Structural, optical and electrical properties of Cu₂FeSnSe₄ and Cu(In,Al)Se₂ thin films

Cu-based semiconductors Cu₂FeSnSe₄ (CFTSe) and Cu(In, Al)Se₂ (CIAS) have been fabricated using radio-frequency magnetron sputtering combined with rapid thermal selenization processing. For CFTSe, the heating rate ranging from 60 to 150 °C/min results in a difference in structure, morphology and optical properties. Thin film exhibits a pure phase structure, smooth surface and a band gap of 1.19 eV as the heating rate elevated to 90 °C/min. Furthermore, the CFTSe thin film selenized at 90 °C/min own the smallest value of cell volume compared with the others samples, which represents a more stable structure. In terms of the other Cu-based material CIAS, three different selenization pressures, i.e., 1, 5 and 10 Torr, have been employed for CIAS preparation. Thin film transforms into single phase with dense morphology along with the pressure of 1 Torr. The diverse band gap of CIAS thin films from 1.34 to 2.18 eV attribute to two reasons: (i) the various Al content will affect the hybridization degree of Al-Se, and finally tunes the band structure, (ii) amounts of CuSe has a certain degree of effect on the band gap of the CIAS. In addition, the electrical properties of CFTSe and CIAS are also researched with the open circuit voltage (V_oc) of 94 and 365 mV, respectively, signifying potential applications of CFTSe and CIAS for the thin film solar cells.