Thin film a-Si/c-Si1−xGex/c-Si heterojunction solar cells with Ge content up to 56%

Thin film a-Si(n⁺)/c-Si_1-xGe_x(p)/c-Si(p⁺) heterojunction solar cells are fabricated with Ge content up to 56 atomic percent. Solar cells with junction layers consisting of Si, Si_0.75Ge_0.25, Si_0.59Ge_0.41, and Si_0.44Ge_0.56 are compared to study the effect of increasing Ge concentration. The measured short-circuit current (J_sc) increases from ~14 mA/cm² for Si cells to 21 mA/cm² for the Si_0.44Ge_0.56 cells, for one light pass and a 2 μm-thick SiGe layer. The results show an open-circuit voltage (V_oc) of 0.61 V for Si cells, dropping to 0.32 V for Si_0.44Ge_0.56, consistent with the reduction in band-gap. Quantum efficiency measurements highlight the improved spectral response for higher Ge percentages. Physics based TCAD simulations combined with the experimental results are used to extract lifetime and interface velocity.