Structural study of dissymmetric systems of the thymenopyrazine-based structure D-pi-A for bulk heterojunction (BHJ) organic solar cells

摘要

Eleven new organic molecules of donor-spacer-acceptor (D-pi-A) structure used for organic solar cells (OSCs) based on thiopyrazine and thiophen were studied by means of functional density theory (DFT) and time dependent functional density theory (TD-DFT), to explain how the order of conjugation affects the performance of solar cells. The electron acceptor (anchor) group was composed of 2-cyanoacrylic for all compounds, while the electron donor unit varied and its influence was studied. Theoretical results showed that the TD-DFT calculations, with a hybrid exchange function - correlation using the Coulomb attenuation method (CAM-B3LYP) together with a polarizable continuous cycle (polarizable continuum model, PCM) solvation model combined with the 6-31G(d,p) base, proved capable of predicting the excitation energies and absorption and emission spectra of the molecules considered reasonably well. The energy levels of the frontier molecular orbitals (HOMO and LUMO) of these compounds can have a positive impact on the electron injection and regeneration process. The trend of calculated HOMO-LUMO gaps compares well with spectral data. In addition, the estimated open circuit photovoltage (V-oc)-values for these compounds were presented. The study of the structural, electronic, and optical properties of these compounds could help in the design of more efficient functional photovoltaic organic materials.