SnS2@SnO2 heterojunctions encapsulated in N-doped hollow mesoporous carbon spheres as high-efficiency counter electrodes for DSSCs

To address the high cost and scarcity of traditional platinum (Pt) counter electrodes, this study designed a novel non-Pt counter electrode material: nitrogen-doped hollow mesoporous carbon sphere (NCS)-loaded SnS 2 @SnO 2 heterojunctions (SnS 2 @SnO 2 /NCSs). By optimizing the mass ratio of Sn/S precursors to NCSs, the morphology of the composite was tailored. Comprehensive characterization via XRD, XPS, SEM, TEM, and Raman spectroscopy revealed that SnS 2 @SnO 2 nanoparticles (10–20 nm) were uniformly distributed within the internal/external walls and cavities of the NCSs via mesoporous confinement, forming a 3D conductive network. Nitrogen doping (I D /I G  = 1.12) endowed the carbon matrix with abundant active sites, while the band alignment of the SnS 2 @SnO 2 heterojunction significantly enhanced catalytic activity. Electrochemical tests demonstrated a charge transfer resistance (R ct  = 22.25 Ω·cm 2 ) close to Pt (15.78 Ω·cm 2 ), with reduced low-frequency diffusion impedance. When integrated into dye-sensitized solar cells (DSSCs), the SnS 2 @SnO 2 /NCSs-based device achieved a power conversion efficiency (PCE) of 7.32% (J sc  = 17.23 mA·cm⁻ 2 , V oc  = 737.46 mV, FF = 0.57), representing a 36% improvement over the pure heterojunction (5.38%) and approaching Pt-based devices (8.39%). This work provides a cost-effective strategy for developing high-performance non-Pt counter electrodes.