No conclusions can be (easily) drawn from the EDX maps based on the Cl K and N K fluorescence measured on the same sample spot as show in Figure 1a Figure 1a in the manuscript.

Metal oxides are considered as stable and low‐cost photoelectrode candidates for hydrogen production by photoelectrochemical solar water splitting. However, their power conversion efficiencies usually suffer from poor transport of photogenerated charge carriers, which has been attributed previously to a variety of effects occurring on different time and length scales. In search for common understanding and for a better photo‐conducting metal oxide photoabsorber, CuFeO2, α‐SnWO4, BaSnO3, FeVO4, CuBi2O4, α‐Fe2O3, and BiVO4 are compared. Their kinetics of thermalization, trapping, localization, and recombination are monitored continuously 100 fs–100 µs and mobilities are determined for different probing lengths by combined time‐resolved terahertz and microwave spectroscopy. As common issue, we find small mobilities < 3 cm2V‐1s‐1. Partial carrier localization further slows carrier diffusion beyond localization lengths of 1–6 nm and explains the extraordinarily long conductivity tails, which should not be taken as a sign of long diffusion lengths. For CuFeO2, the localization is attributed to electrostatic barriers that enclose the crystallographic domains. The most promising novel material is BaSnO3, which exhibits the highest mobility after reducing carrier localization by annealing in H2. Such overcoming of carrier localization should be an objective of future efforts to enhance charge transport in metal oxides.

Spectral dependent charge separation was investigated by modulated surface photovoltage (SPV) on layer systems with local contacts between CH3NH3PbI3 and PEDOT:PSS mixed with carboxylated multiwalled carbon nanotubes (MWCNT-COOH). In-phase SPV signals changed the sign with increasing amount of MWCNT-COOH in the PEDOT:PSS whereas the spectra could be approximated by a superposition of the spectra obtained for pure PEDOT:PSS and for PEDOT:PSS with 1.6 wt % of MWCNT-COOH. This was not the case for the control sample with pristine MWCNT. For a complex of a single-walled CNT-COOH (SWCNT-COOH) with a perovskite particle, density functional theory calculations showed an electron transfer to the perovskite which was not the case for a pristine SWCNT. Therefore, the transfer of electrons from MWCNT-COOH into illuminated CH3NH3PbI3 dominates fast separation of photogenerated charge carriers at local contacts with MWCNT-COOH.

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The present work comprises a practical tutorial on the topic of correlative microscopy and its application to optoelectronic semiconductor materials and devices. For the assessment of microscopic structure–property relationships, correlative electron microscopy, combined also with scanning-probe and light microscopy, exhibits a collection of indispensable tools to analyze various material and device properties. This Tutorial describes not only the various microscopy methods but also the specimen preparation in detail. Moreover, it is shown that electron microscopy can serve to monitor phase segregation processes on various length scales in semiconductor nanoparticles and thin films. Algorithms used to extract phase information from high-resolution transmission electron micrographs are explained.