Both sides now: Optimal bifaciality with silicon heterojunction solar cells

Two-terminal tandem solar cells based on perovskite/silicon (PK/ Si) technology represent one of the most exciting pathways towards pushing solar cell efficiencies beyond the thermodynamic limit of single-junction crystalline silicon devices. While laboratory efficiencies of these tandem cells have risen to very impressive levels, many important innovations towards enabling their eventual manufacturability have also been made in this rapidly evolving field. In this paper, a number of these processing innovations are highlighted in order to give a more complete view as to the viability of scaling up the processing of these devices. Specifically, the focus is placed on how today’s crystalline silicon process flows could be adapted in order to allow existing cell lines to produce PK/Si cells.

This paper presents a way to evaluate production windows and related field issues using an adapted failure mode and effects analysis (FMEA) approach. Since PV modules are the most important component in terms of longevity and warranties, the focus of Fraunhofer’s work has been on module manufacturing. The process, however, can also be applied to cell manufacturing and other steps in the value chain.

Low-temperature interconnection processes for high-efficiency PV cells will be a key R&D topic in the coming years. In reality, to avoid significant deterioration of the surface passivation, the metallization and interconnection processes of silicon heterojunction (SHJ) cells are limited to temperatures below 200°C; tandem cells with a perovskite subcell demand an even greater reduction in process temperature, namely below 130°C. Moreover, to ensure the sustainability of PV production on a TW scale, the use of scarce materials, especially silver, needs to be reduced, as 10% of the world’s supply was already dedicated to PV in 2020. This paper addresses the results obtained in terms of reducing the silver consumption in interconnection technology based on electrical conductive adhesive (ECA) and Pb-free ribbons.

After several years of technological developments, measurement and quality standard specifications, and bifaciality implementations in energy yield simulation programs, bifacial PV has become reliable and will shortly become accepted as a valuable commodity. Since 2020, bifacial passivated emitter and rear cell (PERC) technology has been king of the energy markets, and, in combination with simple tracking systems (e.g. horizontal single-axis tracking – HSAT), the lowest electricity costs have been achieved. Because PERC is reaching its limit in terms of efficiency, and n-type technology is gaining momentum, in the future n-type PV (nPV) will replace PERC technology as the workhorse of the PV electricity market. This paper describes why, and most likely when, this will happen and which n-type technologies will be leading the pack in the race to bring electricity costs well below €0.01/kWh.

As the PV industry rapidly advances towards annual PV production and installations on a terawatt scale, many aspects that are currently not critical will need to be considered. Among these, material availability is probably one of the most pressing ones. Established production routines will need to be changed, which may pose significant time constraints in the light of the fast-growing market. The focus of this paper will be on the use of silver for solar cell metallization. Past developments are discussed and an overview is given of the fast-growing number of relevant publications from the scientific community that deal with the problems associated with silver.

This paper reviews the steps to making a breakthrough in TOPCon efficiency, from cell to PV module, by using industrially viable manufacturing processes. A detailed characterization and investigation of the primary losses of JinkoSolar’s TOPCon record cell of July 2020, with an efficiency of 24.8%, is presented.