Non-Vacuum Fabrication of Bandgap-Controlled CZTGS Alloy Films Using CZTS+CZGS Mixed Nanoparticle Inks

Semiconductor alloy films of Cu 2 ZnSn 1-x Ge x S 4 (CZTGS) were prepared by deposition and sintering of mixed nanoparticle suspensions composed of Cu 2 ZnSnS 4 (CZTS) and Cu 2 ZnGeS 4 (CZGS) nanoparticles with 1-dodecanethiol surfactant. Colloidal CZTS and CZGS nanoparticles were synthesized via the liquid-phase route and used without post-processing treatment. The CZTGS films are crystallized in the form of kesterite structures and form an alloy of CZTS and CZGS without an apparent phase separation. The Sn/Ge ratios in the alloy films were finely controlled by tuning a mixing ratio between CZTS and CZGS nanoparticles. The bandgap energy of the CZTGS film systematically increased from 1.6 to 2.1 eV as the Ge-substitution for Sn in the films proceeded, which indicates the potential of the fabrication method in the manufacture of bandgap-tuned multinary semiconductor thin films.