Open AccessSinglet Exciton Fraction in Electroluminescence from Conjugated Polymer
Author(s) -
TzuHao Jen,
ShowAn Chen
Publication year - 2017
Publication title -
scientific reports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.24
H-Index - 213
ISSN - 2045-2322
DOI - 10.1038/s41598-017-02115-2
Subject(s) - electroluminescence , conjugated system , exciton , singlet state , fraction (chemistry) , polymer , materials science , optoelectronics , photochemistry , chemistry , physics , condensed matter physics , atomic physics , nanotechnology , organic chemistry , composite material , excited state , layer (electronics)
The efficiency of electrofluorescent polymer light-emitting diodes is determined by singlet exciton fraction (χ S ) formation and its value still remains controversial. In this work, χ S in spiropolyfluorene (SPF) is determined by analyzing transient emission of phosphor-dopant probe. The χ S is found to range from 50% to 76%, depending on applied voltage. Higher applied voltage gives larger χ S . Besides, more rapid increment in χ S with applied voltage is observed in the higher-molecular-weight polymer. The voltage or molecular weight dependence of χ S suggests the probability of singlet exciton (SE) generation through triplet-triplet annihilation (TTA) is enhanced due to higher triplet exciton (TE) concentration at higher applied voltage or accommodation of more TEs in a polymer chain with high molecular weight, thereby increasing probability of TTA. At lower applied voltage, χ S is contributed by charge recombination. Its value (χ S ~50%) higher than the statistical limit 25% is in agreement with efficient interconversion between triplet and singlet polaron pairs (PP) and with larger formation rate of SE relative to that of TE.