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(a) Depiction of the main device architecture consisting of Al on a PbS nanocrystal (NC) film. The inset shows a SEM of the nanocrystal film (scale bar is ). (b) The energy band model, illustrating the presence of bending in the conduction band , valence band , and vacuum energy near the Al/nanocrystal interface. Photogenerated electron and hole transport is governed by the presence of a built-in electric field within the depletion layer (of width ) of the nanocrystal layer (of thickness ). The Fermi level is drawn to show the -type conduction characteristics. The bandgap of these nanocrystals is , defined by the first maximum in the absorption spectrum.
The current-voltage curve and photovoltaic performance (under , illumination) for a device processed using the optimized passivation (dashed black, curve 2) procedure compared to the baseline (solid black, curve 1), showing an increase in . Nanocrystals having undergone both the optimized passivation and ligand exchange procedures (bold blue, curve 3) yielded devices with enhanced and EQE compared to the baseline; this is emphasized by the enclosure that represents the maximum power load conditions. FF: fill factor and PCE: power conversion efficiency.
(a) Comparison of the current-voltage characteristics for design A in the dark and under illumination from variations of the simulated solar illumination source. (b) Current-voltage curves for design A (under illumination) and design B (under illumination). (c) EQE spectra for designs A and B. The inset shows the absorption spectra of the ligand-exchanged nanocrystals in solution; excitonic peaks were also visible in the film absorption spectra. au: arbitrary units.
Device performance parameters; all data were obtained using design A, except under illumination, where design B was used. , intensity, , short-circuit current density; PCE, power conversion efficiency.
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