Tuning the band gap and polarization of BaSnO3/SrSnO3 superlattices for photovoltaic applications

Band gap and polarization are two important quantities for enhancing the performance of photovoltaic materials. Based on first-principles calculations, we demonstrate that direct band gap and hybrid improper ferroelectric polarization coexist in BaSnO3/SrSnO3 superlattices. Furthermore, the band gap and polarization can be simultaneously tuned by mechanical strain and pressure. In the presence of tensile strain or negative pressure, the band gap is substantially lowered and the polarization is enhanced by about five times in comparison with that without mechanical loads. The lowered band gap is necessary for increasing the efficiency of light absorption, whereas the enhanced polarization is desirable for the separation of photo-excited carriers in the materials. The present work suggests that the strained BaSnO3/SrSnO3 superlattices are promising ferroelectric semiconducting materials for photovoltaic applications.