Optimization Of Preparation And Photoelectric Properties Of ZnO/p-Si Heterojunction

ZnO is a kind of wide direct band gap semiconductor material. The hetero-junction solar cells of ZnO film deposited on the p-Si substrate have been prepared. This ZnO film can emerge window effect and absorb different wavelengths of photon, and then the solar spectrum more will be more used effectively. At the meantime, because the high visible light transmittance of ZnO, and the main absorbed light of silicon is in the region of visible light, a better absorption and conversion of the light independently will occur, then a higher conversion efficiency than silicon cells can be theoretically obtained in ZnO/p-Si hetero-junction solar cells. ZnO raw material is abundant, cheap, and with low growth temperature, high visible light transmittance, non-toxic pollution, thermal stability and chemical stability, and can be easily etched. Since very mature technologies compatible for silicon microelectronics integration has been developed and ZnO will be widely used in solar cell, transparent electrode, optical waveguide device, liquid crystal display and window materials.In this thesis, ZnO films were prepared on silicon substrates by RF magnetron sputtering. Surface grid-shaped electrode and back electrode were prepared and became a simple solar cell. We pay more attention on three sensitive and critical parameters on the structure and photoelectric properties of ZnO films. Their effect on the structure and the solar cell’s photoelectric conversion of ZnO/p-Si hetero-junction has been studied. The main results are listed as follows:1) Within the appropriate thickness, as the thickness increases, the light absorption of the wavelength is less than380nm increases, and light absorption of the wavelength between400nm and800nm decreases.2) If the film is too thin or too thick, the short current will decrease, the IPCE and the photoelectric conversion will both decrease.3) The film with153.0nm sputtered for30min is optimum and its cell properties are the best. Its open-circuit voltage is about114mV and short-circuit current is about203.3μA, maximum power is about5662nW and conversion is about0.12%.4) When the substrate temperature increases, the resistance of the films decreases and the transmittance increases; however, the surface roughness and crystal particle size of the film first increase and then decrease. Similarly, the quantum efficiency and cell properties of solar cell first increase and then decrease. That is to say, the best substrate temperature is350℃.5) The film with substrate temperature of350℃is the best, the structure is most compact, the cell’s quantum efficiency and cell properties are the best. The cell’s short-circuit current is515.3u A, open-circuit voltage is270mV, maximum power is28.3μW and conversion is0.58%.6) The performances of the annealed samples are better than that of the unannealed samples, such as, film’s quality, light transmittance, quantum efficiency and cell properties. It is indicated that the annealing can effectively improve the film’s quality and photoelectric properties.7) As the annealing temperature increase, the crystal particle size of the film increases, c-axis oriented growth of ZnO is first stronger then becomes weak, roughness first decreases and then increases slightly, light transmittance first increases and then decreases, the quantum efficiency and cell properties of the hetero-junction solar cell increases and then decreases. The critical temperature is400℃.8) The structure of the samples annealed at400℃for30min is most compact, that is, the samples have the minimal defects, the highest light transmittance and the highest photoelectric conversion. The cell’s current is1589.0μA and open circuit voltage is194mV, fill factor is0.245, the maximum power is75.57μW, conversion is1.54%, which is more apparently higher than that of the unannealed sample.