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Title: Charge separation dynamics at bulk heterojunctions between poly(3-hexylthiophene) and PbS quantum dots

Photo-induced electron transfer between poly-(3-hexylthiophene) (P3HT) and small (2.4 nm) PbS quantum dots (QDs), capped by different ligands, was studied by picosecond and femtosecond time-resolved fluorescence and by photo-induced absorption (PIA) measurements. In line with previous experiments, we observed that the efficiency of the quenching of P3HT by PbS QDs increased upon decreasing the average thickness of the ligand shell. This trend was also observed in the PIA spectra and in prior work on the performance of photovoltaic devices where the active layer was a blend of P3HT with PbS QDs capped by different ligands. Combining the pico- and femtosecond fluorescence decays showed that the quenching in blend films of P3HT and PbS QDs treated with 1,4-benzenedithiol occurred over a broad time scale ranging from tens of femtoseconds to hundreds of picoseconds. This complex kinetics was attributed to exciton hopping followed by electron transfer to the conduction band of the QDs. We also compared the wavelength dependence of the internal quantum efficiency (IQE) in the hybrid photovoltaic devices to those devices where the photoactive layer consists of PbS QDs only. Although excitation in the first excitonic transition of the PbS QDs yielded a similar IQE in both devices, the IQE ofmore » the hybrid devices tripled at wavelengths where also P3HT started to absorb. This suggests that upon excitation of P3HT in the latter devices, charge generation occurs by photo-induced electron transfer from P3HT to the QDs rather than by energy transfer to the QDs followed by exciton dissociation in the QDs.« less
Authors:
; ; ;  [1] ; ; ;  [2] ; ;  [3]
  1. Laboratory of Photochemistry and Spectroscopy, Division of Molecular Imaging and Photonics, Chemistry Department, KULeuven, Celestijnenlaan 200F, B2404, 3001 Leuven (Belgium)
  2. Department of Physics, Energy and Semiconductor Research Laboratory, University of Oldenburg, Carl-von-Ossietzky-Str. 9-11, 26129 Oldenburg (Germany)
  3. Imec vzw, Kapeldreef 75, 3001 Leuven (Belgium)
Publication Date:
OSTI Identifier:
22494711
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 5; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ABSORPTION; DISSOCIATION; ELECTRON TRANSFER; ENERGY TRANSFER; EXCITATION; FLUORESCENCE; FREQUENCY DEPENDENCE; HETEROJUNCTIONS; LEAD SULFIDES; PHOTOVOLTAIC EFFECT; QUANTUM DOTS; QUANTUM EFFICIENCY; QUENCHING; THIN FILMS; THIOPHENE; TIME RESOLUTION; WAVELENGTHS