Preparation And Energy Band-gap Calculation Of CuInS₂ And CuIn_1-xGa_xS₂ Photoelectric Materials

With the emergency of energy crisis, people were forced to seek new energy source. Solar energy, which is inexhaustible and pollution free, has aroused people’s attention. CuInS2 is semiconducting material with direct band gap about 1.50eV. It matches well with solar spectrum, has large absorption coefficient and high conversion efficiency, and it has good stability. Doping element Ga in CuInS2 makes CuIn1-xGaxS2, whose band gap width changed with different amount of Ga, which can be used to seek better solar energy absorption. CuIn1-xGaxS2, as absorbing layer material of solar cell, is non-toxic, low-cost, and has a very good prospect.In this paper, we used VASP software to calculate the energy band gap width of CuInS2 and CuIn1-xGaxS2 under PBE pseudo potential, using the spin-coating chemical co-reduction to prepare CuInS2 and CuIn1-xGaxS2 films. Results were observed and analyzed by X-Ray diffraction (XRD), scanning electron microscope (SEM), Energy Dispersive Spectrometer (EDS) and ultraviolet visible spectrophotometer. The paper studied the effects of different materials and processes on the films morphology and properties. The main content of this paper are:Calculated the bang gap width of CuInS2 and CuIn1-xGaxS2 with concentration of element Ga 1/4,1/2,3/4 and 1.0. Convergence test and lattice optimization were carried out to determine plane wave cut energy (ENCUT), K spatial grid (K-mesh) and lattice constants. The effects of element Ga on unit cell volume and band gap was studied. The results showed that the unit cell volume and band gap of CuIn1-xGaxS2 were influenced only by atomic content of Ga, not affected by doping position. With the increasing of Ga, the unit cell volume decreases and band gap increases.CuInS2 films were prepared by spin-coating chemical co-reduction. The effects of holding time, reaction temperature, reaction times, sulfur source and solvent were studied. The results showed that the longer holding time, higher reaction temperature and the increased number of reaction will promote crystallization. But when holding time was over 20 hours, crystallization changed slightly. Thiourea was proved to be the proper sulfur source because the diffraction results and crystallinity with preferential growth on (112) crystal surface were best. C2H5OH as solvent can make films better diffraction results and crystallinity than C2H7NO and C2H8N2.Use the spin-coating chemical co-reduction to make CuIn1-xGaxS2 films. The effects of holding time, reaction temperature on films, and effect of Ga concentration on diffraction results and bang gap were studied. The results showed that the temperature with best diffraction results and crystallinity between 180～220℃ was 200℃. With the increasing of Ga, the diffraction peak moved to the right and decreased, and crystallinity was worsen. The estimated band gap based on extrapolation became larger.