Wavelength-Dependent Pathways of Poly-3-hexylthiophene Photo-Oxidation

Abstract

The photodegradation kinetics of regioregular poly-3-hexylthiophene (P3HT) thin films (∼150 nm) upon illumination with both visible light of 525 nm and UV light of 365 nm has been studied using UV/vis and FTIR spectroscopy in order to probe both the disruption of the π-conjugated system and the chemical product evolution. Reaction effectiveness and product evolution turn out to depend strongly on the wavelength of the incident light. Under UV light, the π-conjugated system and the hexyl side chain are degraded almost simultaneously, involving Norrish-type reactions that lead to complete disintegration of the alkyl chains. Under visible light only the π-conjugated system is destroyed, whereas the aliphatic side chains are hardly affected. While the reaction under UV light is consistent with a radical reaction starting at the α-carbon of the alkyl side chain, the reaction under visible illumination is more likely to involve a photosensitized species that primarily attacks the π-conjugated system of the polymer.

Wavelength influence on the photodegradation of P3HT:PCBM organic solar cells

“…Restricting our discussion to those mechanisms, it is generally accepted that UV radiation is able to promote physical or chemical degradation in polymeric materials, as this energy could be enough to break chemical bonds [37][38][39]. Although the threshold photon energy to break chemical bonds could differ for different polymers, as a general rule deeper degradation from UV photons might be expected, in agreement to our results.…”

“…Although the threshold photon energy to break chemical bonds could differ for different polymers, as a general rule deeper degradation from UV photons might be expected, in agreement to our results. Hintz et al [39] reported the photodegradation of P3HT upon illumination with both visible (525 nm) and UV (365 nm) light, finding that the degradation products depend strongly on the wavelength of the incident light. For UV irradiation the π-conjugated system and the hexyl side chain are degraded simultaneously, while for visible light only the π-conjugated system is affected.…”

FTIR Study of the Impact of PC[60]BM on the Photodegradation of the Low Band Gap Polymer PCPDTBT under O2 Environment

“…7,8,16,[20][21][22] In these polymers, the photo-oxidation process seems to follow a radical chain based mechanism, which probably starts on the α-carbon atoms of the alkyl chains. 8,21 The addition of PCBM to films of these polymers results in decreased degradation rates, probably due to the radical scavenging effect of the fullerene.…”

Photodegradation of Si-PCPDTBT:PCBM active layer for organic solar cells applications: A surface and bulk investigation

“…[9,10,12,13,16,19] The assignment of the different vibrational modes has been done by a direct comparison with the spectra of pure PC 70 BM and Si-PCPDTBT:PC 70 BM. (Fig.…”