Synergistic bandgap engineering of Nd2O3/Sr0.5Zn0.5Cr2O4 heterostructures for enhanced photoanode performance in dye-sensitized solar cells

The present work focuses on analyzing the structural framework, light absorption behavior, and solar energy conversion efficiency of Nd₂O₃, Sr_0.5Zn_0.5Cr₂O₄, and their 1:1 composite film coated on fluorine-doped tin oxide (FTO) substrates for application in dye-sensitized solar cells (DSSCs). Comprehensive characterization reveals that the composite system exhibits synergistic improvements in material and device performance. X-ray diffraction (XRD) confirms a multiphase crystalline structure with reduced crystallite sizes (7.3–41.0 nm) and elevated lattice strain (up to 0.950%), enhancing dye adsorption and charge transport. X-ray photoelectron spectroscopy (XPS) identifies interfacial interactions, such as Nd³⁺–O–Cr³⁺ bonding that promote electron delocalization and suppress recombination. Atomic force microscopy (AFM) highlights a hierarchical surface morphology with high roughness (Ra = 15 nm) and void volume (53.80 µm³), supporting efficient dye loading and light scattering. Raman and photoluminescence (PL) analyses indicate defect-state formation and efficient non-radiative charge separation. UV–Vis spectroscopy reveals a significantly reduced direct bandgap (2.37 eV) in the composite, enabling broad visible-light absorption (300–700 nm), consistent with an IPCE peak of 80% at 500 nm. Photovoltaic measurements show that the composite photoanode achieves a short-circuit current density (J_sc) of 18.2 mA/cm², open-circuit voltage (V_oc) of 0.676 V, fill factor (FF) of 0.73, and a power conversion efficiency (PCE) of 8.9%, outperforming the individual oxides (Nd₂O₃: 5.90%; Sr_0.5Zn_0.5Cr₂O₄: 7.40%). These enhancements are attributed to type-II heterojunction formation, optimized band alignment, and defect-mediated charge transport. This work establishes the Nd₂O₃: Sr_0.5Zn_0.5Cr₂O₄ composite as a promising photoanode for high-efficiency DSSCs.