Carrier population control and surface passivation in solar cells

• Published in: Solar energy materials and solar cells 2018-09, Vol.184, p.38-47
• Main Authors: Cuevas, Andres, Wan, Yimao, Yan, Di, Samundsett, Christian, Allen, Thomas, Zhang, Xinyu, Cui, Jie, Bullock, James
• Format: Article
• Language: English
• Subjects: Carrier density; Carrier-selective contacts; Conductivity; Current carriers; Electrons; Organic chemistry; Passivity; Photovoltaic cells; Population control; Recombination; Silicon; Silicon solar cells; Solar cells; Surface charge; Surface passivation
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2018.04.026

Controlling the concentration of charge carriers near the surface is essential for solar cells. It permits to form regions with selective conductivity for either electrons or holes and it also helps to reduce the rate at which they recombine. Chemical passivation of the surfaces is equally important, and it can be combined with population control to implement carrier-selective, passivating contacts for solar cells. This paper discusses different approaches to suppress surface recombination and to manipulate the concentration of carriers by means of doping, work function and charge. It also describes some of the many surface-passivating contacts that are being developed for silicon solar cells, restricted to experiments performed by the authors. •The principles for passivating the surfaces of crystalline silicon and developing carrier-selective contact systems are described.•The metal oxides Ga2O3, TiO2,Ta2O5, HfO2 and ZrO2 are shown to passivate silicon surfaces.•High work function materials, like MoOx, or low work function ones, like Ca, Mg, LiFx, MgFx and MgOx, selectively extract holes orelectrons.•Solar cells with such selective contacts in a partial or full-area configuration have conversion efficiencies above 20%.•Two polysilicon/SiO2 passivating contact technologies are demonstrated with 24.7% (n-type) and 23.0% (p-type) efficient solar cells.