Photon recycling (PR), whereby photons generated by radiative recombination in semiconductors result in the regeneration of electron-hole pairs, plays an important role in the study of optoelectronic semiconductor materials and significantly affects the properties of their applications. In the last decade, PR has been studied and employed in inorganic semiconductor materials and applications. However, PR in low-dielectric-constant exitonic materials, such as organic semiconductors, has not been studied to date. In this work, we investigate the mechanisms of PR in organic semiconductor thin films. We study PR in three different organic semiconducting polymer media (regiorandom poly(3-hexylthiophene-2,5-diyl) (RRa-P3HT), regioregular poly(3-hexylthiophene-2,5-diyl) (RR-P3HT), and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT)) because of their different quantum efficiencies, morphologies and broadband absorptions. In order to study PR, we fabricate different nanostructured surfaces including silver nanoparticle (AgNP) metasurfaces and silver nanograting (AgNG) metasurfaces. In addition, we also use glass, planar Ag and PMMA/Ag surfaces as control groups to analyze the results of PR in the organic thin films compared to the results from nanostructured Ag metasurfaces. Surface-surface photoluminescence (PL) emission spectra (surface excitation and surface emission), edge-edge PL emission spectra (edge excitation and edge emission) and surface-edge PL emission spectra (surface excitation and edge emission) are employed to characterize PR and show strongly red-shifted PL spectra from the sample edge compared to that from the sample surface when PR is strong. Finally, PL lifetime and PL quantum yield results are used to further explain the PR effect in the different organic semiconductor media. This work is expected to lead to greater understanding of the role of PR in affecting the performance of organic thin-film optoelectronic devices.

Photon recycling in organic semiconductor thin films

ACS Spring Meeting 2021

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