How the Size and Density of Charge-Transfer Excitons Depend on Heterojunction’s Architecture

We have characterized the size, intensity, density, and distribution of charge-transfer (CT) excitons as a function acceptor–donor architecture prototypical organic interfaces. This characterization was done by computational analysis 17 models varying numbers, positions, orientations donor acceptor molecules. The models’ building blocks were phenyl-C61-butyric acid methyl ester (PCBM) fullerene acceptors dual-band polymers composed thiophene, benzothiadiazole, benzotriazole subunits. electronic structure donor–acceptor complexes computed with time-dependent long-range-corrected density-functional tight-binding method analyzed fragment-based one-electron transition density matrix. In all models, edge-on orientation denser spectra low-energy CT states lying below absorption bands compared to face-on orientation. CT-state in provides gate efficiently populate cold excitons. Moreover, higher degree charge separation than complexes. amount exciton size generally increase energy states, although electron remains localized on single molecule states. Delocalization over two PCBM molecules observed for high-energy also depends Larger are produced delocalization electrons perpendicularly interface. When is parallel, smaller electron–hole distances yield moderately sized