Modulating phase segregation during spin-casting of fullerene-based polymer solar-cell thin films upon minor addition of a high-boiling co-solvent

Lu, K.-H.; Wu, W.-R.; Su, C.-J.; Yang, P.-W.; Yamada, N.L.; Zhuo, H.-J.; Chen, S.-A.; Chuang, W.-T.; Lan, Y.-K.; Su, A.-C.; Jeng, U.-S.

doi:10.1107/S1600576724010082

Figure 10
Schematic illustration of the effects of the DIO additive on modulating phase segregation in the PTB7–PC₇₁BM blend during spin-coating from a CB/DIO (97:3 v/v) solution. The high boiling point of DIO accelerates the evaporation of the low-boiling-point CB during the spin-coating process. In the near-surface region (depicted by the graduated blue zone), the rapid evaporation of CB with high flux prevents excessive solute concentration at the surface, thereby inhibiting rapid phase segregation via spinodal decomposition. As CB quickly evaporates, the remaining PC₇₁BM–PTB7 mixture becomes kinetically trapped in the DIO-rich environment, where the slow segregation of PC₇₁BM leads to the formation of small PC₇₁BM aggregates (represented by red spheres) a few nanometres in size. These small aggregates further interconnect into fractal-like clusters within the PTB7/DIO matrix, which consists of both amorphous chains and crystalline regions (depicted as wires and blocks). DIO, accounting for approximately 24% of the film's volume fraction (as estimated from the solution composition after the exhausted evaporation of CB), is represented by the irregular orange patches. In contrast, Fig. 6

illustrates a film from which DIO was removed by vacuum evacuation.

JOURNAL OF
APPLIED
CRYSTALLOGRAPHY

ISSN: 1600-5767

Volume 57| Part 6| December 2024| Pages 1871-1883

https://doi.org/10.1107/S1600576724010082

Open

access

Search IUCr Journals		doi		Advanced search
Author		volume	page