However, as is seen from Figure , both single and double exponential functions do not provide a satisfactory fit with our TRMC decay. In order to understand this better, we made double log plots of TRMC decays (Figure ). It is evident from the plots that there are different decay processes that begin at different times (a fast process occuring in less than 100 ns, and a slow process occuring beyond 15 μs). If the two processes began at the same time, then a double exponential function would fit well with our data. As this is clearly not the case, we treated these processes separately and fitted them each with a single exponential function, as shown in Figure c. This method leads to better fits of our TRMC decay, and the time constants of these processes (tfast and tslow) could be determined (Figure ). The initial fast decay is probably due to defectmediated recombination, which is also the decay process active under moderate stationary illumination, i.e. in PV and PEC devices under standard operational conditions. The difference in tfast between the Sb2Se3 and the sulfur-treated Sb2Se3 was found to decrease with increasing light intensity due to progressively dominant higher order recombination (Figure ). At the highest light intensities (>10 photons/cm 2 /pulse), the difference in lifetime between Sb2Se3 and sulfurtreated films was found to be minimal as a result of direct electron and hole recombination. The dependence of the decay time of this process on the excitation density (Figure ) is difficult to explain, although a defect-mediated recombination process can depend on the excitation density.