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Real-Time Probing of Morphological Evolution and Recrystallization During Solvent Annealing in Blade-Coated
Jialiang Hao1,2, Yang Feng1,3, Qianyi Ma1,4
1Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai, 201204, China.
Optimizing all-polymer solar cells (APSCs) requires controlling active layer morphology. This study uses in situ techniques to reveal morphological evolution during solvent vapor annealing (SVA), boosting power conversion efficiency (PCE) by 15.1%.
Area of Science:
- Materials Science
- Photovoltaics
- Polymer Chemistry
Background:
- Optimizing active layer morphology is critical for high photovoltaic conversion efficiency in all-polymer solar cells (APSCs).
- Solvent vapor annealing (SVA) is a key post-treatment for morphology control, but ex situ methods limit understanding of in-situ evolution.
- Real-time monitoring is needed to accurately reveal morphological changes during APSC active layer formation.
Purpose of the Study:
- To investigate the real-time morphological evolution of PM6/PY-IT blends during solvent vapor annealing (SVA).
- To understand the impact of different solvent polarities on blend morphology and device performance.
- To elucidate the stages of SVA and the role of pre-annealing in optimizing APSC morphology and efficiency.
Main Methods:
- In situ synchrotron radiation grazing incidence wide-angle X-ray scattering (GIWAXS) and grazing incidence small-angle X-ray scattering (GISAXS).
- In situ UV-vis spectroscopy to monitor changes in polymer blend absorption.
- Controlled solvent vapor annealing (SVA) with nonpolar (carbon disulfide) and polar (chloroform) solvents.
Main Results:
- PY-IT absorption showed a red shift with carbon disulfide and a blue shift with chloroform during SVA.
- The SVA process was characterized by three distinct stages: solvent swelling, recrystallization, and molecular rearrangement.
- Thermally pre-annealed samples treated with chloroform SVA achieved a 15.1% increase in power conversion efficiency (PCE).
- Improved PCE correlated with reduced crystal plane spacing, enhanced crystal coherence length, and optimized phase separation.
Conclusions:
- In situ monitoring provides crucial insights into the dynamic morphological evolution during SVA of APSCs.
- Balancing SVA conditions, including solvent choice and pre-annealing, is essential for maximizing APSC performance.
- Pre-annealing plays a significant role in suppressing excessive swelling and promoting molecular rearrangement for optimal morphology.
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