Theoretical analysis of built-in interfacial electric dipole field in dye-sensitized solar cells

The built-in electric field formed between the involved species at the heterogeneous interface can affect the overall performance of dye-sensitized solar cells (DSSCs). The direct experimental observation on the built-in electric field is challenging due to the intricate heterogeneous interface itself. Herein, we propose a novel strategy for exploring the nature of the built-in electric field in the functionality of DSSCs by using externally applied electric field as perturbation to couple to the built-in electric field. As a matter of fact, the built-in electric field refers to the interfacial electric field (F_dipole) induced by the charge separation occurring at heterogeneous dye/semiconductor interface. On the basis of theoretical calculations, we found that F_dipole couples to external electric field through the electric dipole moment change (Δμ_ET) at dye/semiconductor heterointerface to affect the photoelectronic properties in DSSCs. In essence, the influence of gap states and conduction bands is determined by the overlap between the applied electric field and intrinsic dipole moment change of charge-separated dye/semiconductor. Furthermore, the electron-transfer rate (k_ET) is also intrinsically related to the coupling of F_dipole with external electric field in the form of electric dipole moment at dye/semiconductor interface. In addition, applying external electric field is demonstrated to be an approach to modulate the interfacial electric dipole moment field to achieve better performance of DSSCs. Our theoretical finding can provide insight into designed strategies for understanding the functionality of DSSCs and offer a universal route to study the heterogeneous interfaces in DSSCs experimentally and theoretically.