Ag‐Assisted Microstructural Optimization of Nanoparticle‐Derived CZTSSe Thin Films

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Abstract
Ag‐substituted (Ag x Cu 1 − x ) 2 ZnSn(S,Se) 4 absorbers were prepared from nanopowder‐derived precursor films by pressure‐assisted pre‐sintering and selenization. This study examines Ag substitution as a processing‐active additive in nanoparticle‐derived kesterite absorbers, where particle packing, interparticle necking, chalcogen exchange, constrained shrinkage, and fine‐grained‐layer formation govern the final film quality. Ag incorporation expanded the kesterite‐related lattice, shifted the x‐ray diffraction peaks to lower angles, and increased the ordering‐sensitive I (101)/ I (112) ratio from 1.8% to 7.3%. More importantly, Ag accelerated microstructural development during selenization, promoted grain coarsening, improved through‐thickness densification, and reduced the fine‐grained bottom layer commonly observed in nanoparticle‐derived CZTSSe films. The optimum Ag/(Ag + Cu) ratio was 10%, which enhanced grain growth while avoiding the Ag‐rich surface segregation observed at 15% Ag. This composition showed the lowest resistivity of 1.42 Ω cm, improved carrier mobility, and a moderate optical band gap of 1.05 eV. The corresponding device efficiency increased from 0.5628% for CZTSSe to 0.7243% for 10% Ag‐substituted ACZTSSe, mainly through improved open‐circuit voltage and fill factor. These results indicate that moderate Ag substitution can regulate the high‐temperature conversion pathway of nanoparticle‐derived CZTSSe absorbers, providing a processing‐oriented strategy for improving densification, microstructural uniformity, and transport continuity.

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