Indium phosphide (InP) quantum dots (QDs) are promising heavy-metal-free materials for optoelectronics, but their redox stability, trap-state landscape, and charge carrier dynamics are not well understood. Here we investigate InP and InP/ZnSe/ZnS QD films with different ligands by using spectroelectrochemistry. For both core-only and core/shell/shell QD films, the absorption spectra remain unchanged during charging, indicating that injected charges do not populate the conduction or valence bands. InP/ZnSe/ZnS QD films with original ligands exhibit reversible photoluminescence (PL) modulation: an increase at modest cathodic potentials, followed by quenching at more negative potentials. Solid-state ligand exchange using ethylenediamine (2DA) and sodium sulfide (Na₂S) enhances conductivity and induces stronger PL changes at both cathodic and anodic potentials. These results are in line with the population of electron traps at modest cathodic potentials (i.e., near the midbandgap), suppressing nonradiative recombination and increasing the PL. At more negative potentials, electrochemical reactions of surface species result in new trap states quenching the PL. Our findings provide insights into the stability and trap-state-mediated carrier dynamics during electrochemical charging of InP-based QDs. ... Read more

To boost the efficiency of perovskite solar cells beyond the limit of a single-junction cell, tandem cells are employed, requiring low bandgap materials. This is realized by partially substituting lead(II) (Pb2+) with tin(II) (Sn2+) in the perovskite structure. In this work, a scalable method is presented to produce formamidinium lead tin iodide (FAPb0.5Sn0.5I3) films by sequential thermal evaporation (sTE) of PbSnI4, which is an alloy of SnI2 and PbI2, and FAI, in vacuum. Annealing at 200 °C yields a highly oriented and crystalline layer comprising grains over 1 µm on average. Photoconductance measurements reveal carrier lifetimes exceeding 2 µs and mobilities ≈100 cm2/(Vs). Structural analysis confirms that, while interdiffusion is abundant even at room temperature, the complete conversion requires high temperatures. Although the incorporation of Cs+ into the A-site of the perovskite increases the grain size, charge carrier dynamics are reduced. A comparison between the sTE films and spin-coated samples of the same composition demonstrates the superior photoconductance of the sTE films, without the need for any additives. Overall, this study showcases the potential of sTE for producing high-quality low band gap (LBG) perovskite materials. ... Read more