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The next-generation semiconductors and devices, such as halide perovskites and flexible electronics, are extremely sensitive to water, thus demanding highly effective protection that not only seals out water in all forms (vapor, droplet, and ice), but simultaneously provides mechanical flexibility, durability, transparency, and self-cleaning. Although various solid-state encapsulation methods have been developed, no strategy is available that can fully meet all the above requirements. Here, we report a bioinspired liquid-based encapsulation strategy that offers protection from water without sacrificing the operational properties of the encapsulated materials. Using halide perovskite as a model system, we show that damage to the perovskite from exposure to water is drastically reduced when it is coated by a polymer matrix with infused hydrophobic oil. With a combination of experimental and simulation studies, we elucidated the fundamental transport mechanisms of ultralow water transmission rate that stem from the ability of the infused liquid to fill-in and reduce defects in the coating layer, thus eliminating the low-energy diffusion pathways, and to cause water molecules to diffuse as clusters, which act together as an excellent water permeation barrier. Importantly, the presence of the liquid, as the central component in this encapsulation method provides a unique possibility of reversing the water transport direction; therefore, the lifetime of enclosed water-sensitive materials could be significantly extended via replenishing the hydrophobic oils regularly. We show that the liquid encapsulation platform presented here has high potential in providing not only water protection of the functional device but also flexibility, optical transparency, and self-healing of the coating layer, which are critical for a variety of applications, such as in perovskite solar cells and bioelectronics. 

Abstract Photo‐electrochemistry is the major trajectory for directly transforming solar energy into chemical compounds. The performance of a photo‐electrochemical (PEC) system is directly related to the interfacial electrical band energy landscape. Recently, piezotronics has stood out as a promising strategy for tuning interfacial energetics. It applies intrinsic or deformation‐induced ionic displacements (ferroelectric and piezoelectric polarizations) to engineer the interfacial charge distribution, and thereby the band structures of PEC electrodes. Here, contemporary research efforts of coupling piezotronics with photo‐electrochemisty are reviewed. Quantitative band diagrams of a polarization‐tuned semiconductor–electrolyte junction are first introduced, with an emphasis on the impact of interface chemistry. Experimental advances of employing piezoelectric and ferroelectric polarizations to enhance the charge separation and transportation, and surface kinetics of PEC water splitting are discussed. Finally, critical challenges of applying piezotronics in PEC systems and promising solutions are presented.