Time-resolved imaging of carrier transport in halide perovskite thin films and evidence for nondiffusive transport
Bibliographic record
Abstract
Owing to their exceptional semiconducting properties, hybrid inorganic-organic perovskites show great promise as photovoltaic absorbers. In these materials, long-range diffusion of charge carriers allows for most of the photogenerated carriers to contribute to the photovoltaic efficiency. Here, time-resolved photoluminescence (PL) microscopy is used to directly probe ambipolar carrier diffusion and recombination kinetics in hybrid perovskites. This technique is applied to thin films of methylammonium lead tri-iodide $(\mathrm{MAPb}{\mathrm{I}}_{3})$ obtained with two different fabrication routes, methylammonium lead tribromide $(\mathrm{MAPbB}{\mathrm{r}}_{3})$, and an alloy of formamidinium lead tri-iodide and methylammonium lead bromide $\mathrm{F}{\mathrm{A}}_{0.85}\mathrm{M}{\mathrm{A}}_{0.15}\mathrm{Pb}{({\mathrm{I}}_{0.85}\mathrm{B}{\mathrm{r}}_{0.15})}_{3}$. Average diffusion coefficients in the films leading to the highest device efficiencies and longest lifetimes, i.e., in $\mathrm{F}{\mathrm{A}}_{0.85}\mathrm{M}{\mathrm{A}}_{0.15}\mathrm{Pb}{({\mathrm{I}}_{0.85}\mathrm{B}{\mathrm{r}}_{0.15})}_{3}$ and acetonitrile-processed $\mathrm{MAPb}{\mathrm{I}}_{3}$, are found to be several orders of magnitude lower than in the other films. Further examination of the time dependence shows strong evidence for nondiffusive transport. In particular, acetonitrile-processed $\mathrm{MAPb}{\mathrm{I}}_{3}$ shows distinct diffusion regimes on short and long timescales with an effective diffusion constant varying over 2 orders of magnitude. Our results also highlight the fact that increases in carrier lifetime in this class of materials are not necessarily concomitant with increased diffusion lengths and that the PL quantum efficiency under solar cell operating conditions is a greater indication of material, and ultimately device, quality.
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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 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".