Electrochemical Determination of the Ionization Energy and the Electron Affinity of Lead Halide Perovskite Thin Films: A Comparison to Ultraviolet Photoelectron Spectroscopy.

Reliable determination of ionization energies (IE) and electron affinities (EA) is essential for understanding energy-level alignment in solar cells. Here, we benchmark cyclic voltammetry (CV) and electrochemical voltage spectroscopy (EVS) for IE and EA determination against ultraviolet photoelectron spectroscopy (UPS) for IE and the combination of UPS and photothermal deflection spectroscopy (PDS) for EA. The investigated materials are FA 0.8 Cs 0.2 Pb ( I 1 - y Br y ) 3 perovskite thin films with varying bromide fraction y = 0-1. Onset potentials and energies were reproducibly extracted using tangent-based scripts, avoiding data smoothing and minimizing user bias. The optical band gap scales linearly with bromide fraction. The IE remains approximately constant up to y = 0.4 (EVS) and y = 0.6 (CV), increasing upon further substitution. All investigated methods consistently reveal a decrease in EA with increasing bromide content. Finally, we highlight practical considerations relevant to the application of EC methods and UPS.