Fabio Candolfi

The inherent susceptibility of n‐type organic semiconductors to molecular dioxygen (O ₂ ) results in electron trapping or in unintended p‐doping, which in turn diminishes their electron mobility. This concept is challenged in the present study by exploring O ₂ interactions with organic charge‐transfer complexes (CTCs), where electron donor–acceptor interactions generate partially delocalized electronic states. Using a CTC comprising a phenazine electron donor and a 7,7,8,8‐tetracyanoquinodimethane (TCNQ) electron acceptor, we demonstrate that its exposure to O ₂ does not lead to electron extraction but instead enhances the charge‐transfer activity. The increased electron density at the TCNQ acceptor upon CTC exposure to O ₂ is attributed to electron trap‐states passivation by O ₂ , without evidence of chemisorption. This passivation mitigates recombination losses, resulting in a threefold photoluminescence quantum yield increase, enhanced electrical conductivity, and improved charge‐transfer state efficiency. Similar O ₂ ‐mediated conductivity enhancements are observed across additional donor–acceptor pairs, proving the broader applicability of this effect, and paving the way for designing O ₂ ‐enhanced advanced organic electronic materials.

When annealing a 4H silicon carbide (SiC) crystal, a sequence of optically active defect centers occurs among which the TS center is a prominent example. Here, we present low-temperature photoluminescence analyses on the single defect level. They reveal that the three occurring spectral signatures TS1, TS2 and TS3 originate from one single defect. Their polarization dependences expose three different crystallographic orientations in the basal plane, which relate to the projections of the nearest neighbor directions. Accordingly, we find a three-fold level-splitting in ensemble studies, when applying mechanical strain. This dependency is quantitatively calibrated. A complementary electrical measurement, deep level transient spectroscopy, reveals a charge transition level of the TS defect at 0.6 eV above the valence band. For a future identification, this accurate characterization of its optical and electronic properties along with their response to mechanical strain is a milestone.