RESUMO
Coarse grained molecular dynamics simulations are performed for a mixture of poly(3-hexylthiophene) (P3HT) and diperylene bisimide (DiPBI). The effect of different annealing and cooling protocols on the morphology is investigated and the resulting domain structures are analyzed. In particular, π-stacked clusters of DiPBI molecules are observed whose size decreases with increasing temperature. Domain structure and diffusivity data suggest that the DiPBI subsystem undergoes an order â disorder phase transition between 700 and 900 K. Electronic structure calculations based on density functional theory are carried out after backmapping the coarse grained model onto an atomistic force field representation built upon first principles. UV/vis absorption spectra of the P3HT:DiPBI mixture are computed using time-dependent density functional linear response theory and recorded experimentally for a spin-coated thin film. It is demonstrated that the absorption spectrum depends sensitively on the details of the amorphous structure, thus providing valuable insight into the morphology. In particular, the results show that the tempering procedure has a significant influence on the material's electronic properties. This knowledge may help to develop effective processing routines to enhance the performance of bulk heterojunction solar cells.
RESUMO
Optical absorption spectra of poly(3-hexylthiophene) (P3HT) are calculated in solution, spin-coated thin films, and the bulk crystal using a multiscale simulation approach. The structure of the amorphous thin film is obtained from coarse grained molecular dynamics (MD) simulations and subsequent back-mapping onto an atomistic force field representation. The absorption spectra are computed using TDDFT by statistically averaging over an ensemble of molecules taken from the MD simulations. Experimental UV/Vis spectra of spin-coated thin films and solutions are recorded with varying ratios of 'good' versus 'poor' solvent. The theoretical approach is able to faithfully predict the spectral position in the various phases and offers fundamental insight into the cause of any spectral shifts. The position of the main absorption peak is found to be chiefly determined by the level of torsion between the thiophene rings inside each molecule, while intermolecular effects are less important. Hence, optical absorption spectra hold valuable clues about the microscopic structure of disordered P3HT phases.
RESUMO
A new photorefractive (PR) material sensitized with a novel functional unit DiPBI is prepared based on the guest/host approach. This unique mixture exhibits strong absorption in the whole range of visible light. Moreover, the photorefractive performance as well as PR speed is improved by far compared to the widely used sensitizer PCBM.
