Exfoliation of Large-area Flexible Ultra-thin Silicon Films by Thermal Induced Pore Reorganization
Chih-Tse Chang1*, Chih-Chung Lai1, Yi-Chung Wang1, Yu-Lun Chueh1
1Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan
* presenting author:張志澤, email:handsam0723@hotmail.com
Fabrication of thin-film crystalline Silicon (Si) solar cells has several advantages compared to those fabricated by bulk silicon materials such as lower usage of material, extraordinary mechanical properties and comparable efficiency. However, the thinning process proposed including thinning the wafers, depositing thin films on low-cost substrates or using small cells in combination with concentrated optics are not actually cost effective. In this study, quasi-monocrystalline silicon films are fabricated by mechanically exfoliation of electrochemically anodized porous silicon (PS) after annealing at 1050 ℃ in pure hydrogen ambient for pore reorganization. The films thickness can be modulated and be repeatedly exfoliated from Si wafer under suitable etching and annealing conditions, where flexible Si films of 1.2 um thickness over 2.25 cm2 area are manufactured. The crystallinity of PS films were confirmed by grazing incident X-ray diffraction (GIXRD) while the field emission scanning electron microscopy (FE-SEM) revealed that the PS films had less defects, and its optical properties were verified to be improved after thermal treatment. The Hall measurements indicated that electrical property and carrier mobility of PS films were maintained after operated in high temperature environment. This approach regarding to ultra-thin flexible Si films opens up tremendous opportunities for future application in not only solar energy but also flexible devices technology.

Keywords: Porous Silicon, Pore Reorganization, Thin Film Exfoliation