Selenium is an essential trace element important for many physiological processes, especially for the functions of immune and reproductive systems, metabolism of thyroid hormones, as well as antioxidant defense. Selenium deficiency is usually manifested by an increased incidence of retention of placenta, metritis, mastitis, aborts, lowering fertility and increased susceptibility to infections. In calves, lambs and kids, the selenium deficiency demonstrates by WMD (white muscle disease), in foals and donkey foals, it is associated with incidence of WMD and yellow fat disease, and in pigs it causes VESD (vitamin E/selenium deficiency) syndrome. The prevention of these health disorders can be achieved by an adequate selenium supplementation to the diet. The review summarizes the survey of knowledge on selenium, its biological significance in the organism, the impact of its deficiency in mammalian livestock (comparison of ruminants vs. non-ruminants, herbivore vs. omnivore) and possibilities of its peroral administration. The databases employed were as follows: Web of Science, PubMed, MEDLINE and Google Scholar.

Solar energy is free from noise and environmental pollution. It could be used to replace non-renewable sources such as fossil fuels, which are in limited supply and have negative environmental impacts. The first generation of solar cells was made from crystalline silicon. They were relatively efficient, however very expensive because they require a lot of energy to purify the silicon. Nowadays, the production of solar cells has been improved since the first generation (thin-film solar cells, dye-sensitized solar cells, perovskite solar cells, and organic solar cells). In this work, the development of solar cells was discussed. The advantages, limitations, challenges, and future trends of these solar cells were also reported. Lastly, this article emphasized the various practices to promote solar energy and highlighted the power conversion efficiency of the fabricated devices.

Zinc oxide (ZnO) has been widely studied over the last decade for its remarkable properties in optoelectronic and photovoltaic devices because of its high electron mobility and excitonic properties. It has probably the broadest range of nanostructured forms that are also easy and cheap to synthesize using a wide variety of methods. The volume of recent work on ZnO nanostructures and their devices can potentially overshadow significant developments in the field. Therefore, there is a need for a concise description of the most recent advances in the field. In this review, we focus on the effect of ZnO nanostructure morphologies on the performance of ZnO-based solar cells sensitized using methylammonium lead iodide perovskite. We present an exhaustive discussion of the synthesis routes for different morphologies of the ZnO nanostructure, ways of controlling the morphology, and the impact of morphology on the photoconversion efficiency of a given perovskite solar cell (PSC). We find that although the ZnO nanostructures are empirically similar, one-dimensional structures appear to offer the most promise to increasing photoconversion efficiency (PCE) by their proclivity to align and form vertically stacked layers. This is thought to favor electron hopping, charge mobility, and conductivity by allowing multiple charge conduction pathways and increasing the effective junction cross-sectional area. The combined effect is a net increase in PCE due to the reduced surface reflection, and improved light absorption.

This review provides detailed information on perovskite solar cell device background and monitors stepwise scientific efforts applied to improve device performance with time. The work reviews previous studies and the latest developments in the perovskite crystal structure, electronic structure, device architecture, fabrication methods, and challenges. Advantages, such as easy bandgap tunability, low charge recombination rates, and low fabrication cost, are among the topics discussed. Some of the most important elements highlighted in this review are concerns regarding commercialization and prototyping. Perovskite solar cells are generally still lab-based devices suffering from drawbacks such as device intrinsic and extrinsic instabilities and rising environmental concerns due to the use of the toxic inorganic lead (Pb) element in the perovskite (ABX₃) light-active material. Some interesting recommendations and possible future perspectives are well articulated.

Perovskite solar cells (PSCs) hold great promise for cost‐effective and high‐efficiency solar energy conversion. However, in practice, they face practical limitations due to suboptimal electron transport, inadequate hole‐suppression, photocatalytic instability, and susceptibility to other environmental factors. Many transition metal oxides such as ZnO and TiO₂ have important excitonic properties that make them good electron transport layer (ETL) materials in PSCs. However, many of the PS limitations arise from inherent issues with these oxides. The high interest in TiO₂ is due to its low toxicity, chemical stability, and the potential to enhance its excitonic performance through doping with many materials. The main limitations of TiO₂ are its poor visible‐light response by virtue of its wide bandgap of ~3.2 eV, and its high electron‐hole (e‐h) recombination rates, which are directly responsible for its low current densities. Transition metal oxide enhancements occur using either internal doping or surface sensitization. Of the added materials, graphene has exceptional electrical conductivity, high electron mobility, large surface area, and excellent mechanical properties, making it a near‐ideal candidate to improve the performance of TiO₂. This review examines the important advances in graphene‐TiO₂ (g‐TiO₂) composites for ETL application. By forming a composite with TiO₂, graphene can significantly enhance electron transport, reduce recombination losses, and improve the overall stability of PSCs. We present the detailed rationale for and analysis of g‐TiO₂ for improved electron transport efficiency, enhanced stability, and boosted overall PSC performance with the objective of providing an authoritative resource for the field.