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Updated: Dec 10, 2025
Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization
Published on: January 29, 2017
Morphology Changes Upon Scaling a High-Efficiency, Solution-Processed Solar Cell From Spin-Coating to Roll-to-Roll
Hyun Wook Ro1, Jonathan M Downing1, Sebastian Engmann1
1Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
Roll-to-roll coating enables low-cost solar cell production. Scalable blade-coating techniques yield high-efficiency PffBT4T-2OD solar cells with diverse morphologies, challenging previous assumptions about optimal bulk heterojunction structures.
Area of Science:
- Materials Science
- Renewable Energy
- Polymer Science
Background:
- Roll-to-roll (R2R) coating offers a sustainable, low-cost method for solar cell manufacturing.
- High power conversion efficiency (PCE) in polymer solar cells often relies on specific film morphologies achieved through spin-coating.
- Poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)-2,2';5',2″;5″,2‴-quaterthiophen-5,5-diyl)] (PffBT4T-2OD) has shown promise for high-efficiency solar cells.
Purpose of the Study:
- To investigate the morphology of PffBT4T-2OD based bulk heterojunction (BHJ) films produced by scalable R2R compatible techniques (blade-coating and slot-die coating).
- To compare the morphology and device performance of R2R coated films with those produced by spin-coating.
- To challenge existing notions of optimal BHJ morphology for high-performance solar cells.
Main Methods:
- Deposition of PffBT4T-2OD BHJ films using blade-coating and slot-die coating techniques.
- Detailed morphology studies, including crystal domain orientation and phase separation length scales.
- In situ measurements to understand film solidification processes during coating.
- Fabrication and characterization of optimized blade-coated solar cell devices.
Main Results:
- Significant differences in film morphology (crystal orientation, phase separation) were observed between scalable coating techniques and spin-coating.
- Optimized blade-coated devices achieved a PCE greater than 9.5%, comparable to spin-coated devices.
- In situ measurements revealed distinct solidification routes for spin- and blade-coating, leading to different film structures.
Conclusions:
- High PCE can be achieved with BHJ morphologies distinct from those typically obtained via spin-coating.
- Morphological diversity supporting high performance may be a characteristic of manufacturable solar cell systems.
- Scalable R2R techniques like blade-coating are viable for producing high-efficiency polymer solar cells with thicknesses exceeding 200 nm.
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