Distribution of space charges in luminescent conjugated polymers

Abstract

We present investigations of the distribution of space charges in thin films of conjugated polymers. A thermal wave method (LIMM) has been used to resolve the depth profile of space charges and the distribution of the internal electric field in 3–4 µm films of poly(2,5‐pyridinediyl), the poly(p‐phenylenvinylene) derivative poly[2‐methoxy,5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylenvinylene] (MEH‐PPV) and polyfluorine (PFO). The results demonstrate that in conjugated polymers, space charges cannot only be created but can also be stored permanently. The electric field in the bulk of the film is significantly reduced because of the existence of two space charge layers: a narrow, positively charged layer at the front electrode, and a broader, negatively charged layer at about 500 nm. We assign the positive layer to the injection of positive charge carriers from the anode into near surface traps, and the second hetero‐charge layer to bulk charges that have been separated within the external electric field and accumulated in the trapping zone. The dynamics of the accumulation and poling of the space charge layers has been investigated by means of measurements of the temporal evolution and temperature dependence of the pyroelectric response. © 2002 Society of Chemical Industry

Asymmetric polarization and hysteresis behaviour in ferroelectric P(VDF–TrFE) (76 : 24) copolymer thin films spatially resolved via LIMM

“…LIMM is a particularly useful method for the investigation of spatially resolved polarization and charge distributions in ferroelectric materials. 27,28 The technique probes a sample using thermal waves of different frequencies. The resulting pyroelectric current spectrum can be deconvoluted or transformed to a polarization depth profile.…”

Delayed recombination of detrapped space-charge carriers in poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene]-based light-emitting diode

“…3, the DEF is found to be increasingly quenched as the bias offset is changed from forward to reverse polarity. [28][29][30][31] Such traps are chemical defects of the polymer chain or can be introduced during the synthesis or during the device preparation. These findings suggest that recombination of detrapped space-charge carriers should be responsible for the observed DEF.…”