Unipolar Injection and Bipolar Transport in Electroluminescent Ru-Centered Molecular Electronic Junctions
Bibliographic record
Abstract
Bias-induced light emission and light-induced photocurrents were used as independent probes of charge transport in carbon-based molecular junctions containing Ru(bpy)3. The thickness, bias, and temperature dependence of both the total device current and photoemission were compared, as well as their response to bias pulses lasting from a few milliseconds to several seconds. The device current was exponentially dependent on the square root of the applied electric field, with weak dependence on thickness when compared at a constant field. In contrast, light emission was strongly dependent on thickness at a given electric field, with a thickness-independent onset for light emission and a large intensity increase when the bias exceeded the 2.7 V HOMO–LUMO gap of Ru(bpy)3. The apparent activation energies for light emission and current were similar but much smaller than those expected for thermionic emission or redox exchange. Light emission lagged current by several milliseconds but reached maximum emission in 5–10 ms and then decreased slowly for 1 s, in contrast to previously reported solid-state Ru(bpy)3 light-emitting devices that relied on electrochemical charge injection. We conclude that at least two transport mechanisms are present, that is, “unipolar injection” initiated by electron transfer from a Ru(bpy)3 HOMO to the positive electrode and “bipolar injection” involving hole and electron injection followed by migration, recombination, and light emission. The unipolar mechanism is field-driven and the majority of the device is current, while the bipolar mechanism is bias-driven and involves electrode screening by PF6 ions or mobile charges. In addition, significant changes in thickness and temperature dependence for thicknesses exceeding 15 nm imply a change from injection-limited transport to bulk-limited transport. The current results establish unequivocally that electrons and holes reside in the molecular layer during transport once the transport distance exceeds the ∼5 nm limit for coherent tunneling and that redox events involving nuclear reorganization accompany transport. In addition, they demonstrate luminescence in a single organometallic layer without hole or electron transport layers, thicknesses below 30 nm, and symmetric electrodes with similar work functions.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".