The Cu Concentration effect on the electro-optical properties of Cu₂ZnSnSe₄ thin films prepared by a non-vacuum solution-based nano-inks process

Cu₂ZnSnSe₄ (CZTSe) nanocrystals (NCs) were synthesized via a coordinating-solvent-based synthesis method using elemental sources. The precipitated NCs were redispersed in toluene to form ink solutions for characterization. The properties of thin films of these inks were investigated as a function of the chemical compositions of the inks. The Cu/(Zn+Sn) ratio of the inks was varied from 0.7 to 1.0, while the Zn/Sn ratio was kept constant at 1. The CZTSe thin film of the ink with a Cu/(Zn+Sn) ratio of 1 exhibited a Cu_2-xSe phase. In addition, the absorption edges of the Cu-poor CZTSe thin films (i.e., the films with Cu/(Zn+Sn) ratios of 0.7, 0.8 and 0.9) were red shifted. Photodetectors (PDs) with a Au/CZTSe/soda-lime glass structure were fabricated. The PD corresponding to a Cu/(Zn+Sn) ratio of 0.70 exhibited excellent photoresponsivity, and its dark current was 7.65×10^-7 A when a bias of 10 V was applied.