Layer-dependent optical and dielectric properties of centimeter-scale PdSe2 films grown by chemical vapor deposition

Palladium diselenide (PdSe2), a new type of two-dimensional noble metal dihalides (NMDCs), has received widespread attention for its excellent electrical and optoelectronic properties. Herein, high-quality continuous centimeter-scale PdSe2 films with layers in the range of 3L–15L were grown using Chemical Vapor Deposition (CVD) method. The absorption spectra and DFT calculations revealed that the bandgap of the PdSe2 films decreased with the increasing number of layers, which is due to the enhancement of orbital hybridization. Spectroscopic ellipsometry (SE) analysis shows that PdSe2 has significant layer-dependent optical and dielectric properties. This is mainly due to the unique strong exciton effect of the thin PdSe2 film in the UV band. In particular, the effect of temperature on the optical properties of PdSe2 films was also observed, and the thermo-optical coefficients of PdSe2 films with the different number of layers were calculated. This study provides fundamental guidance for the fabrication and optimization of PdSe2-based optoelectronic devices.

Photo de-mixing in mixed halide perovskites: the roles of ions and electrons

Mixed halide perovskites have attracted great interest for applications in solar cells, light emitting diodes and other optoelectronic devices due to their tunability of optical properties. However, these mixtures tend to undergo de-mixing into separate phases when exposed to light, which compromises their operational reliability in devices (photo de-mixing). Several models have been proposed to elucidate the origin of the photo de-mixing process, including the contribution of strain, electronic carrier stabilization due to composition dependent electronic energies, and light induced ionic defect formation. In this perspective we discuss these hypotheses and focus on the importance of investigating defect chemical and ion transport aspects in these systems. We discuss possible optoionic effects that can contribute to the driving force of de-mixing and should therefore be considered in the overall energy balance of the process. These effects include the selective self-trapping of photo-generated holes as well as scenarios involving multiple defects. This perspective provides new insights into the origin of photo de-mixing from a defect chemistry point of view, raising open questions and opportunities related to the phase behavior of mixed halide perovskites.

Precrystalline P3HT nanowires: growth-controllable solution processing and effective molecular packing transfer to thin-film

Solution-processable precrystalline nanowires (NWs) of conjugated polymers (CPs) have garnered significant attention in fundamental research based on crystallization-driven self-assembly and in the roll-to-roll fabrication of optoelectronic devices such as organic...

Tunable band gap of layered semiconductor Zn3In2S6 under pressure

Band gap is an important property of a semiconductor, and a candidate material with highly tunable band gap under external tuning parameters will offer wider applications in optoelectronic devices and...