Quantitative relationships between film morphology, charge carrier dynamics, and photovoltaic performance in bulk-heterojunction binary vs. ternary acceptor blends
Journal Article
·
· Energy & Environmental Science
- Northwestern Univ., Evanston, IL (United States); Tianjin Univ. (China); OSTI
- Northwestern Univ., Evanston, IL (United States)
- National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
- Northwestern Univ., Evanston, IL (United States); Flexterra Corporation, Skokie, IL (United States)
Addressing pertinent and perplexing questions regarding why nonfullerene acceptors (NFAs) promote higher power conversion efficiencies (PCEs) than traditional fullerenes and how photoactive bulk heterojunction (BHJ) film morphology, charge photogeneration, and recombination dynamics dictate solar cell performance have stimulated many studies of polymer solar cells (PSCs), yet quantitative relationships remain limited. Better understanding in these areas offers the potential to advance materials design and device engineering, afford higher PCEs, and ultimate commercialization. Here we probe quantitative relationships between BHJ film morphology, charge carrier dynamics, and photovoltaic performance in model binary and ternary blend systems having a wide bandgap donor polymer, a fullerene, and a promising NFA. We show that optimal PC71BM incorporation in a PBDB-TF:ITIC-Th binary system matrix retains the original π-face-on orientation, ITIC-Th crystallinity and BHJ film crystallite dimensions, and reduces film upper surface ITIC-Th segregation. Such morphology changes together simultaneously increase hole (μh) and electron (μe) mobilities, facilitate light-activated ITIC-Th to PC71BM domain electron delocalization, reduce free charge carrier (FC) bimolecular recombination (BR) within PBDB-TF:ITIC-Th mixed regions, and increase FC extraction pathways viaPBDB-TF:PC71BM pairs. The interplay of these effects yields significantly enhanced inverted cell short-circuit current density (JSC), fill factor (FF), and PCE. Unexpectedly, we also find that excessive PC71BM in the PBDB-TF:ITIC-Th binary system alters the PBDB-TF orientation to π-edge-on, increases large scale PC71BM-rich aggregations and BHJ upper surface PC71BM composition. Further, these morphology changes increase parasitic decay processes such as intersystem crossing from photoexcited PC71BM, compromising the JSC, FF, and PCE metrics. ITIC-Th X-ray diffraction reveals a unique sidechain-dominated molecular network with previously unknown sidechain-end group stacking, rationalizing the STEM and GIWAXS results, photophysics, and the high μe. DFT computation reveals charge transfer networks within ITIC-Th crystallites, supporting excited-state electron delocalization from ITIC-Th to PC71BM. This structure–property understanding leads to a newly reported NFA blend with PCE near 17%.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS); Brookhaven National Laboratory (BNL), Upton, NY (United States). National Synchrotron Light Source II (NSLS-II); Energy Frontier Research Centers (EFRC) (United States). Center for Light Energy Activated Redox Processes (LEAP); Northwestern Univ., Evanston, IL (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL); Stanford Univ., CA (United States); Univ. of California, Oakland, CA (United States)
- Sponsoring Organization:
- Qatar National Research Foundation; US Department of the Navy, Office of Naval Research (ONR); USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- AC02-05CH11231; AC02-76SF00515; SC0001059; SC0012704
- OSTI ID:
- 2419588
- Alternate ID(s):
- OSTI ID: 1957848
- Journal Information:
- Energy & Environmental Science, Journal Name: Energy & Environmental Science Journal Issue: 3 Vol. 16; ISSN 1754-5692
- Publisher:
- Royal Society of ChemistryCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Similar Records
Enhancing Indacenodithiophene Acceptor Crystallinity via Substituent Manipulation Increases Organic Solar Cell Efficiency
Triptycene as a Supramolecular Additive in PTB7:PCBM Blends and Its Influence on Photovoltaic Properties
Efficient Quaternary Organic Solar Cells with Parallel‐Alloy Morphology
Journal Article
·
Sun Nov 26 19:00:00 EST 2017
· Chemistry of Materials
·
OSTI ID:1470383
Triptycene as a Supramolecular Additive in PTB7:PCBM Blends and Its Influence on Photovoltaic Properties
Journal Article
·
Thu Jun 21 20:00:00 EDT 2018
· ACS Applied Materials and Interfaces
·
OSTI ID:1469621
Efficient Quaternary Organic Solar Cells with Parallel‐Alloy Morphology
Journal Article
·
Mon Jan 07 19:00:00 EST 2019
· Advanced Functional Materials
·
OSTI ID:1490111