Probing the Mg2Si/Si(111) heterojunction for photovoltaic applications

[Display omitted] •Low-temperature MBE growth of Mg2Si film on Si(111) substrate.•Minority-carrier lifetime up to 7.3 µs is measured for Mg2Si film.•Photoresponse range is (380–1400)nm under zero bias at room temperature.•First demonstration of Mg2Si/Si heterojunction solar cell with 0.24% efficiency.•Carrier lifetime and energy conversion are limited by Mg2Si non-epitaxial grains. n-Mg2Si/p-Si heterojunction solar cell with a 1.4 µm thick unintentionally doped (n = 3 × 1017cm−3) silicide epitaxial layer on p-Si(111) (p = 5 × 1014cm−3) was grown by low temperature (250 °C) molecular beam epitaxy. Heterojunction demonstrated clear rectification and zero bias photoresponse in the (400–1400)nm wavelength range at room temperature. Under AM 1.5 illumination, an open-circuit voltage of 0.21 V, a short-circuit current density of 3.3 mA/cm2, fill factor of 0.36 were obtained while the conversion efficiency reached 0.24%, which is the pioneering demonstration of Mg2Si-based solar cell operation. Combined minority-carrier lifetime, Raman and AFM mapping together with TEM and XRD data revealed that carrier dynamics and photovoltaic performance are limited by the presence of non-epitaxial Mg2Si grains in the upper silicide film layer. However, minority-carrier lifetime up to 7.3 µs for Mg2Si demonstrates its great potential as absorbing material for Si-based solar cells.