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Plasma applications on CIGS solar cell processes

Plasma applications on CIGS solar cell processes. Table of contents. Introduction Deposition of CIGS absorber layer CIGS nanoparticle synthesis Printing of absorber layer Results and discussion Application of plasma Densification Selenization Passivation Nanoparticle synthesis

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Plasma applications on CIGS solar cell processes

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  1. Plasma applications on CIGS solar cell processes

  2. Table of contents • Introduction • Deposition of CIGS absorber layer • CIGS nanoparticle synthesis • Printing of absorber layer • Results and discussion • Application of plasma • Densification • Selenization • Passivation • Nanoparticle synthesis • Conclusion

  3. Deposition of absorber layer • Deposition methods • Co-evaporation • Selenization • Low-cost Printing of absorber layer Metal nanoparticle Sintering Selenization Oxide nanoparticle Reduction Sintering Selenization Selenidenanoparticle Sintering

  4. Deposition of absorber layer • Current status • Thesis • Metal, Oxide nanoparticle : over 10% eff. • Selenidenanoparticle : under 3% eff. • ※ High boiling point selenides are not easy to sinter • Company development • Nanosolar : 13.95% • Heliovolt : 12.2% • ※ High-cost process (High-temperature sintering, Hazardous selenization) can be used

  5. CIGS nanoparticle synthesis • Reaction formula: CuCl2+ In2Cl3 + Se + OLA (240℃) → CuInSe2/OLA • 1st attempt : No particle remained after centrifugation 7000rpm/5min • 2nd attempt : Agglomeration during washing/purification • (Insufficient reaction time) • Adjustment : gas inlet/thermocouple location Reaction bath setup

  6. CIGS nanoparticle synthesis Nanoparticles from sputtering • Advantage : Fine nanoparticle <5nm • Equipment : Auto fine coater Substrate bias • Bottom substrate configuration • RF sputtering for chalcogenide target : Conductivity of ionic liquid is not required • Expected disadvantages : • High cost : vacuum process • Low Throughput: low deposition rate of RF sputtering • Composition control may be difficult : low condensation rate of volatile Se RF gun

  7. Printing of absorber layer • Drop casting : Maximum thickness up to 3μm • Film thickness is adjusted by ink concentration • Fast evaporation of solvent induce cracks on film • → Use of high boiling point organic solvent (TCE) TCE CCl4

  8. Device performance Texas Univ. • Open circuit voltage is comparable to vacuum-deposited absorber • Short circuit current and fill factor is low • Factors can be degrade short circuit current : • Low diffusion length • Surface recombination • Grain size • Factors can be degrade fill factor : • Low shunt resistance, High series resistance • Junction roughness KIER

  9. Device performance • Jtotal = Jdiode + Jresistor

  10. Device performance • Ideal diode I-V characteristic does not account for carrier recombination • Carrier recombination increases current in forward bias region

  11. Densification of absorber layer • Example of poor densification

  12. Densification of absorber layer • Rapid sintering process using plasma • Hollow cathode discharge • Microwave-induced plasma • Inductively coupled RF plasma • Extended arc thermal plasma heating • Fast densification : surface cleaning effect • Sintering time ~15 min • Short sintering time reduces loss of Se

  13. Selenization of absorber layer • Metal nanoparticles are easy to sinter • Plasma-assisted selenization : • Low temperature • Fast selenization • Inhibition of hazardous H2Se

  14. Selenization of absorber layer • Inductively coupled plasma is used • Elemental chalcogens sublime in the form of oligomers • (Sn,Sen) • Electronically excited dimers dominate selenium spectra • No evidence corresponding to triatomic sulfur S3 • (λ=374, 378 or 395 nm) or higher chains of sulfur

  15. Selenization of absorber layer • Se+ ion-assisted co-evaporation • Substrate temperature : 500℃ → 350℃ • Deposition on polyimide substrate

  16. Passivation of absorber layer • Low power H implantation (H3+) • No surface degradation or lattice damage • Disappearance of CuS grain

  17. Passivation of absorber layer • Surface : Recombination center • Defects on surface can be passivated by H plasma

  18. Synthesis of nanoparticle • Objectives : Fine,Monodispersed, Large scale • Full vaporization is required • Sufficient length of the processing zone

  19. Synthesis of nanoparticle

  20. Conclusion • Plasma technologies can be applied to all fields of CIGS solar cell processes • Plasma technologies can replace conventional high-cost processes but it is valuable only whenPlasma process is low-cost

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