The efficiency of organic solar cell is closely dependent on the morphology or spatial organization of electron donor and acceptor materials within the active layer. Understanding the morphology of this active layer would be inevitably helpful for power conversion efficiency improvement of organic solar cells. Here, we employed molecular dynamics (MD) simulations with coarse-grained (CG) model that featured the large-scale morphology organization of donor (poly(3-hexyl-thiophene) (P3HT)) and acceptor (phenyl-C61-butyric acid methyl ester (PCBM)) using solvent evaporation and thermal annealing methods. We were able to generate two different types of configurations that were commonly reported by experiment: bulk PCBM (fullerene-rich region), and P3HT:PCBM bilayer (interface). We then back mapped the CG morphology to atomistic detail for recovering the structural specificity. With the application of mixed quantum/classical approach, we computed the ester carbonyl stretch vibrational spectra of PCBM and they are in good agreement with experiment. Due to the high sensitivity of ester carbonyl stretch from PCBM, we observed spectra blue shifted 3 cm<sup>-1</sup> when PCBM interfaced with P3HT comparing to bulk. With further explorations from MD, we found hydrogen atoms from PCBM dominantly influenced local electric field environment around carbonyl group from PCBM and further resulted in the observed spectral shift. Moreover, the side chain of PCBM was also found to exhibit different distributions with PCBMs in bulk compared to interface.

Unveiling (the molecular/microscopic structure of) the P3HT/PCBM interface by infrared spectroscopy of ester carbonyl stretch

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.