Ferroelectric polarization induced charge separation in BaTiO3/Si: A pathway for non-PN junction photovoltaics

Abstract

Solar energy is one of the most economical sources of renewable energy. The conventional solar cells are generally configured as PN or Schottky junctions where the absorbed sunlight is used to generate mobile electron-hole pairs and a built-in electric field separates the charge carriers. Further advances in solar photovoltaics are urgently desired to increase the performance at affordable cost. Herein, we introduce a new kind of solar cell concept which utilizes the surface bound charges of a ferroelectric (BaTiO3) for separating the charge carriers in silicon (Si). Based on the new type of charge separation mechanism, a high open circuit voltage (Voc) can be established in this type of cell configuration. The results have shown that after forward polarization, the photovoltaic effect can be achieved in the cell with both Al and Ti- electrodes. The photovoltaic properties on polarized cells of Al–Ti and Au–Ti electrodes were significantly improved where the polarization induced voltage (VP) increased greatly to be 52% of the Voc after poling. Furthermore, the results also indicated that the asymmetric ferroelectric polarization makes the major contribution to the photovoltaic effect. Theoretical simulations were also conducted for the cells, which confirmed that the electric field induced by the polarization of BaTiO3 also extended into the Si layer, resulting in the charge separation in Si. This study provides a new paradigm to design ferroelectric/semiconductor heterostructures for non-PN junction photovoltaic devices and solar energy harvesting.