This tutorial review provides a fundamental understanding of different mechanisms, material selection, device optimization and applications of hydrovoltaic technology and provides a systematic collection of recent advances.

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Covalent organic frameworks (COFs) as a new class of crystalline, porous materials have attracted extensive attention in the fields of photocatalytic and photovoltaic applications. Generally, donor-acceptor (DA) structures play an important role in the charge separation efficiency of solar cells. In this study, two DA-COFs with high crystallinity, good porosity, and excellent stability are incorporated into the FAPbI 3 layer of perovskite solar cells. This addition of DA-COFs reduces the defect concentration and shallows the defect state. The donor-acceptor system in COFs also possesses strong charge-transfer pathway, which strongly prevents charge recombination to afford more efficient charge separation efficiency. The highest power-conversion efficiency of perovskite solar cells constructed with DA-COFs is 23.19% with excellent humidity stability of the solar cells. Therefore, this work provides a pathway for using DA-COFs to fabricate perovskite solar cells with higher efficiency and stability.

Water-evaporation-induced (WEI) electricity generation has been widely studied, but the explanation for the working mechanism remains controversial yet. In this study, porous carbon black (CB) films with multiple parallel electrodes were prepared and the voltage distribution in these films was investigated during WEI electricity generation. We found that in both toluene and ethanol CB films, voltage between neighboring electrodes increases first but then decreases with increasing height above the bulk water surface. This voltage distribution derives from similar volumetric flow rate distribution of water inside the film, which is caused by the hydrophilicity of film and water evaporation. Our results support streaming potential and present more details during WEI electricity generation. It is helpful for understanding the mechanism in other material systems as well.

Atmospheric water is ubiquitous on earth and extensively participates in the natural water cycle through evaporation and condensation. This process involves tremendous energy exchange with the environment, but very little of the energy has so far been harnessed. The recently emerged hydrovoltaic technology, especially moisture‐induced electricity, shows great potential in harvesting energy from atmospheric water and gives birth to moisture energy harvesting devices. The device performance, especially the long‐term operational capacity, has been significantly enhanced over the past few years. Further development; however, requires in‐depth understanding of mechanisms, innovative materials, and ingenious system designs. In this review, beginning with describing the basic properties of water, the key aspects of the water–hygroscopic material interactions and mechanisms of power generation are discussed. The current material systems and advances in promising material development are then summarized. Aiming at the chief bottlenecks of limited operational time, advanced system designs that are helpful to improve device performance are listed. Especially, the synergistic effect of moisture adsorption and water evaporation on material and system levels to accomplish sustained electricity generation is discussed. Last, the remaining challenges are analyzed and future directions for developing this promising technology are suggested.