We investigate the EMAS spectra of PbS-A on an IHO working electrode in TBAHFP/MeCN-d 3 in the oxidative direction in . We follow the former interpretation, mainly due to a larger uncertainty in determining the 1/8 ΔA-level against the background in our data. We observe the formation of a bleach of the 1S h -1S e transition (1470 nm) at -0.05 V vs. Fc/Fc + . The bleach of the 1P h -1P e transition (1050 nm) commences at approx. 0.0 V. Upon continuation to more oxidative potentials (and longer time in the electrolyte), the bleach shifts to shorter wavelengths until it saturates at 1350 nm. Resetting the potential to the open circuit potential and repeating the measurement results in a bleach at the new, shorter wavelength, indicating that the spectral shift is permanent (see Figure ). We find a similar behaviour for the bleach of the 1P h -1P e transition, which shifts to 950 nm. The intensity of the 1S h -1S e bleach exhibits a maximum, and the bleaches observed in repeated measurements of the same sample are generally weaker. We display the corresponding EMAS results of the reductive direction in Figure . The line cuts at selected wavelengths in Figure exhibit an inflection point at approx. -0.85 V for the modulation of the 1S h -1S e and the 1P h -1P e transitions, but their ΔA-values are now positive, that is, they constitute induced absorptions. Consistent with the oxidative EMAS results, we observe shifts of the ΔA-maxima to roughly 1350 nm and 950 nm, respectively. Control experiments with PbS-B to PbS-D lead to similar results (see Figures ), only at slightly different potentials. Most notably, we find the general hypsochromic spectral shift and the induced absorption in the reductive scan direction in all EMAS measurements of PbS samples on IHO. Changing the electrolyte to LiClO 4 /MeCN-d 3 results in comparable EMAS spectra (Figure ). We summarize the complete EMAS results for PbS-A to PbS-D in both scan directions in Figure . Red colour indicates negative ΔA, while blue colour represents an induced absorption. The horizontal dashed lines mark the respective potentials at which 50% of the maximum ΔA is reached as determined by the inflection points in their linecuts at the wavelength of the excitonic transition. The vertical lines refer to characteristic transitions (e.g. 1S h -1S e and 1P h -1P e ) and are referenced to the second derivative of the corresponding absorption spectra from Figure . For PbS-A, we find a clean bandgap of roughly 0.8 eV, in accordance with the optical bandgap obtained by absorption spectroscopy. The inflection points for the positive (-0.05 V) and negative scan direction (-0.85 V) are largely consistent with Figure and Figure . In contrast to the DPV results (Figure ), there is no significant signal around -0.5 V, suggesting that this redox wave originated from an impurity not related to PbS. This emphasizes the power of spectroelectrochemistry with the ability to differentiate between such signals of different origin. For PbS-B, we note overall similar EMAS results, however with some significant in-gap density of states, in particular near the valence band edge. Taking -0.70 V and +0.05 V as the inflection points of the conduction and valence band, respectively, (see Figure for details) suggests an Urbach-like tailing into the bandgap of approx. 250 meV from the valence band, which compares to less than 100 meV in the case of PbS-A. While it is unclear to which extent this result reflects the broader excitonic feature for PbS-B vs. PbS-A (see Figure ) or a larger density of trap states, it emphasizes that EMAS can illustrate such samplespecific properties. For PbS-C and PbS-D, the inflection points are at -0.8 V/+0.20 V and -0.65 V/+0.20 V, respectively (Figures S10+S11), overestimating the optical bandgap by 0.25 eV and 0.13 eV. This appears to be the consequence of a relatively broad density of states in the vicinity of the band edges (particularly for PbS-C) that can even lead to a sign flip of the EMAS signal, rendering a precise determination of the inflection point challenging. A direct comparison of all EMAS spectra illustrates a consistent spectral shift in accordance with the different excitonic transition wavelengths for both scan directions (Figure ).