Photochemical stability of high efficiency PTB7:PC70BM solar cell blends
- 30 October 2014
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of Materials Chemistry A
- Vol. 2 (47), 20189-20195
- https://doi.org/10.1039/c4ta05641h
Abstract
Thieno[3,4 b]thiophene-alt-benzodithiophene (PTB7) is a promising donor–acceptor copolymer that has achieved high efficiencies (7–9%) in organic solar cells but suffers from poor stability and degrades when exposed to light and oxygen. Using resonant Raman spectroscopy to examine the nature of this photo-oxidation, three main changes to the vibrations of the conjugated backbone are observed: (1) shift of the benzodithiophene (BDT) CC stretch peak at ∼1489 cm−1 up to ∼1499 cm−1; (2) increase in the relative intensity of coupled fused thiophene and benzene CC stretch peaks at ∼1535 and ∼1575 cm−1; (3) appearance of a new peak at ∼1650 cm−1; which suggest oxidation takes place on the BDT unit without loss of conjugation. In situ accelerated photo-degradation reveals that the observed oxidation is the initial step of degradation, which is followed by reductions in absorption and Raman scattering intensities that indicate the loss of chromophores by a second, more extensive oxidation step. Blending PTB7 with PC70BM is found to accelerate the polymer's degradation, and further shift the BDT peak to ∼1509 cm−1. Using density functional theory to simulate Raman spectra for several possible oxidised products, the initial oxidation is best described by hydroxylation of 3rd and 7th positions on the BDT donor unit.Keywords
Funding Information
- Engineering and Physical Sciences Research Council (EP/G037515/1)
This publication has 21 references indexed in Scilit:
- Enhanced power-conversion efficiency in polymer solar cells using an inverted device structureNature Photonics, 2012
- Stability of Polymer Solar CellsAdvanced Materials, 2011
- Economic assessment of solar electricity production from organic-based photovoltaic modules in a domestic environmentEnergy & Environmental Science, 2011
- Towards sustainable photovoltaics: the search for new materialsPhilosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2011
- Degradation and stabilization of poly(3-hexylthiophene) thin films for photovoltaic applicationsPolymer Bulletin, 2010
- Stability/degradation of polymer solar cellsSolar Energy Materials and Solar Cells, 2008
- Pathways for the degradation of organic photovoltaic P3HT:PCBM based devicesSolar Energy Materials and Solar Cells, 2008
- A brief history of the development of organic and polymeric photovoltaicsSolar Energy Materials and Solar Cells, 2004
- Organic photovoltaics: technology and marketSolar Energy Materials and Solar Cells, 2004
- Organic Solar CellsAdvanced Materials, 1991