Photodegradation of P3HT−A Systematic Study of Environmental Factors

Abstract

The influence of environmental factors on the degradation process of P3HT film has been investigated quantitatively. The decay kinetics of the polymer absorption during variation of intensity and spectral distribution of the incident light, oxygen concentration, humidity level as well as temperature are monitored using infrared and UV/vis absorption spectroscopy. Additionally, the oxygen diffusion into the polymer film has been investigated using fluorescence spectroscopy under the same experimental conditions. The degradation process is light initiated with a strong increase of the effectiveness toward the ultraviolet region of the spectrum. The observed photo oxidation is not oxygen diffusion limited although an activation energy of 26 kJmol -1 was observed for both degradation and oxygen diffusion. The observed kinetics, especially its dependence on wavelength of the incident light, point to a radical-based degradation process in the solid state rather than a singlet oxygen-based mechanism as it is observed in the liquid phase. Furthermore the presence of humidity strongly affects the degradation process although water itself does not decompose the polymer. Changing the structure of the polymer from regioregular to regiorandom significantly accelerates the degradation, probably due to the higher triplet yield of the regiorandom polymer.

Morphology and photochemical stability of P3HT:PCBM active layers of organic solar cells

“…Such an influence of the microstructure was also reported upon photooxidation experiments [24]. Changing the structure of the polymer from regioregular to regiorandom was shown to significantly increase the photooxidation rate by a factor 5 [24].…”

“…Changing the structure of the polymer from regioregular to regiorandom was shown to significantly increase the photooxidation rate by a factor 5 [24]. Concerning BA02, AL02 and RE, we showed that the photooxidation rate of RE is the double of BA02 and AL02…”

“…The absorbance at the initial maximum (552 nm for BA02 and AL02, 520 nm for RE) showed a linear decrease during the initial phase of the photodegradation. The degradation rate was determined as the initial slope of the curve A = f(t) (the concentration was obtained taking into account a thickness of 150 nm and an extinction coefficient of the thiophene unit ε =10 4 M -1 cm -1 [24]). The photodegradation rates (mol cm -3 h -1 ) of the three samples are reported in Table 2.…”

“…Upon photooxidative experiments, it was suggested that this effect could be related to the higher triplet yield of the regiorandom polymer, a possible pathway being the sensitization of singlet oxygen [24], meanwhile it has been shown that P3HT films are not attack by singlet oxygen [25]. This kind of explanation is not relevant under irradiation in the absence of oxygen.…”

Photoinduced p‐ to n‐type Switching in Thermoelectric Polymer‐Carbon Nanotube Composites

“…Photodegradation of P3HT in thin fi lms has indeed been well studied. [ 47,48 ] Photobleaching has been observed with an additional blueshift of the absorption associated to an ozone mediated decrease of the average length of π-conjugation. [ 49 ] In solution, on the other hand, the blueshift is not necessarily caused by ozone, but simple UV irradiation in an oxygen containing atmosphere is already suffi cient.…”