Hydrophobicity Control in Adaptive Crystalline Assemblies.

An amphiphile based on polyethylene glycol (PEG) polymer and two molecular moieties (perylene diimide and C7 fluoroalkyl, PDI and C7 F) attached to its termini assembles into crystalline films with long-range order. The films reversibly switch from crystalline to amorphous above the PEG melting temperature. The adaptive behavior stems from the responsiveness of the PEG domain and the robustness of the PDI and C7 F assemblies. The hydrophobicity of the film can be controlled by heating, resulting in switching from highly hydrophobic to superhydrophilic. The long-range order, reversible crystallinity switching, and the temperature-controlled wettability demonstrate the potential of block copolymer analogues based on simple polymeric/molecular hybrids.

A-Site Cation Dependence of Self-Healing in Polycrystalline APbI3 Perovskite Films.

In terms of sustainable use, halide perovskite (HaP) semiconductors have a strong advantage over most other classes of materials for (opto)electronics, as they can self-heal (SH) from photodamage. While there is considerable literature on SH in devices, where it may not be clear exactly where damage and SH occur, there is much less on the HaP material itself. Here we perform "fluorescence recovery after photobleaching" (FRAP) measurements to study SH on polycrystalline thin films for which encapsulation is critical to achieving complete and fast self-healing. We compare SH in three photoactive APbI3 perovskite films by varying the A-site cation ranging from (relatively) small inorganic Cs through medium-sized MA to large FA (the last two are organic cations). While the A cation is often considered electronically relatively inactive, it significantly affects both SH kinetics and the threshold for photodamage. The SH kinetics are markedly faster for γ-CsPbI3 and α-FAPbI3 than for MAPbI3. Furthermore, γ-CsPbI3 exhibits an intricate interplay between photoinduced darkening and brightening. We suggest possible explanations for the observed differences in SH behavior. This study's results are essential for identifying absorber materials that can regain intrinsic, insolation-induced photodamage-linked efficiency loss during its rest cycles, thus enabling applications such as autonomously sustainable electronics.

Remanent Polarization and Strong Photoluminescence Modulation by an External Electric Field in Epitaxial CsPbBr3 Nanowires.

Metal halide perovskites (MHPs) have unique characteristics and hold great potential for next-generation optoelectronic technologies. Recently, the importance of lattice strain in MHPs has been gaining recognition as a significant optimization parameter for device performance. While the effect of strain on the fundamental properties of MHPs has been at the center of interest, its combined effect with an external electric field has been largely overlooked. Here we perform an electric-field-dependent photoluminescence study on heteroepitaxially strained surface-guided CsPbBr3 nanowires. We reveal an unexpected strong linear dependence of the photoluminescence intensity on the alternating field amplitude, stemming from an induced internal dipole. Using low-frequency polarized-Raman spectroscopy, we reveal structural modifications in the nanowires under an external field, associated with the observed polarity. These results reflect the important interplay between strain and an external field in MHPs and offer opportunities for the design of MHP-based optoelectronic nanodevices.