Recognizing and correcting for errors in frequency-dependent modulation spectroscopy

This work shows how to acquire reliable data from frequency dependent continuous-wave modulation spectroscopy. We demonstrate this through the example of continuous-wave photoinduced absorption (cwPA), a characterization technique useful for studying long-lived photoexcitations in thin-film solar cell materials. Experimental errors arising at moderate frequencies in modulation spectroscopy are identified and corrected for. Limitations of the detectors and electronics are seen to cause both signal loss and phase shifts. Imperfect charge collection in the detector leads to wavelength-dependent correction factors, while phase shifts caused by the experimental setup call for frequency-dependent corrections. The methods outlined in this work act as a guide to avoid pitfalls in setting up modulation spectroscopy measurements and correcting for limitations.