Journal
NANO LETTERS
Volume 11, Issue 9, Pages 3707-3713Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nl201715q
Keywords
Organic photovoltaics; bulk heterojunction; hierarchical nanomorphology; charge photogeneration; X-ray scattering; device performance
Categories
Funding
- Argonne Director's Postdoctoral Fellowship
- NSF
- NSF-MRSEC
- AFOSR
- DOE
- University of Chicago-Argonne Strategic Collaborative Initiative
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
- Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U.S. Department of Energy
- U.S. Department of Energy Office of Science laboratory [DE-AC02-06CH11357]
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [1004195] Funding Source: National Science Foundation
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PTB7 semiconducting copolymer comprising thieno[3,4-b]thiophene and benzodithiophene alternating repeat units set a historic record of solar energy conversion efficiency (7.4%) in polymer/fullerene bulk heterojunction solar cells. To further improve solar cell performance, a thorough understanding of structure-property relationships associated with PTB7/fullerene and related organic photovoltaic (OPV) devices is crucial. Traditionally, OPV active layers are viewed as an interpenetrating network of pure polymers and fullerenes with discrete interfaces. Here we show that the active layer of PTB7/fullerene OPV devices in fact involves hierarchical nanomorphologies ranging from several nanometers of crystallites to tens of nanometers of nanocrystallite aggregates in PTB7-rich and fullerene-rich domains, themselves hundreds of nanometers in size. These hierarchical nanomorphologies are coupled to significantly enhanced exciton dissociation, which consequently contribute to photocurrent, indicating that the nanostructural characteristics at multiple length scales is one of the key factors determining the performance of PTB7 copolymer, and likely most polymer/fullerene systems, in OPV devices.
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