Enhancing the Stability of Orthorhombic CsSnI3 Perovskite via Oriented π-Conjugated Ligand Passivation

Stabilization of lead-free bulk CsSnI3 perovskite thermoelectrics via incorporation of TiS3 nanoribbon clusters

The intense research for efficient low-temperature thermoelectric materials drives the exploration of innovative compounds and composite systems. This study investigates the effects of integrating low-dimensional titanium trisulfide (TiS3) into bulk tin-based halide perovskites (CsSnI3) for thermoelectric applications. The incorporation of small amounts of two-dimensional titanium trisulfide (TiS3) into CsSnI3 not only significantly enhanced the structural stability of the composite material and suppressed oxidation processes but also ensured that its initial electrical properties, including conductivity and the Seebeck coefficient, remained stable for at least 24 hours-unlike the pristine CsSnI3 sample. These findings emphasize the potential of low-dimensional TiS3 as an effective additive for stabilizing the thermoelectric performance of CsSnI3-based materials over time.

Zwitterionic Carbazole Ligands Enhance the Stability and Performance of Perovskite Nanocrystals in Light-Emitting Diodes

We introduce a new carbazole-based zwitterionic ligand (DCzGPC) synthesized via Yamaguchi esterification which enhances the efficiency of lead halide perovskite (LHP) nanocrystals (NCs) in light-emitting diodes (LED). A facile ligand exchange of the native ligand shell, monitored by nuclear magnetic resonance (NMR), ultraviolet-visible (UV-vis), and photoluminescence (PL) spectroscopy, enables more stable and efficient LHP NCs. The improved stability is demonstrated in solution and solid-state LEDs, where the NCs exhibit prolonged luminescence lifetimes and improved luminance, respectively. These results represent a promising strategy to enhance the stability of LHP NCs and to tune their optoelectronic properties for further application in LEDs or solar cells.

Are formation and adsorption energies enough to evaluate the stability of surface-passivated tin-based halide perovskites?

Surface passivation is one of the effective and widely-used strategies to enhance the stability of halide perovskites with reduced surface defects and suppressed hysteresis. Among all existing reports, the formation and adsorption energies are popularly used as the decisive descriptors for screening passivators. Here, we propose that the often-ignored local surface structure should be another critically important factor governing the stability of tin-based perovskites after surface passivation, but has no detrimental effect on the stability of lead-based perovskites. It is verified that poor surface structure stability and deformation of the chemical bonding framework of Sn-I caused by surface passivation are ascribed to the weakened Sn-I bond strength and facilitated formation of surface iodine vacancy (V_I). Therefore, the surface structure stability represented by the formation energy of V_I and Sn-I bond strength should be used to accurately screen preferred surface passivators of tin-based perovskites.

Ultrafast Response of Centimeter Scale Thin CsPbBr3 Single Crystal Film Photodetector for Optical Communication

The photodetector (PD) is the key component to realize efficient optoelectronic conversion signal in the visible light communication (VLC) system. The response speed directly determines the bandwidth of the whole system. Metal halide perovskite is a neotype of low-cost solution processing semiconductor, with strong optical absorption, low trap density, and high carrier mobility, thus has been widely explored in photoelectric detection applications. However, previously reported perovskite polycrystalline photodetectors exhibit limited response speed due to the existence of grain boundaries. Here, an improved confined space method is developed through adjusting the heating area to control nucleation, resulting in centimeter scale fully inorganic perovskite CsPbBr₃ thin single crystal films (SCFs) (<40 µm). The smooth surface and high crystallinity of CsPbBr₃ SCFs render admirable exciton lifetime. The planar metal-semiconductor-metal photodetector using CsPbBr₃ SCF as the photosensitive layer demonstrates a limit response time of 200/300 ns and a VLC within 100-500 kHz frequency for both 365 nm and white light, which is superior to previously reported CsPbBr₃ polycrystalline film and single crystal photodetectors.

Effects of conjugated structure on electronic and transport properties in organic-inorganic hybrid superlattices Cd2Se2(C2H4N2)1/2

By inducingπ-conjugated organic molecule C₂H₄N₂in group II-VI based CdSe network structure materials, the band structures and carrier transport of organic-inorganic hybrid superlattices Cd₂Se₂(C₂H₄N₂)_1/2were investigated via first-principles calculations based on the density functional theory. With different stacking patterns, it is found that the carrier mobility can be modulated by 5-6 orders of magnitude. The physical mechanism of the high carrier mobility in the hybrid structures has been revealed, which means dipole organic layers realize electron delocalization via electrostatic potential difference and build-in electric field. Our calculations shown that the dipole organic layers originate from asymmetricπ-conjugated organic molecules and the charges movement between molecules, while symmetric organic molecules tend to electrostatic balance. And although the electronic transport properties were highly restrained by the flat bands of organic layers around Fermi energy in most structures, we found that the collective electrostatic effect can lead to very high electron mobility in AA1 and AA2 stacking systems, which might be attributed to the superposition of molecule electrostatic potential along with electrons transfer between molecules. Furthermore, it is also found that the anisotropy of electron mobility can be modulated via the difference directions of dipole layers.

The role of sodium in stabilizing tin-lead (Sn-Pb) alloyed perovskite quantum dots

Narrow-bandgap CsSn x Pb1-x I3 perovskite quantum dots (QDs) show great promise for optoelectronic applications owing to their reduced use of toxic Pb, improved phase stability, and tunable band gaps in the visible and near-infrared range. The use of small ions has been proven beneficial in enhancing the stability and photoluminescence quantum yield (PLQY) of perovskite QDs. The introduction of sodium (Na) has succeeded in boosting the PLQY of CsSn0.6Pb0.4I3 QDs. Unfortunately, the initial PLQY of the Na-doped QDs undergoes a fast degradation after one-day storage in solution, hindering their practical applications. Using density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations, we study the effect of Na ions on the strength of surface bonds, defect formation energies, and the interactions between surface ligands and perovskite QDs. Our results suggest that Na ions enhance the covalent bonding of surface tin-iodine bonds and form strong ionic bonding with the neighboring iodine anions, thus suppressing the formation of I and Sn vacancies. Furthermore, Na ions also enhance the binding strength of the surface ligands with the perovskite QD surface. However, according to our AIMD simulations, the enhanced surface ligand binding is only effective on a selected surface configuration. While the position of Na ions remains intact on a CsI-terminated surface, they diffuse vigorously on an MI2-terminated surface. As a result, the positive effect of Na vanishes with time, explaining the relatively short lifetime of the experimentally obtained high PLQYs. Our results indicate that engineering the surface termination of the QDs could be the next step in maintaining the favorable effect of Na doping for a high and stable PLQY of Sn-Pb QDs.