Synthesis of titanium-doped CdIn2S4 thin film and its photoelectric properties for intermediate band solar cells

The series Titanium-doped CdIn2S4 (Ti-CIS) thin films, with a spinel structure, were successfully synthesized by a typical technology of magnetron sputtering. The prepared Ti-CIS thin films were characterized by X-ray diffraction patterns, Raman spectrometer, energy dispersive X-ray analysis, transient photocurrent response and UV–vis–NIR spectrophotometer. The experimental results demonstrated that the optical absorption spectra were widened in Ti-CIS films. Due to Ti doping, two additional sub-band edge responses were observed at about 760 nm (1.63 eV) and 1150 nm (1.07 eV), which indicated a partially filled intermediate band (IB) was formed in the forbidden band of Ti-CGS3 film by the spin-up t2 g states, and leaded to lower-energy photon absorption. Whereas, no additional sub-band edge responses were obviously observed in the optical absorption spectra of the Ti-CIS1 and Ti-CIS2 films, probably because of the Ti-CIS films inferior in quality or less doped-Ti content. The result analysis of the transient photocurrent response further verified that a larger number of carriers are generated in the Ti-CIS films, the surface recombination process rarely occurs. In general, the good photoelectric properties of Ti-CIS films prepared by magnetron sputtering expected to be a promising candidate IB material for the high-efficiency thin film solar cells.