and demonstrate that they can be used as nanooptical antennas via redox-tunable plasmonic resonances. The resonances arise from the polymer being optically metallic in its doped state and dielectric in its non-conducting undoped state. The plasmonic resonances are controllable over a 1000 nm wavelength range by changing the dimensions of the nanodisks. Furthermore, the optical response of the nanoantennas can be reversibly tuned by modulating the doping level of the polymer. Simulations corroborate the experimental results and reveal the possibility to also modulate the optical nearfield response of the nanoantennas.
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| 3. |
- Karki, Akchheta, et al.
(författare)
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Electrical Tuning of Plasmonic Conducting Polymer Nanoantennas
- 2022
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Ingår i: Advanced Materials. - : Wiley. - 1521-4095 .- 0935-9648. ; 34:13
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructures of conventional metals offer manipulation of light at the nanoscale but are largely limited to static behavior due to fixed material properties. To develop the next frontier of dynamic nano-optics and metasurfaces, this study utilizes the redox-tunable optical properties of conducting polymers, as recently shown to be capable of sustaining plasmons in their most conducting oxidized state. Electrically tunable conducting polymer nano-optical antennas are presented, using nanodisks of poly(3,4-ethylenedioxythiophene:sulfate) (PEDOT:Sulf) as a model system. In addition to repeated on/off switching of the polymeric nanoantennas, the concept enables gradual electrical tuning of the nano-optical response, which was found to be related to the modulation of both density and mobility of the mobile polaronic charge carriers in the polymer. The resonance position of the PEDOT:Sulf nanoantennas can be conveniently controlled by disk size, here reported down to a wavelength of around 1270 nm. The presented concept may be used for electrically tunable metasurfaces, with tunable farfield as well as nearfield. The work thereby opens for applications ranging from tunable flat meta-optics to adaptable smart windows.
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