High-quality exfoliated crystalline silicon foils for solar cell applications

Abstract

Kerfless wafering techniques offer a significant cost saving potential via the reduction of silicon consumption. In this paper, we examine thin single crystalline Si foils that were fabricated by a novel kerfless thermo-mechanical exfoliation method utilizing evaporated Al with regard to their suitability for solar cell applications. The foils are 50-80 μm thick and smooth to visual inspection across the almost entire surface. We measure the effective minority carrier lifetimes of the foils and the remaining parent substrates by quasi-steady-state photoconductance (QSSPC) and spatially resolved by dynamically calibrated steady state infrared carrier lifetime mapping (dynILM). We find lifetimes of above 120 μs for kerfless exfoliated 0.5 Ωcm p-type float-zone (FZ) Si layers. With an additional etching step after exfoliation, we obtain effective lifetimes of above 200 μs. The measurements reveal that there is no critical lifetime degradation due to exfoliation-induced surface features and thus the exfoliated layers are well-suited for high-quality solar cells.