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Huge energy consumption and running out of fossil fuels has led to the advancement of renewable sources of power, including solar, wind, and tide. Among them, solar cells have been well developed with the significant achievement of silicon solar panels, which are popularly used as windows, rooftops, public lights, etc. In order to advance the application of solar cells, a flexible type is highly required, such as layered casting solar cells (LCSCs). Organic solar cells (OSCs), perovskite solar cells (PSCs), or dye-sensitive solar cells (DSSCs) are promising LCSCs for broadening the application of solar energy to many types of surfaces. LCSCs would be cost-effective, enable large-scale production, are highly efficient, and stable. Each layer of an LCSC is important for building the complete structure of a solar cell. Within the cell structure (active material, charge carrier transport layer, electrodes), hole transport layers (HTLs) play an important role in transporting holes to the anode. Recently, diverse HTLs from inorganic, organic, and organometallic materials have emerged to have a great impact on the stability, lifetime, and performance of OSC, PSC, or DSSC devices. This review summarizes the recent advances in the development of inorganic, organic, and organometallic HTLs for solar cells. Perspectives and challenges for HTL development and improvement are also highlighted.

Chitosan is a natural polymer that has been widely utilized for many purposes in the food, textile, agriculture, water treatment, cosmetic and pharmaceutical industries. Based on its characteristics, including biodegradability, non-toxicity and antimicrobial properties, it has been employed effectively in wound healing applications. Importantly, however, it is necessary to improve chitosan's capacities by combination with zinc oxide (ZnO), titanium dioxide (TiO₂) and silver (Ag) nanoparticles (NPs). In this review of many of the latest research papers, we take a closer look at the antibacterial effectiveness of chitosan combined with ZnO, TiO₂ and Ag NPs and also evaluate the specific wound healing application potentials.