Quantitative Characterization and Mechanism of Formation of Multilength-scale Bulk Heterojunction Structures in Highly Efficient Solution-Processed Small-Molecule Organic Solar Cells
Journal
Journal of Physical Chemistry C
Journal Volume
119
Journal Issue
29
Pages
16507-16517
Date Issued
2015
Author(s)
Huang, Y.-C.
Tsao, C.-S.
Huang, T.-Y.
Cha, H.-C.
Patra, D.
Su, C.-J.
Jeng, U.-S.
Ho, K.-C.
Wei, K.-H.
Chu, C.-W.
Abstract
In this study we used simultaneous grazing-incidence small- and wide-angle X-ray scattering (GISAXS and GIWAXS, respectively) to probe the multilength-scale structures of thin active layers comprising the linear A-D-A-type π-conjugated donor molecule TBDTCNR and the fullerene acceptor molecule PC61BM for use in solution-processed small-molecule-based organic solar cells (SMOSCs). We found that the pseudo-two-dimensional fractal-like networks in the bulk heterojunction (BHJ) structure were determined by mutual interactions between the small-molecule (SM) crystallites and the nanoscale PC61BM clusters during their formation and phase separation, and deduced quantitatively, at multiple length scales, the BHJ structures comprising these SM crystallites and PC61BM clusters. We also conducted in situ GIWAXS measurements to study the temporal behavior and kinetics of SM crystallization from solution to the solid film state. Our GISAXS/GIWAXS study revealed that the multilength-scale BHJ structures in the thin films could be tuned effectively by varying the amount of incorporated PC61BM and the annealing temperature. This study provides fundamental information relating to the mechanism of formation of hierarchical BHJ structures through relatively rapid crystallization of a highly crystalline SM, as well as the relationships among the hierarchical structure, the photovoltaic performance, and the mechanism of formation, thereby allowing greater control over BHJ structures in SMOSCs with optimized fabrication and performance. © 2015 American Chemical Society.
SDGs
Other Subjects
Crystallites; Heterojunctions; Molecules; Organic polymers; Phase separation; X ray scattering; Annealing temperatures; Bulk heterojunction (BHJ); Bulk-heterojunction structure; Hierarchical structures; Photovoltaic performance; Quantitative characterization; Small and wide angle x ray scatterings; Small-molecule organic solar cells; Solar cells
Type
journal article