Sintering techniques for Low temperature process

1. Sintering techniques for Low temperature process

2. From nanoparticle Ink! CIGS Solar Cell

3. Generally sintering at >500℃ • Se evaporation at high T • Annealing in Se atmosphere • (which is toxic) • Increased cost • Safety issue • Low throughput • Low temperature sintering technique is required Nanoparticle Sintering

4. Challenge in nanoparticle ink sintering “Full densification at Low temperature” Nanoparticle Sintering Sintering Techniques Pressureless Sintering Pressure Sintering Electrically Assisted Sintering (Spark Plasma Sintering, Microwave Sintering) Other Sintering (Plasma Spray Forming, Shock Compaction)

5. Densification Factors for Sintering

6. Densification • C : Constant for a given material under a specific temperature • A : Represents grain packing density, contact, available grain boundary • H : Grain size, shape, intergrain neck geometry • Small nanoparticle & Dense packing increase A Factors for Sintering

7. Coarsening Factors for Sintering

8. Coarsening • K : Represents grain surface mobility • S : System related constant • H : Curvature of particle Factors for Sintering

9. Grain growth → Reduced Grain Boundary Diffusion → Slower Densification • Grain growth has to be suppressed • Particle Packing (Green Density) : A is effected by packing density • Surface Energy : Nano-size particle without agglomeration • Nanoparticle sintering onset temperature (0.2Tm~0.3Tm) • Microparticle sintering onset temperature (0.5Tm~0.8Tm) • Organic removal, Stable phase : Decomposition or phase transformation can • introduce porocity • Narrow particle size distribution : Prevent grain growth • If high green density and temperature control both failed, external driving force is required Factors for Sintering

10. Low temperature • Fast sintering ( 5-20 min. ) • Hot Pressing • Hot Isostatic Pressing • - High cost of equipment • - Pressure limit • Sinter forging • - Not effective for <20nm nanoparticles • - Shear stress Hot Pressing Pressure Sintering Hot Isostatic Pressing

11. Fast sintering ( 5-20 min. ) • High quality, uniform sintering • High Reproducibility • High thermal efficiency • 2~20kA DC current • few V voltage • 30~200 Mpa • Expensive equipment • Sintering condition has to be • readjusted for each materials • Low throughput Spark Plasma Sintering

12. Fast heating • Lower sintering temperature • (Due to volumetric heating) • Fast sintering • Selective heating • Full densification is hard to achieve • Difficult to measure and control temperature • Non-uniform heating Microwave Sintering

13. Forming and sintering in one step • Short sintering time • Suppression of grain growth • Pancake shaped grain • Difficult to produce thick samples Plasma Spray Forming

14. Very high pressure in milliseconds time • Plastic deformation and melt induced bonding • Fine grain • Shockwave produce defects • Inhomogeneous stress • Difficult to apply into hard materials Dynamic Compaction

15. 20nm size nanoparticle • 250W Plasma (160℃, 5min) • Poor densification was reinforced by silica binder • Microstructure comparison was not presented Arc Plasma Sintering Y. Ito et al. JJAP 47, 8 (2008)

16. Spin-coated ZnOnanorod • Annealed at 270℃ with zinc acetate solution Precursor Solution Sintering B. Sun et al. JPPC 111, 18831 (2008)

17. Novel Sintering Technique • - Microwave Sintering • - Arc Plasma Sintering • - Precursor Solution Sintering • Dense Nanoparticle Packing Methods • Nanoparticle Synthesis Futurework