A thin-film solar cell of high-quality ββ-FeSi2/Si heterojunction prepared by sputtering

High-quality (1 1 0)/(1 0 1)-oriented epitaxial ββ-FeSi2 films were fabricated on Si (1 1 1) substrate by the sputtering method. The critical feature was the formation of a high-quality thin ββ-FeSi2 template buffer layer on Si (1 1 1) substrate at low temperature. It was demonstrated that the template is very important for the epitaxial growth of thick ββ-FeSi2 films and for the blocking of Fe diffusion into the Si at the ββ-FeSi2/Si interface. Hall effect measurements for ββ-FeSi2 films showed n-type conductivity, with residual electron concentration around 2.0 × 1017 cm−3 and mobility of 50–400 cm2/V s. A prototype thin-film solar cell was fabricated by depositing n-ββ-FeSi2 on p-Si (1 1 1). Under 100 mW/cm2 sunlight, an energy conversion efficiency of 3.7%, with an open-circuit voltage of 0.45 V, a short-circuit current density of 14.8 mA/cm2 and a fill factor of 0.55, was obtained.