The investigation of CuxZnSnSe4 bulks with x = 1.4–2.2 for debating the Cu excess and Cu deficiency used in thin-film solar cells

Effects of the Cu variation in CuxZnSnSe4 (CZTSe) bulks with x = 1.4–2.2 on the morphological, structural, and electrical properties has been investigated. Dense CZTSe pellets with grains of 2–5 μm were obtained. All CZTSe pellets showed a p-type behavior with a carrier concentration of 1016–1019 cm−3. CZTSe at x = 1.8 and 2.0 has a high mobility above 25 cm2/V s and an un-favored hole concentration above 1018 cm−3. Although CZTSe at x = 1.6 has a low hole concentration of 1.5 × 1017 cm−3, its mobility is below 2 cm2/V s. The contradiction has made the CZTSe solar cell device with a low efficiency. The explanation, based upon vacancies and antisite defects, for the changes in electrical property is supported by the data from lattice parameter. The study in bulk CZTSe and its defects is helpful as they are applied to the fabrication of thin-film solar cell devices.