Preferential Charge Generation at Aggregate Sites in Narrow Band Gap Infrared Photoresponsive Polymer Semiconductors
Abstract
Infrared organic photodetector materials are investigated using transient absorption spectroscopy, demonstrating that ultrafast charge generation assisted by polymer aggregation is essential to compensate for the energy gap law, which dictates that excited state lifetimes decrease as the band gap narrows. Short sub‐picosecond singlet exciton lifetimes are measured in a structurally related series of infrared‐absorbing copolymers that consist of alternating cyclopentadithiophene electron‐rich “push” units and strong electron‐deficient “pull” units, including benzothiadiazole, benzoselenadiazole, pyridalselenadiazole, or thiadiazoloquinoxaline. While the ultrafast lifetimes of excitons localized on individual polymer chains suggest that charge carrier generation will be inefficient, high detectivity for polymer:PC71BM infrared photodetectors is measured in the 0.6 71BM films. In these blends, charge carriers form primarily at polymer aggregate sites on the ultrafast time scale (within our instrument response), leaving quickly decaying single‐chain excitons unquenched. The results have important implications for the further development of organic infrared optoelectronic devices, where targeting processes such as excited state delocalization over aggregates may be necessary to mitigate losses to ultrafast exciton decay as materials with even lower band gaps are developed.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Feb 13, 2018
- Source ID
- 10.1002/adom.201701138
Entities
People
- Alexander E. London
- Bryan M. Wong
- Cody W. Schlenker
- Dana B. Sulas
- Jason D Azoulay
- Lifeng Huang
- Lihua Xu
- Matthew Sfeir
- Tse Nga Ng
- Zhenghui Wu
Organizations
- Air Force Office of Scientific Research
- Brookhaven National Laboratory
- National Science Foundation
- United States Department of Energy
- University of California, Riverside
- University of California, San Diego
- University of Southern Mississippi
- University of Washington