CdTe is a very robust and chemically stable material and for this reason its related solar cell thin film photovoltaic technology is now the only thin film technology in the first 10 top producers in the world. CdTe has an optimum band gap for the Schockley-Queisser limit and could deliver very high efficiencies as single junction device of more than 32%, with an open circuit voltage of 1 V and a short circuit current density exceeding 30 mA/cm². CdTe solar cells were introduced at the beginning of the 70s and they have been studied and implemented particularly in the last 30 years. The strong improvement in efficiency in the last 5 years was obtained by a new redesign of the CdTe solar cell device reaching a single solar cell efficiency of 22.1% and a module efficiency of 19%. In this paper we describe the fabrication process following the history of the solar cell as it was developed in the early years up to the latest development and changes. Moreover the paper also presents future possible alternative absorbers and discusses the only apparently controversial environmental impacts of this fantastic technology.

Ambient energy harvesting has great potential to contribute to sustainable development and address growing environmental challenges. Converting waste energy from energy-intensive processes and systems (e.g. combustion engines and furnaces) is crucial to reducing their environmental impact and achieving net-zero emissions. Compact energy harvesters will also be key to powering the exponentially growing smart devices ecosystem that is part of the Internet of Things, thus enabling futuristic applications that can improve our quality of life (e.g. smart homes, smart cities, smart manufacturing, and smart healthcare). To achieve these goals, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and radiofrequency wireless power transfer. By bringing together the perspectives of experts in various types of energy harvesting materials, this Roadmap provides extensive insights into recent advances and present challenges in the field. Additionally, the Roadmap analyses the key performance metrics of these technologies in relation to their ultimate energy conversion limits. Building on these insights, the Roadmap outlines promising directions for future research to fully harness the potential of energy harvesting materials for green energy anytime, anywhere.

Thin film solar cells have reached commercial maturity and extraordinarily high efficiency that make them competitive even with the cheaper Chinese crystalline silicon modules. However, some issues (connected with presence of toxic and/or rare elements) are still limiting their market diffusion. For this reason new thin film materials, such as Cu₂ZnSnS₄ or SnS, have been introduced so that expensive In and Te, and toxic elements Se and Cd, are substituted, respectively, in CuInGaSe₂ and CdTe. To overcome the abundance limitation of Te and In, in recent times new thin film materials, such as Cu₂ZnSnS₄ or SnS, have been investigated. In this paper we analyze the limitations of SnS deposition in terms of reproducibility and reliability. SnS deposited by thermal evaporation is analyzed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and atomic force microscopy. The raw material is also analyzed and a different composition is observed according to the different number of evaporation (runs). The sulfur loss represents one of the major challenges of SnS solar cell technology.

Over the last 20 years, the technological improvements of CdTe solar cell have been impressive, and today the performance of these cells is comparable with that of silicon cells. Behind these important results, there have been important research efforts, aimed at exploring every single aspect related to CdTe cell optimization. One of these is reliability, that is fundamental in the perspective of massive commercialization. The aim of this review paper is to explore the main aspects related to the operation and reliability of CdTe solar cells, and describe the most relevant results presented in the literature on these topics. The paper is divided in two parts. The first is dedicated to a general introduction of CdTe issues. In this part, we report the most relevant details on CdTe solar cells from a reliability perspective, including (a) a description of the CdTe solar cells development on the years, (b) a description of the main production methods, (c) an overview of the main mathematical model to describe a solar cell, and (d) the main normative requirements related to solar cell reliability. The second section describes the most important papers in the field of CdTe solar cell reliability, along with two recent case studies, that can be used as an example to understand the complexity of the involved processes. The results are critically discussed by considering the most recent literature on the topic, to provide a general overview to the reader willing to approach the topic.