Thin-film conjugated polymer materials are emerging as versatile alternatives to inorganic semiconductors for photovoltaic, display and solid-state lighting applications. Additionally, polymer-based optoelectronic devices can exhibit small device embodied energies (due to comparatively low temperature and low energy-use fabrication processes) which is of interest for reducing the overall optoelectronic device cost and life-cycle energy consumption. However, further improvements in the energy conversion efficiency in thin-film conjugated polymer-based optoelectronics are necessary and require effective nanophotonic light management such as nanoscale light trapping and light extraction.<br/>Here we show that the morphology of conjugated polymer and conjugated polymer:fullerene thin films on nanostructured metal electrodes strongly influences whether nanophotonic and plasmonic electromagnetic modes are absorbed or out-coupled (leaked) from the polymer-based thin films. Using optical dark-field scattering, full-field electromagnetic modelling and grazing-incidence, wide-angle X-ray scattering, we find that more crystalline polymer-based active layers, such as P3HT and P3HT:PCBM, trap surface plasmons, while more amorphous thin films, such as PCDTBT and PTB7:PC<sub>70</sub>BM, facilitate leakage of surface plasmon polaritons. This is an important finding because it indicates that light trapping is improved using crystalline polymer thin-films; while more efficient light extraction is possible using amorphous polymer films.<br/>Furthermore, our recent work on improving light-emission from conjugated polymer thin films on nanostructured metal electrodes by controlling polymer morphology will be presented. Numerous optical phenomena, such as absorption-induced scattering, out-of-plane waveguiding and morphology-dependent surface plasmon outcoupling, are identified due to exciton-plasmon coupling between the conjugated polymer excitons and the nanostructured metal electrode surface. Interactions between localized and propagating surface plasmons and the excitonic transitions of conjugated polymer materials with a range of bandgaps and photoluminescence quantum efficiencies will be discussed, and ways in which these interactions may be optimized for particular optoelectronic applications will be presented.

Influence of conjugated polymer thin-film morphology and exciton-plasmon coupling on nanophotonic light trapping and light extraction

253rd National Meeting (2017)

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