Spray and inkjet fabrication of Cu2ZnSnS4 thin films using nanoparticles derived from a continuous-flow microwave-assisted synthesis

Patterning of kesterite (Cu2ZnSnS4 or CZTS) thin films by the inkjet printing technique has been demonstrated for the first time. For the ink formulation, CZTS nanoparticles were obtained in large quantities using a continuous-flow synthesis based on microwave-assisted heating of a mixture of mercaptoacetic acid, sodium sulfide, tin chloride, copper and zinc acetates dissolved in water. For the further formulation of a stable nanoparticle ink with rheological and wetting properties suitable for inkjet pattering on Mo/SLG substrates, a mixture of methyl-ethyl-ketone (MEK) and dodecanthiol (DDT) with the volume ratio MEK:DDT=9:1 was used as a solvent. It has been shown that the same ink can be successfully used for the preparation of thin films by spray-coating technique. Deposition of the nanoparticle ink by both methods followed by annealing at 540 °C in a sulfur-containing atmosphere allowed obtaining crystalline thin films of kesterite with the desired (copper poor and zinc rich) chemical composition. The process developed in the present study is promising for a low-cost non-vacuum production of thin films of CZTS which is expected to serve as a substitute for the solar absorber materials based on rare and toxic elements.