Editorial: Passivating contact solar cells

In the last decade, significant attention has been given to the concept of passivating contact solar cells. Such cells are characterised by very low contact recombination and low contact resistance, a combination that is challenging to achieve with conventional diffused silicon layers. These cells demonstrate a very high open-circuit voltage and therefore higher efficiency. Passivating contacts can be classified into three main technologies according to the material used for the charge-carrier selection: (i) doped amorphous silicon; (ii) doped polycrystalline silicon; and (iii) metal compounds and organic materials. Due to the impressive progress of passivating contacts and the wide variety of technologies and approaches, Progress in Photovoltaic decided to dedicate an entire issue to reviewing the status of this concept. The issue starts with a review of the three main technologies of passivating contacts, summarising their current efficiencies and discussing their distinctive features, advantages, and limitations. While doped amorphous silicon has been used for the manufacturing of industrial heterojunction solar cells for decades, polycrystalline silicon-based solar cells have only recently entered mass production. Interestingly, this technology was introduced to bipolar transistors as early as the 1970s and adapted into silicon solar cells in the 1980s. However, because some aspects other than the contacts limited the obtainable solar cell efficiencies, this technology was not actively investigated until 2013. Nevertheless, since then, a substantial amount of research has been done by several research institutes and companies, enhancing the performance of polycrystalline silicon-based solar cells to efficiencies above 26%. More importantly, significant effort has been made to commercialise this technology with significant progress already reported by several photovoltaic companies. As doped polycrystalline silicon seems to be the most mature passivating contact technology, we review the status of the three leading approaches: The POLO of ISFH, the TOPCon of Fraunhofer ISE, and the monoPoly of SERIS. With several large manufacturers announcing their plans to transfer polycrystalline silicon-based technology into mass production, we also review the activities that have been taken to push the boundaries of this technology and enabled its integration into existing production lines. Manufacturing options, as well as necessary technological advances in cell metallisation and module integration, are discussed from the industrial perspective. We then review the progress of passivating contact technologies that employ metal compounds as the carrier-selective layer. The interest in this technology has recently increased with a few promising families of materials having demonstrated excellent results, specifically alkali/alkaline-earth metal compounds and transition-metal oxides. The number of successful demonstrations of selective-contact materials within these families is increasing fast, with the best solar cell efficiencies now exceeding 23%. The challenges of this technology to be considered for industrial adoption are then discussed, together with its prospects in the context of silicon photovoltaics. In a separate paper, we provide a detailed techno-economic analysis of the use of atomic layer deposited transition-metal oxides for the fabrication of silicon solar cells. The special issue concludes with a paper discussing the challenges and opportunities in the metallisation of industrial perovskite/silicon tandem solar cells. We want to thank all the authors for their great contributions. It was a pleasure to work with such a talented and diverse group of researchers. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.