Fluorescence Lifetime Measurement using Time Correlated Single Photon Counting

Abstract: A time correlated single photon counting (TCSPC) setup is built to measure the fluorescence decay of samples, such as solar cell materials. TCSPC is a sensitive technique for measuring fluorescence decays on nanosecond time scale and longer. The principle of TCSPC is based on the precise registration of the arrival time of fluorescence photons from a sample. A fluorescence decay curve is constructed from the TCSPC measurement, this curve is used to extract the fluorescence lifetime. The setup is novel with respect to the conventional method of collecting a fluorescence signal. It is a simplified setup as there is no need of complex geometry of optics to focus the excitation beam or to image the fluorescence on to the detector. Instead, the excitation beam is unfocused and the sample is placed as close to the detector as possible. This approach allows for the usage of low excitation density of photons. The low level of light that this setup could detect made it very sensitive for measuring samples with low emission. The setup is characterised with two different samples: Coumarin-152 (7-N,N-dimethylamino-4-trifluoromethyl-1,2-benzopyrone) and APFO3 (poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(4,7′-di-2-thienyl-2′,1′,3- benzothiadiazole)]). Coumarin-152 is a commercial laser dye and APFO3 is a polymer solar cell material. These measurements reveal that the single and non exponential curves could be obtained using this setup. The verification of the setup is further carried out by classifying different errors that can influence the measurements.