Synthesis and characterization of Ge doped Cu2ZnSn(S,Se)4 bulk in the presence of reactive liquid phase sintering aid

The quaternary chalcogenide Cu2Zn(Sn1-xGex)(S,Se)4 bulks, where x is Ge/[Ge+Sn] molar ratios of 0, 0.15, 0.30, and 0.45 were synthesized via reactive liquid phase sintering at 600 °C for 30 min in the tube furnace and characterized systematically. Together with Sb2S3 as a reactive liquid phase sintering aid, the effects of Ge incorporation on densification, grain boundary, crystal phase purity, crystalline size, and electrical properties were studied. The morphology of the resulted Cu2Zn(Sn1-xGex)(S,Se)4 bulk was found to be more densified and compacted at Ge/[Ge+Sn] molar ratio of 0.15 compared to the rests. The X-ray diffraction peaks were shifted towards a higher angle as Ge fraction was increased. The hole concentrations for the entirely p-type bulks were determined to be 3.67 × 1018, 1.40 × 1018, 1.28 × 1018, and 8.90 × 1017 cm−3 at Ge/[Ge+Sn] molar ratios of 0, 0.15, 0.30, and 0.45, respectively. The effects on conductivity and mobility were consistent with their interrelations. Hence, the synthesis and study of Ge incorporated Cu2ZnSn(S,Se)4 bulk using powder technique allows identifying the composition which is expectedly more important for the fabrication of thin film solar cells.