Quantitative Characterization and Mechanism of Formation of Multilength-scale Bulk Heterojunction Structures in Highly Efficient Solution-Processed Small-Molecule Organic Solar Cells

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• 作者：Yu-Ching Huang ; Cheng-Si Tsao ; Tzu-Yen Huang ; Hou-Chin Cha ; Dhananjaya Patra ; Chun-Jen Su ; U-Ser Jeng ; Kuo-Chuan Ho ; Kung-Hwa Wei ; Chih-Wei Chu
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：July 23, 2015
• 年：2015
• 卷：119
• 期：29
• 页码：16507-16517
• 全文大小：580K
• ISSN：1932-7455

文摘

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鈥揇鈥揂-type 蟺-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.