Ultrafast photophysics of π-conjugated polymers for organic photovoltaic applications

Publication Type dissertation
School or College College of Science
Department Physics & Astronomy
Author Chhetri, Bill Pandit
Title Ultrafast photophysics of π-conjugated polymers for organic photovoltaic applications
Date 2012-08
Description In this work, we used the pump-probe photomodulation (PM) spectroscopy technique to measure the transient PM spectrum and decay kinetics in various π - conjugated polymers (PCPs) films and blends with appropriate molecular acceptors. Using two ultrafast laser systems, we covered a broad spectral range from 0.25 - 2.5 eV in the time domain from 100 fs to 1 ns with 150 fs time resolution. We also used continuous wave (CW) photomodulation spectroscopy, photoluminescence, electro-absorption, doping-induced absorption, and x-ray diffraction to study the excitations and other optical properties of PCPs and polymer donor-fullerene acceptor blends. In P3HT/PCBM blend with maximum domain separation we found that although the intrachain excitons in the polymer domains decay within ~ 10 ps, no charge polarons are generated at their expense. Instead, there is a build-up of charge-transfer (CT) excitons at the donor (D) - acceptor (A) interfaces that may dissociate into separated polarons in the D and A domains at a later time. Our results elucidate the charge photogeneration mechanism in polymer/fullerene blends, and unravel the important role of the binding energy in generating free charge polarons. We also studied the photophysics of a low band gap polymer, namely poly-thienophene-benzodithiophene seven (PTB7) film and its blend with acceptor [6,6] phenyl C71 butyric acid methyl ester [PC71BM]. In the CW PM spectrum of PTB7/PC71BM blend, clear signatures of polarons are observed. Whereas PA bands of triplet excitons and trapped polarons are observed in pristine PTB7 film. In the transient ultrafast PA spectrum of PTB7/PC71BM blend, surprisingly, we found singlet exciton, charge transfer exciton and a polaron band that are generated simultaneously; this is different from the transient PM spectrum of P3HT/PCBM blend. We also focused on the photophysics of DOO-PPV with different isotopes and their blends with PCBM. The transient ultrafast PA spectra of all isotope films are dominated by a singlet exciton. Similar results were observed in the isotope/PCBM blends. As in P3HT/PCBM blend, we do not observe the charge transfer exciton and polaron band immediately after photoexcitation, but they show up in the PM spectrum at a later time.
Type Text
Publisher University of Utah
Subject π-conjugated polymers; Ultrafast photophysics; Organic photovoltaic applications
Subject LCSH Conjugated polymers -- Optical properties; Photovoltaic power generation
Dissertation Institution University of Utah
Dissertation Name Doctor of Philosophy
Language eng
Rights Management Copyright © Bill Pandit Chhetri 2012
Format Medium application/pdf
Format Extent 3,416,594 bytes
Identifier etd3/id/1766
Source Original in Marriott Library Special Collections, QC3.5 2012 .C44
ARK ark:/87278/s6q24f2h
Setname ir_etd
Date Created 2012-08-02
Date Modified 2017-12-11
ID 195455
Reference URL https://collections.lib.utah.edu/details?id=195455
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