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