Large-Area Thin-Film Free-Standing Monocrystalline Si Solar Cells by Layer Transfer

This paper describes our progress achieved in thin-film free-standing monocrystalline silicon (FMS) solar cells by layer transfer process using porous silicon. The highest cell efficiency achieved for a 1times1 cm² FMS solar cell is 13.5% with an open circuit voltage V_oc=612 mV, current density J_sc =28.9 mA/cm² and fill factor of FF=76.7%. In the effort of scaling-up of the cell area, the lift-off process was adapted to 10times10 cm² substrates. The large-area epilayers from APCVD and LPCVD, respectively, were successfully processed into FMS solar cells, giving the best efficiency of 11.4% for the APCVD-FMS cell with an area of 11.1 cm². Detailed study by quantum efficiency measurements, combined with SEM, revealed that the enhanced internal quantum efficiency and reflectance in the spectral range of lambda>825 nm for the APCVD-FMS cell can be attributed to the internal light reflection from the well-defined interface between the epilayer and the sintered porous, or quasi-monocrystalline silicon (QMS) layer