Nanomatériaux pour application photovoltaïque

Les nanoparticules de Cu2ZnSnS4, (CZTS) offrent une opportunité intéressante pour la fabrication de cellules solaires à bas coût par le procédé impression encres. Divers procédés de fabrication de nanocristaux de CZTS sont développés au cours de cette thèse. Un premier procédé basé sur la polycondensation de complexes ((Cu2+)a (Zn2+)b (Sn4+)c (Tu)d (OH-)e )t+ (Tu = CS(NH2)2, thiourée) permet l'obtention de nanocristaux de CZTS partiellement cristallisés. Un second procédé original de fabrication de nanoparticules mettant en œuvre un gaz dégagé in situ en température comme agent texturant a été développé pour la synthèse de nanoparticules de CZTS hautement cristallisées. Ce procédé a été extrapolé à la fabrication de nanocristaux de CZTS dopé Ga. Enfin dans un troisième procédé, le contrôle de la morphologie des nanocristaux de CZTS a été obtenu dans une voie dissolution re-précipitation. La panoplie de nanocristaux ainsi obtenue devrait être utile à l'optimisation de procédé de fabrication de films de CZTS voie impression d'encres pour cellules solaires bas coût.Copper-Zinc-Tin chalcogenide (Cu2ZnSnS4, CZTS) materials have attracted increasing attention for solar cell absorber layers. To address the issue of low-cost photovoltaic, non-vacuum ink-based approaches were developed involving nanocrystals building blocks. Here, various nanocrystals fabrication process routes are proposed yielding CZTS nanocrystals exhibiting different physicochemical characteristics. A first process is designed to employ a simple sulfide source such as thiourea which advantageously acts both as a complexing agent inhibiting crystallite growth and as a surface additive providing redispersion in polar solvents. We demonstrate the production of solvent-dispersible partially crystallized CZTS nanocrystals via a temperature poly-condensation route involving ((Cu2+)a (Zn2+)b (Sn4+)c (Tu)d (OH-)e )t+ (Tu = CS(NH2)2,thiourea) tailored complex precursors. A second high temperature synthetic procedure performed at higher temperature in molten salts (T > 400 °C) and involving an in-situ generated gas as a template is reported with the objective to minimize defects concentration into the bulk and at the surface of the semiconducting CZTS nanocrystals, Using highly concentrated free SCN--containing reaction mixtures which enhance CZTS precipitation over concurrent reactions, it is demonstrated that this high temperature synthetic route yields highly crystallized CZTS nanocrystals. The versatility of this second process route was demonstrated to the synthesis of Ga doped -CZTS nanocrystals. Lastly, a third process route is reported involving dissolution reprecipitation to the fabrication of CZTS nanocrystals exhibiting platelet morphology. The ability to control crystallinity, morphology and size of the CZTS nanocrystals will provide with an opportunity to further test the effects of these powder characteristics on forming and sintering behaviors of CZTS based films and will greatly help to the further fabrication of low cost solar cells

A general route to the synthesis of surfactant-free, solvent-dispersible ternary and quaternary chalcogenide nanocrystals

A general route to the synthesis of surfactant-free CuInS2 (CIS), Cu2CoSnS4 (CCTS) and Cu2ZnSnS4 (CZTS) nanocrystals dispersible in low boiling point solvents is proposed. These nanocrystal inks should be of great interest to the fabrication of thin film absorbers of chalcogenide solar cells

Highly-crystallized quaternary chalcopyrite nanocrystals via a high-temperature dissolution–reprecipitation route

Quaternary chalcopyrite (Cu2CoSnS4, Cu2ZnSnS4) nanocrystals displaying high crystallization and controlled morphology were synthesized via a high-temperature growth regime achieved by dissolution–reprecipitation of tailored ultrafine precursors in the temperature range 400–500 °C

A high temperature route to the formation of highly pure quaternary chalcogenide particles

A process route to the fabrication of quaternary chalcogenides (Cu2CoSnS4, Cu2ZnSnS4) particles is proposed in molten KSCN at 400 °C. This high temperature route allows the formation of highly pure and highly crystallized quaternary chalcogenides particles. Control of primary crystallites size is demonstrated by altering the chemical homogeneity of the precursors. This method could be exploited to prepare building blocks for the fabrication of low-cost solar cell absorbers

Surfactant-free CZTS nanoparticles as building blocks for low-cost solar cell absorbers

A process route for the fabrication of solvent-redispersible, surfactant-free Cu2ZnSnS4 (CZTS) nanoparticles has been designed with the objective to have the benefit of a simple sulfide source which advantageously acts as (i) a complexing agent inhibiting crystallite growth, (ii) a surface additive providing redispersion in low ionic strength polar solvents and (iii) a transient ligand easily replaced by an carbon-free surface additive. This multifunctional use of the sulfide source has been achieved through a fine tuning of((Cu2+)a(Zn2+)b(Sn4+)c(Tu)d(OH?)e)t+, Tu = thiourea) oligomers, leading after temperature polycondensation and S2- exchange to highly concentrated (c > 100 g l-1), stable, ethanolic CZTS dispersions. The good electronic properties and low-defect concentration of the sintered, crack-free CZTSe films resulting from these building blocks was shown by photoluminescence investigation, making these building blocks interesting for low-cost, high-performance CZTSe solar cells

Surfactant-free CZTS nanoparticles as building blocks for low-cost solar cell absorbers

A process route for the fabrication of solvent-redispersible, surfactant-free Cu2ZnSnS4 (CZTS) nanoparticles has been designed with the objective to have the benefit of a simple sulfide source which advantageously acts as (i) a complexing agent inhibiting crystallite growth, (ii) a surface additive providing redispersion in low ionic strength polar solvents and (iii) a transient ligand easily replaced by an carbon-free surface additive. This multifunctional use of the sulfide source has been achieved through a fine tuning of((Cu2+)a(Zn2+)b(Sn4+)c(Tu)d(OH?)e)t+, Tu = thiourea) oligomers, leading after temperature polycondensation and S2- exchange to highly concentrated (c > 100 g l-1), stable, ethanolic CZTS dispersions. The good electronic properties and low-defect concentration of the sintered, crack-free CZTSe films resulting from these building blocks was shown by photoluminescence investigation, making these building blocks interesting for low-cost, high-performance CZTSe solar cells

A gas-templating strategy to synthesize CZTS nanocrystals for environment-friendly solar inks

A high-temperature gas-templating strategy is proposed to synthesize Cu2ZnSnS4 (CZTS) nanocrystals for all-aqueous solar inks. Our gas templating process route involves the in-situ generation and stabilization of nanosized gas bubbles into a molten KSCN-based reaction mixture at 400 °C. Chemical insights of the templating gas process are provided such as the simultaneous formation of gas bubbles and CZTS nuclei highlighting the crucial role of the nucleation stage on the sponge and resulting nanocrystals properties. The high porosity displayed by the resulting CZTS nanocrystals facilitates their further post-fragmentation, yielding individualized nanocrystals. The advantages of our high temperature gas templating route are illustrated by the following: (i) the low defect concentration displayed by the highly crystalline nanocrystals, (ii) the synthesis of CZTS nanocrystals displaying S2− polar surfaces after ligand exchange. The good photoluminescence properties recorded on the pure CZTS nanocrystals reveal potential for exploration of new complex chalcogenide nanocrystals useful for various applications including photovoltaics and water splitting. Here we demonstrate that using these building blocks, a CZTS solar cell can be successfully fabricated from an environment-friendly all-aqueous ink