Polymer light-emitting electrochemical cells : frozen-junction operation of an “ionic liquid” device

• We report frozen-junction operation of a polymer light-emitting electrochemical cell containing a mixture of poly[2-methoxy-5-(2(')-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and the ionic liquid tetra-n-butylammonium trifluoromethanesulfonate (TBA-TF) as the active material. We find fast turn-on time, unipolar light emission, and significant operational lifetime up to T=200 K for planar Au/(TBA-TF+MEH-PPV)/Au surface cells, which had been charged (i.e., electrochemically p- and n-type doped in situ) at T=393 K and V=4 V and then cooled to 80 K at V=4 V. We employed differential scanning calorimetry to demonstrate that (TBA-TF+MEH-PPV) exhibits two melting transitions of TBA-TF crystalline phases located at T(m,1)approximate to 280 K and T(m,2)approximate to 380 K, respectively. The lower T-m,T-1 sets the upper limit for frozen-junction operation (with zero-ionic conductivity), while the larger T-m,T-2 correlates to the lower limit for the charging regime (with high ionic conductivity).

Ämnesord

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Nyckelord

I-N junction

morphology

stability

efficient

kinetics

salt

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