Coherent Charge Transfer Exciton Formation in Regioregular P3HT: A Quantum Dynamical Study

Area of Science:

• Organic Electronics
• Photophysics
• Quantum Dynamics

Background:

• Regioregular poly(3-hexyl thiophene) (rrP3HT) is a key material in organic electronics.
• Understanding exciton formation and dynamics is crucial for device efficiency.
• Charge transfer excitons (CTXs) play a significant role in charge separation.

Purpose of the Study:

• To elucidate the ultrafast formation of CTXs in rrP3HT.
• To investigate the role of vibronic coupling in CTX dynamics.
• To explain the origin of coherent oscillations observed in time-resolved spectroscopy.

Main Methods:

• Electronic structure calculations using Time-Dependent Density Functional Theory (TDDFT).
• Development of a multistate vibronic coupling Hamiltonian.
• Quantum dynamical simulations using the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method.

Main Results:

• CTX formation occurs immediately upon photoexcitation in the model system.
• Sustained coherent oscillations with a ~22 fs periodicity are observed.
• High-frequency CC stretch vibrational modes are identified as the source of these coherent features.

Conclusions:

• The study reveals the ultrafast nature of CTX formation in rrP3HT.
• Collective vibronic response, driven by CC stretch modes, enhances vibrational signatures.
• This provides a microscopic explanation for observed coherent phenomena in organic semiconductor films.