Abstract
Several techniques have been proposed for kerfless wafering of thin Si wafers, which is one of the most essential techniques for reducing Si material loss in conventional wafering methods to lower cell cost. Proton induced exfoliation is one of promising kerfless techniques due to the simplicity of the process of implantation and cleaving. However, for application to high efficiency solar cells, it is necessary to cope with some problems such as implantation damage removal and texturing of (111) oriented wafers. This study analyzes the end-of-range defects at both kerfless and donor wafers and ion cutting sites. Thermal treatment and isotropic etching processes allow nearly complete removal of implantation damages in the cleaved-thin wafers. Combining laser interference lithography and a reactive ion etch process, a facile nanoscale texturing process for the kerfless thin wafers of a (111) crystal orientation has been developed. We demonstrate that the introduction of nanohole array textures with an optimal design and complete damage removal lead to an improved efficiency of 15.2% based on the kerfless wafer of a 48 μm thickness using the standard architecture of the Al back surface field.
Highlights
Si wafers for crystalline Si solar cells, produced by multi-wire sawing the Si ingot grown by a Czochralski method, have been consistently thinner to lower cell cost by reducing material consumption[1,2,3]
The stress-induced technique or SLIM-cut employs a stress induced layer on the Si wafer, and the stress is activated by thermal expansion mismatch between the stress layer and the Si wafer for spalling of thin wafers[13]
A critical proton dose for exfoliation of thin wafers relies on the crystal orientation of the parent Si wafers
Summary
Hyeon-Seung Lee[1,2], Jaekwon Suk[3], Hyeyeon Kim[3], Joonkon Kim[3], Jonghan Song[3], Doo Seok Jeong 1, Jong-Keuk Park[1], Won Mok Kim[1], Doh-Kwon Lee[4], Kyoung Jin Choi[5], Byeong-Kwon Ju2, Taek Sung Lee1 & Inho Kim[1]. In the EAS process, a thin stress layer is electro-deposited at room temperature, and the lattice mismatch between the stress layer and the wafer induces a large stress field, which causes the lift-off of a thin Si wafer without high temperature annealing Another kerfless wafering technique based on a smart cut technique invented in 1990’s was attempted to fabricate kerfless wafers of tens of micrometer thickness for Si solar cells using a MeV proton implanter[15,16]. The proton induced exfoliation technique is a relatively simple and clean vacuum process compared with the epitaxial Si lift-off method[20] In this technique, a critical proton dose for exfoliation of thin wafers relies on the crystal orientation of the parent Si wafers. We analyze an EOR defect zone thickness induced by proton implantation and develop a texturing process for the kerfless-thin wafers of a (111) crystal orientation. We discuss the effect of rear side modifications for effective light trapping in thin kerfless wafers
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
