From the beginning of the project, 2 of the 3 work packages (WP) have been fully investigated and addressed.
Year 1 and part of Year 2: the WP1 was fully completed and the milestones and deliverables specified on the project description were addressed completely. The development of the extensive first-principles model of the P3HT:PCBM blend described in the project description took a bit longer than the original time planning due to the high complexity of the model, however, despite this, the delivered investigation and final peer-reviewed publication was successful, and addresses the milestones and goals specified in the WP1 project description. The work related to this WP includes the initial production of source-codes, data manipulation and analysis and results production. All these self-written codes and scripts were used to elaborate the first-principles model using quantum (TDDFT calculations) and classical (Molecular Dynamics) simulations. The intensive model introduces a complete first-principles description of a prototypical realistic P3HT:PCBM photovoltaic blend (1480 PCBM molecules, 845 P3HT molecules) which includes a quantum mechanical description of the photoinduced exciton delocalisation in the electron donor system (P3HT) in the time-dependent (picoseconds timescale) fluctuating environment determined by the P3HT-PCBM blend. This novel model reveals the origin of the homogeneous and inhomogeneous broadening in the simulated linear and two-dimensional spectra of the P3HT:PCBM blend, identifying the role of the environment on the exciton delocalisation after photexcitation, that controls the extent of the charge-transfer process. An extensive configurational analysis of the torsional flexibility along the P3HT chains in the presence of the fluctuating environment and its effect on the exciton delocalisation is performed. The insights from WP1 have been disseminated in 4 international conferences (3 talks and 1 poster) and published in one peer-reviewed publication with open-access (JPCC). Besides, this work was selected to be published as part of The Journal of Physical Chemistry virtual special issue “Early-Career and Emerging Researchers in Physical Chemistry Volume 2”. These developments introduce a quantum-classical description of the exciton delocalisation in a prototypical OPV material (P3HT:PCBM blend) including a extensive description of the role of the environment on the simulated spectra, directly comparable to available experiments.
Year 2: WP2 and part of WP3 were performed. A low-dimensional nonadiabatic model was developed and the explicit effect of the light-driven quantum dynamics for different pulse excitation conditions was investigated. First, a single-pulse dynamics was investigated. An extensive analysis was done of the effect of chirped pulse excitations on the photoinduced electronic wavepacket. The analysis reveals that chirped pulses can be used to manipulated the extent of the charge-transfer in the electron donor-acceptor model, for long times after dissipation (bath/blend). Last, 2-pulse fluorescence time-resolved spectra were simulated and introduced, demonstrating that chirped pulses can be used to enhanced the system dynamical information. This work is presented in a manuscript ready for submission and these insights have been disseminated in 2 talks at international conferences.
