3D hierarchical FeSe₂ microspheres: Controlled synthesis and applications in dye-sensitized solar cells

Mastery over the structures at nano/microscale can effectively tailor the catalytic activity and durability of materials. Herein, three dimension (3D) hierarchical iron diselenide (FeSe₂) microspheres have been successfully synthesized via a hot-injection method. The morphologies of building blocks and final products can be simply controlled by the amount and/or the type of alkythiols, from irregular micro/nanoparticles to uniform 3D hierarchical microspheres made of ultrathin nanosheets or rhombus-like nanorods. A formation mechanism has been understood based on the inherent crystal structure of FeSe₂ and the selective adsorption of alkythiols. The as-obtained FeSe₂ samples were employed as counter electrode (CE) materials in dye-sensitized solar cells (DSSCs). Electrochemical characterizations indicated that the 3D hierarchical FeSe₂ microspheres composed of ultrathin nanosheets (FeSe₂ NSs) exhibited low charge transfer resistance at the electrolyte-electrode interface, high electrocatalytic activity and fast reaction kinetics for the I^-/I₃^- redox reaction. A DSSC with FeSe₂ NSs CE achieved a high power conversion efficiency of 8.39% under a simulated solar illumination of 100mWcm^-2 (AM 1.5), comparable to that of Pt based devices (8.20%). Moreover, the fast activity onset and relatively long stability demonstrated that the FeSe₂ NSs is a promising alternative to Pt in DSSC.