Irreversible primary processes in ITO/TPD/Alq3/Al OLEDs at low bias voltage: on the electrical fatigue of OLEDs
Bibliographic record
Abstract
OLEDs based on ITO as anode, TPD/Alq3 as organic PN junction, and Al as cathode, represent an important standard model. Since TPD and Alq3 are thin layers (< 100 nm), even at low bias voltage, V (~1 V), the electric field is relatively high (~108 V/m). During the very first bias voltage application to ITO/TPD/Alq3/Al OLEDs, some unexpected currents add to the injection of electrons and holes. These “primary processes” induce irreversible structural alterations in OLEDs. This conclusion is based on the fact that the forward bias current-voltage characteristic curves, I-V, systematically show a first scan that is very different from all subsequent ones. Below 4 V, the first scan shows two current “bumps” (near 1 V and 2.5 V). The current density is ~1 mA/cm2. For all subsequent scans, the bumps disappear, and the current density decreases to ~10 μA/cm2. Above 3 V, the I-V curves show current “spikes”, up to ~100 μA/cm2. Since no light is emitted when the bumps and spikes occur, these current surges are not due to electron-hole recombination. We suggest that four processes occur nearly simultaneously: (1) ionic transport due to ions uniformly distributed inside the organic layers, (2) ionic transport similar to the propagation of a Haynes-Shockley current pulse, (3) electrochemical cathode oxidation via the Cabrera-Mott mechanism, (4) sporadic rotations of organic molecules, similarly to liquid crystals and responsible for current spikes. Processes (1) and (2) are both responsible for the first bump, while (3) and (4) are both linked to the second bump. The theoretical model developed for the I-V characteristic curves agrees well with measurements. These irreversible primary processes could be partly responsible for OLEDs aging.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".