Passivating contacts for high-efficiency silicon-based solar cells: from single-junction to tandem architecture

Abstract The electricity market from renewable energies is strongly driven by the pursuit of high energy conversion efficiency, which at present represents the most effective pathway to achieve substantial cost reductions. Silicon (Si) have been dominating the photovoltaic industry for decades, while the conversion efficiencies of Si single-junction solar cells are practically limited to around 27 %, and intrinsically constrained to 29.4 %. To tackle this long-term bottleneck, it is necessary to develop novel technologies and transfer them into industrial production. This paper commences with a review concentrating on two critical concepts enabling high-efficiency Si-based solar cells: passivating contacts and tandem technologies. Since the gradual evolution from full area Al back surface field cells to passivated emitter and rear contact cells, passivating contacts are considered as an essential concept to circumvent the recombination losses caused by the contacts. The theoretical background of the three prominent technologies for passivating contacts and their application prospects to solar cells are described in detail. The fundamental limit of single junction Si solar cells is attainable with the introduction of passivating contacts. To obtain conversion efficiencies greater than 30 %, upgrading Si with a high-bandgap tandem partner is a promising approach to improve the utilization of the solar spectrum, having the potential to produce efficiency surpassing the single junction Shockley–Queisser limit. Si is proven to be an ideal bottom cells material in tandem architectures due to its appropriate bandgap for the lower sub-cell and the advantage of compatibility with existing production lines, the technologies for crystalline Si as bottom-cell are already quite mature with a gigawatt scale. The two widely considered ideal options for the top-cell, i.e., III/V and perovskites, are summarized, respectively. Building on these two concepts, a clear technology route is provided to maximize energy conversion efficiency by integration of passivating contacts into Si based tandem solar cells. According to this discussion, guidelines for further developments of Si photovoltaics emerge clearly, proving that Si will continue to maintain its irreplaceable position in photovoltaics in the long term.