Hsing-I Hsiang

Colloidal processing provides a scalable non-vacuum route for fabricating CIGS and CZTSSe thin-film absorbers, but nanoparticle-derived films should be treated as constrained particulate green bodies rather than as simple chemically deposited semiconductor layers. This review reorganizes colloidal chalcogenide photovoltaics using ceramic-processing concepts: ink dispersion, green-body packing, capillary drying stress, ligand burnout, constrained shrinkage, reactive chalcogenization, transient liquid-assisted coarsening, secondary-phase control, defect chemistry, and interface reactions. The central argument is that film densification and grain growth are necessary but insufficient for high-performance CZTSSe devices. Residual carbon, Sn loss, Cu/Zn disorder, ZnSe or Cu_2−xSe secondary phases, excessive MoSe₂, and nonideal absorber/buffer band alignment can dominate open-circuit-voltage loss, fill factor, and carrier collection even when the absorber appears dense in cross-sectional microscopy. By linking ceramic-processing variables to photovoltaic loss mechanisms, this review identifies practical routes for improving colloidal chalcogenide solar cells: controlled ligand exchange and binder burnout, high-green-density precursor design, moderated chalcogen chemical potential, transient liquid management, depth-resolved phase analysis, and integrated front/back-interface engineering.

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.