Heterojunctions underpin the design and performance of virtually all devices based on conventional semiconductors. While metal halide perovskites have received intense attention for applications in photoconversion and optoelectronics, these devices are often hybrid, containing interfaces between the perovskite and metal oxide or organic semiconductor layers. Heterojunctions between two perovskite layers could enable new paradigms in device engineering, but to date, their formation has remained limited due to difficulty in fabricating multilayers and facile ion diffusion across interfaces. Here, sequential solution and vapor processing is used to successfully fabricate perovskite/perovskite heterojunctions comprising three-dimensional APbX 3 /CH 3 NH 3 SnX 3 [A = CH(NH 2 ) 2 , CH 3 NH 3 , or Cs; X = I or Br] layers. Heterojunction stability is investigated leading to the identification of two pairings that are stable for >1500 h at room temperature. By probing mixing as a function of composition and grain size, we propose general design rules for the realization of stable perovskite/perovskite heterojunctions.

Zeolites are strongly hydrophilic materials that are widely used as water adsorbents. They are also promising candidates for antifogging coatings; however, researchers have yet to devise a suitable method for coating glass substrates with zeolite-based films. Here, we report on a direct wet deposition technique that is capable of casting zeolite films on glass substrates without exposing the glass to highly basic solutions or the vapors used in zeolite synthesis. We began by preparing cast solutions of pure silica zeolite MFI synthesized in hydrothermal reactions of various durations. The solutions were then applied to glass substrates via spin-on deposition to form zeolite films. The resulting zeolite MFI thin films were characterized in terms of transmittance to visible light, surface topography, thin film morphology, and crystallinity. Wetting and antifogging properties were also probed. We found that hydrophilicity and antifogging capability increased with the degree of thin film crystallinity. We also determined that the presence of the amorphous silica in the thin films is critical to transparency. Fabricating high-performance zeolite-based antifogging coatings requires an appropriate composition of zeolite crystals and amorphous silica.

Zeolites are microporous crystalline materials widely used in catalysis and adsorption applications. The fabrication of zeolite thin films and membranes has also opened up the possibility of using zeolites in electronic devices and membrane separations. The existing approach to growing zeolite films involves exposing the substrate to a high-pH environment; however, this process is applicable to only specific types of substrates. Our group has developed the direct wet deposition of zeolites via ultrasonic nozzle spray deposition to address this issue; however, the relationship between wetting properties and thin-film quality has yet to be investigated. In this study, we prepared zeolite CHA (Si:Al:P = 3:10:20) suspensions using different solvents and surfactants in various concentrations. We then examined the relationships among the composition of the cast solution, their wetting behavior on the glass substrate, and the uniformity of the resulting thin films. We found that using ethanol as a solvent with zeolite crystals in low concentrations with added surfactant yielded zeolite films of high quality. We were also able to produce low-haze zeolite coatings on glass. The zeolite coatings with high hydrophilicity and adsorption capacity presented excellent antifogging capability.

High-performance antifog coatings are critical for devices operating in high-humidity environments, such as endoscopes. However, existing antifog coatings have been unable to achieve good antifogging capability with low haze, uniform color, and high durability. The relationships between the properties of the cast solution and the quality of the resulting coatings remain unclear. This work was aimed to investigate the spreading dynamics of zeolite cast solutions on a glass substrate to elucidate the relationship between the wetting behavior and thin-film quality, as quantified by transmittance and haze. The fundamental understanding will lead to the development of highly stable zeolite-based antifog coatings with low haze and free from the interference effect. We used direct wet deposition to coat a glass substrate with a layer of pure-silica zeolite MFI, whose surface had a silanol density. The solvent and composition of the zeolite suspensions were varied with the aim of optimizing the uniformity of the coating. We found that the bulk transmittance and haze of the coating were dominantly controlled by the packing of zeolite particles at the micrometer scale, which was affected by the wetting property of the cast solution on the substrate. Our results demonstrated that long-lasting low-haze antifog coatings can be produced from pure-silica zeolite MFI suspended in ethanol in the absence of amorphous silica colloids.