Direct observation of ultrafast long-range charge separation at polymer:fullerene heterojunctions

Abstract

In polymeric semiconductors, charge carriers are polarons, which means that the excess charge deforms the molecular structure of the polymer chain that hosts it. This effect results in distinctive signatures in the vibrational modes of the polymer. We probe polaron photo- generation dynamics at polymer:fullerene heterojunctions by monitoring its time-resolved resonance-Raman spectrum following ultrafast photoexcitation. We conclude that polarons emerge within 200 fs, which is nearly two orders of magnitude faster than exciton localisation in the neat polymer film. Surprisingly, further vibrational evolution on <50-ps timescales is modest, indicating that the polymer conformation hosting nascent polarons is not signif- icantly different from that in equilibrium. This suggests that charges are free from their mutual Coulomb potential, under which vibrational dynamics would report charge-pair relaxation. Our work addresses current debates on the photocarrier generation mechanism at organic semiconductor heterojunctions, and is, to our knowledge, the first direct probe of molecular conformation dynamics during this fundamentally important process in these materials.

33 pages, please download separately PDF files containing figures (3 figures) and supplementary information

References in corpus (5)

• The Role of Driving Energy and Delocalised States for Charge Separation in Organic Semiconductors
• Exciton Regeneration at Polymeric Semiconductor Heterojunctions
• Highly-Efficient Charge Separation and Polaron Delocalization in Polymer-Fullerene Bulk-Heterojunctions: A Comparative Multi-Frequency EPR & DFT Study
• Noise-induced quantum coherence drives photocarrier generation dynamics at polymeric semiconductor heterojunctions
• Theory of interfacial charge-transfer complex photophysics in $\pi$-conjugated polymer-fullerene blends

Cited by in corpus (12)

• Spatially-resolved Fluorescence-detected Two-dimensional Electronic Spectroscopy Probes Varying Electronic Couplings in Photosynthetic Bacteria
• Do ultrafast exciton-polaron decoherence dynamics govern photocarrier generation efficiencies in polymer solar cells?
• Accessing Excited State Molecular Vibrations by Femtosecond Stimulated Raman Spectroscopy
• Coherent multidimensional spectroscopy in the gas phase
• Non-Markovian quantum-classical ratchet for ultrafast long-range electron-hole separation in condensed phases
• Exciton Dissociation and Charge Separation at Donor-Acceptor Interfaces from Quantum-Classical Dynamics Simulations
• Probing polaron excitation spectra in organic semiconductors by photoinduced-absorption-detected two-dimensional coherent spectroscopy
• Large thermoelectric efficiency of doped polythiophene junction: a density functional study
• An effective Hamiltonian approach for Donor-Bridge-Acceptor electronic transitions: Exploring the role of bath memory
• Exciton dissociation in organic solar cells: An embedded charge transfer state model
• Retrieving genuine nonlinear Raman responses in ultrafast spectroscopy via deep learning
• Evaluation of optical probe signals from nonequilibrium systems