Investigation of a novel intermediate band photovoltaic material with wide spectrum solar absorption based on Ti-substituted CuGaS2

Intermediate band solar cells (IBSC) have been proposed in order to substantially increase the efficiency of solar cells. A novel intermediate band (IB) photovoltaic material of Ti-substituted CuGaS2 (Ti-CGS2) has been successfully fabricated via a facile solvothermal method. By part substitution of Ga atoms with Ti in the CGS2 chalcopyrite crystal, a narrow partially filled IB was introduced and two additional absorption bands at 710 nm (IB → CBM, 1.75 eV) and 1350 nm (VBM → IB, 0.92 eV) were directly observed in the UV-vis-NIR spectrum. Element Ti, acting as trivalent substituents confirmed by the X-ray photoelectron spectroscopy (XPS), forms an IB from the lowest subshell of its 3d levels. Photoelectrochemical investigations of the Ti-CGS2 verified the wide-spectrum solar response from the IB effect. This material leads to lower-energy photon absorption, which could be a promising candidate for the high-efficiency solar cells.