Absolute photoluminescence quantum efficiency of P3HT/CHCl3 solution by Thermal Lens Spectrometry

Thermal Lens Spectrometry (TLS), as well as all photothermal methods, rely on the determination of the fraction of absorbed energy converted in heat (φ), which in turn is related to photoluminescence quantum efficiency (η). In this study, we have used TLS to measure η of Poly(3-hexylthiophene) (P3HT) dissolved in chloroform as a function of concentration and excitation wavelength. For samples synthesized by oxidative polymerization (∼74% HT content), η = 0.39 ± 0.02 was found to be constant with excitation energy (UV–vis, 335–514 nm) and concentration, from 10−4 to 0.6 mg/mL. The value of η was practically the same as that of a commercial regioregular P3HT (>95% HT content), measured under the same conditions. The photodegradation effect was also quantitatively analyzed. Although the average emission wavelength of the photo-degraded sample depends on excitation wavelength, both φ and η are constant in the UV–vis range.