Self-assembled bulk nanostructured Bi2Se3/CdSe heterojunction synthesized by a single step spinodal decomposition of Bi2.4Cd0.8Se4.4

Spinodal and binodal decomposition were used here to drive the formation of self-assembled bulk Bi2Se3/CdSe (i.e. topological insulator / trivial semiconductor) heterojunctions. As a first step, we determined the formation conditions of the stable layered compound, whose stoichiometry was quantified to be Bi2.4Cd0.8Se4.4, and we investigated its crystalline, surface chemical and electronic properties. After this, a systematic study allowed us to establish the thermodynamic and kinetic conditions necessary to achieve phase separation of Bi2.4Cd0.8Se4.4 in the spinodal and binodal regimes. In the spinodal bulk heterojunction material the widths of the CdSe and Bi2Se3 lamellar structures were ~25 to 100 nm and ~80 to 130 nm, respectively. In the binodal bulk heterojunction material, we observed drop-like CdSe crystallites ranging in size from ~ 20 nm to 1 m within the Bi2Se3 matrix. Moreover, the junction between Bi2Se3 and CdSe, was found to be atomically abrupt for both spinodal and binodal patterns. This approach offers a facile self-driven one-step alternative procedure to the complex and expensive multi-step artificial growth methods typically used to produce nanostructured all-inorganic bulk heterojunction materials for future applications in the field of solar energy.