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Human urine is universal unused waste material that is regularly disposed of by the human body. We, for the first time, presented an economically beneficial, sustainable, and novel route to synthesize mesoporous human urine carbon (HUC)-containing heteroatoms, i.e., C, Na, Cl, N, S, and P, using a human urine waste. The as-synthesized HUC were envisaged for their structural elucidation, morphology evolution, crystal structure, functional bonding, and elemental composition analyses through various sophisticated technologies. The HUC catalyst had a moderately crystalline nature due to the graphitic phase of carbon with a particle size of 20–50 nm, which was successfully used to synthesizing chromenes, 1,8-di-oxo-octahydroxanthenes, and benzypyrazolylcoumarin and biscoumarin derivatives through a one-pot multicomponent reaction with 20 mg of catalyst in EtOH/H2O solvent. This eco-friendly and simple method offers numerous advantages such as easy purification, clean reaction, and excellent yield for organic synthesis. The HUC catalyst can be recycled ten times and reused multiple times after activation without affecting catalytic performance.

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Perovskite solar cells (PSCs) are advancing rapidly and have reached a performance comparable to that of silicon solar cells. Recently, they have been expanding into a variety of applications based on the excellent photoelectric properties of perovskite. Semi-transparent PSCs (ST-PSCs) are one promising application that utilizes the tunable transmittance of perovskite photoactive layers, which can be used in tandem solar cells (TSC) and building-integrated photovoltaics (BIPV). However, the inverse relationship between light transmittance and efficiency is a challenge in the development of ST-PSCs. To overcome these challenges, numerous studies are underway, including those on band-gap tuning, high-performance charge transport layers and electrodes, and creating island-shaped microstructures. This review provides a general and concise summary of the innovative approaches in ST-PSCs, including advances in the perovskite photoactive layer, transparent electrodes, device structures and their applications in TSC and BIPV. Furthermore, the essential requirements and challenges to be addressed to realize ST-PSCs are discussed, and the prospects of ST-PSCs are presented.

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