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Photodegradation of C‐PCPDTBT and Si‐PCPDTBT: Influence of the Bridging Atom on the Stability of a Low‐Band‐Gap Polymer for Solar Cell Application
Author(s) -
Aygül Umut,
Egelhaaf HansJoachim,
Nagel Peter,
Merz Michael,
Schuppler Stefan,
Eichele Klaus,
Peisert Heiko,
Chassé Thomas
Publication year - 2015
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201402494
Subject(s) - x ray photoelectron spectroscopy , photodegradation , materials science , polymer , band gap , reactivity (psychology) , spectroscopy , kinetics , photochemistry , chemistry , chemical engineering , organic chemistry , catalysis , photocatalysis , physics , optoelectronics , medicine , alternative medicine , pathology , quantum mechanics , engineering , composite material
Abstract The kinetics of photodegradation and the reactivity of different sites of the low‐band‐gap polymers poly[2,6‐(4,4‐ bis ‐(2‐ethylhexyl)‐4 H ‐cyclopenta[2,1‐ b :3,4‐ b ′]dithiophene)‐ alt ‐4,7‐(2,1,3‐benzothiadiazole)] (C‐PCPDTBT) and poly[2,6‐(4,4‐ bis ‐(2‐ethylhexyl)dithieno[3,2‐ b :2′,3′‐ d ]silole)‐ alt ‐4,7‐(2,1,3‐benzothiadiazole)] (Si‐PCPDTBT) are investigated as thin films and are compared to those of poly(3‐hexylthiophene) (P3HT). The decay kinetics are monitored with UV/Vis spectroscopy and the reactivity and product evolution are investigated with X‐ray photoelectron spectroscopy (XPS). Both polymers exhibit higher stability than P3HT. The bridging atom in the cyclopentadithiophene (CPDT) subunit has a significant influence on the stability. Varying oxidation rates for the different elements were observed. In the case of Si‐PCPDTBT, the silicon atom is oxidized primarily, whereas the photooxidation rates of the other elements are reduced relative to C‐PCPDTBT. Additionally, XPS experiments with varying excitation energies reveal a significant reaction gradient within a few nanometers of the surface of degraded thin films of C‐PCPDTBT.