Interesting to note is the fact that at a relatively low intensity of photons from the laser (~10 photons/cm 2 per pulse) clear TRMC signals could be detected in contrast to the light intensities of >10 photons/cm 2 /pulse that are needed to detect signals from many other absorber materials. This observation reveals the excellent optoelectronic properties and low trap density of Sb2Se3. The maximum of the (non-normalized) peak height is quite similar for the two different sample types showing that the sulfur treatment did not substantially change the effective mobility values of the charge carriers. The charge carriers generated are proportional to the incident light intensity on the semiconductor, and the recombination of charge carriers can be understood using the general recombination rate equation given by 𝑑𝑑𝑑𝑑 𝑑𝑑𝑑𝑑 = -𝑎𝑎𝑑𝑑 -𝑏𝑏𝑑𝑑 ' -𝑐𝑐𝑑𝑑 where n is the photocarrier density, and a, b, and c are recombination rate constants. If the change in photocarrier density dn/dt (controlled by a change in incident light intensity) shows a linear dependence, then first order recombination is the dominant recombination process (i.e., a » 1 and b,c << 1), while a sub-linear dependence would indicate higher order recombination processes.