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Published on: January 10, 2017
Stable Postfullerene Solar Cells via Direct C-H Arylation Polymerization. Morphology-Performance Relationships
Thomas J Aldrich1, Weigang Zhu1, Subhrangsu Mukherjee2
1Department of Chemistry, the Center for Light Energy Activated Redox Processes (LEAP), and the Materials Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
Environmentally friendly direct C-H arylation polymerization (DARP) creates novel benzodithiophene copolymers for polymer solar cells (PSCs). These DARP-derived PSCs achieve high power conversion efficiencies (PCEs) and demonstrate promising stability.
Area of Science:
- Materials Science
- Polymer Chemistry
- Renewable Energy
Background:
- Direct C-H arylation polymerization (DARP) offers an environmentally benign route for synthesizing advanced polymer materials.
- Benzodithiophene-based copolymers are crucial for high-performance polymer solar cells (PSCs).
- Nonfullerene acceptors (NFAs) are increasingly important for efficient PSCs.
Purpose of the Study:
- To extend the scope of the DARP process for synthesizing a series of benzodithiophene-based copolymers (PBDT(Ar)-FTTE) with varied heteroaryl substituents.
- To fabricate and evaluate bulk-heterojunction (BHJ) PSCs using these DARP-derived donors and the NFA ITIC-Th.
- To elucidate structure-property relationships influencing PSC performance and stability.
Main Methods:
- Synthesis of PBDT(Ar)-FTTE copolymers via DARP.
- Fabrication of PSCs with PBDT(Ar)-FTTE donors and ITIC-Th acceptor.
- Characterization using SCLC, AFM, GIWAXS, R-SoXS, and NEXAFS to analyze structural order, BHJ morphology, and charge transport.
- Performance evaluation including power conversion efficiency (PCE), fill factor (FF), and short-circuit current (JSC).
- Stability testing under ambient conditions and simulated solar illumination.
Main Results:
- DARP successfully synthesized a series of PBDT(Ar)-FTTE copolymers with tunable heteroaryl substituents.
- PSCs fabricated with these donors and ITIC-Th achieved PCEs up to 8%.
- Smaller, well-blended BHJ copolymer domains correlated with enhanced JSC, FF, and PCE.
- One specific copolymer, PBDTTF-FTTE, demonstrated optimal initial photovoltaic metrics and stability, retaining ~90% PCE after 51 days.
- PSC stability correlated with large pure BHJ domains and rivaled fullerene-based PSCs.
Conclusions:
- The DARP process is a viable and versatile method for creating high-performance benzodithiophene-based copolymers for PSCs.
- Tuning heteroaryl substituents and controlling BHJ morphology are critical for optimizing PSC performance and stability.
- DARP-processed solar cells utilizing NFAs show potential for greener and more stable solar energy generation.
