Study of the Piezoelectric Properties of UV-Selective Optically Transparent Zn(O,S) Based Solar Cells

Abstract

Hybrid photovoltaic and piezoelectric structures can convert photons to electrical energy by using the photovoltaic part and mechanical energy to electrical energy by using the piezoelectric part, in the presence of rain, wind etc, where there is not enough sunlight for photo-conversion. To date, state-of-the art UV-selective solar cells are mainly based on the use of zinc oxide (ZnO) as the absorber material. ZnO presents high absorption coefficient (α(λ) > 104 cm−1 for λ < 390 nm) and a direct energy bandgap of 3.37 e V. By anion alloying ZnO with sulfur (S), it is possible to fabricate Zn(O,S) mixed crystals that present a bandgap energy bowing with a reported minimum value at 2.7 eV, presenting a more optimal spectral match with the UV region. These structures can be used to create UV-selective solar cells with high transparency in the visible region, that can be utilized in many applications including the development of nonintrusive building-integrated photo-voltaic (BIPV) elements as transparent solar windows and glass-based solar façades. In addition, ZnO and Zinc Sulfide (ZnS) have the ability to convert applied mechanical strain energy to harvestable electrical energy in nano/microdevice. The wurtzite ZnO and ZnS materials exhibit excellent piezoelectric property along the [0001] direction because of their non-centrosymmetric structure. Therefore, in this research we conducted molecular dynamic (MD) simulations on a selected UV-TPV Zn(O1–xSx) structures and reported their polarization and the piezoelectric constants and compared them to pure ZnO and ZnS structures. The MD results show that the polarization and piezoelectric constants values were all intermediate between those obtained for ZnO and ZnS bulk structures, indicating good piezoelectric properties for the Zn(O1–xSx) structures.