Optical and electrical performance of rear side epitaxial emitters for bifacial silicon solar cell application

• Published in: Solar energy materials and solar cells 2019-06, Vol.195, p.43-48
• Main Authors: Li, Yuandong, Recamán Payo, Maria, Singh, Sukhvinder, Chen, Jia, Duerinckx, Filip, Hajjiah, Ali, Poortmans, Jef
• Format: Article
• Language: English
• Subjects: Cytology; Electromagnetic absorption; Emitter; Emitters; Epitaxial growth; Epitaxial layers; Epitaxy; Light trapping; Metallizing; Morphology; PERT; Photovoltaic cells; Pyramids; Recombination; Rounding; Silicon solar cell; Solar cells; Substrates
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2019.01.051

In this work we investigated the optical and electrical performance of p-type epitaxial layers as the rear emitter of bifacial n-type PERT solar cells. In the first part of this paper, the surface morphology of epitaxial layers grown on textured surfaces is studied. Because of the epitaxial growth, a pyramids-rounding effect is observed as a result of {311} and {911} facet propagation. The growth pattern was quantified and modelled. In the second part of this paper, the optical performance of semi-device test structures is evaluated. The trend of the optical results in bifacial solar cell structures indicates that a final pyramid angle at the rear side around 20° gives the maximum light absorption in the wafer substrate. In this work we demonstrate that the epitaxial growth of the emitter on the textured rear side of these devices can already give a pyramid angle of 25° without having to introduce any additional polishing steps to modify the morphology of the textured surface. In the last part of this paper, we present the electrical results for semi-device structures created to quantify the recombination losses in the passivated and metallized regions of those p-type epitaxial emitters. These results indicate that by introducing a rear epitaxial emitter in the bifacial n-type PERT cell structure, we can increase the implied Voc up to 17 mV compared to a diffused emitter with the same sheet resistance. •The pyramids-rounding effect is simultaneously implemented during the epitaxial emitter growth step.•The trend of the optical results in bifacial solar cell structures indicates that a final pyramid angle at the rear side around 20° gives the maximum light absorption in the wafer substrate. In this work we demonstrate that the epitaxial growth of the emitter on the textured rear side of these devices can already give a pyramid angle of 25 ° without having to introduce any additional polishing steps to modify the morphology of the textured surface.•Thick but lowly doped epitaxial emitters reduce recombination loss compared to diffused counterpart.