Preparation And Surface Photovoltage Properties Of ZnO-based And Si-based Heterostructures

Using solar cell and other photoelectric devices is an effective way for solving the crisis of energy resource and environmental pollution, and for achieving sustainable development. The development of high-performance optoelectronic materials is the basis of effective use of ener-gy. As a typical semiconductor, Si and ZnO have become the research focus of optoelectronics for their excellent optoelectronic characteristics and lower production cost in recent years. Es-pecially, more attention has been focused on their inorganic-organic and inorganic-inorganic heterostructures with compatiblity of the characteristics of different materials, which are believed to be capable of improving the photoelectric performance by enhancing separation efficiency of photo-generated charge and expanding the area of photon absorption. However, the performance of ZnO based heterostructure and Si based heterostructure cannot meet the demand of applica-tion. It is important to do in-depth investigation into the behaviors of photogenerated charges in heterostructure towards improving the photoelectric conversion efficiency and thus realizing larger scales of application. The surface photovoltage (SPV) technique is an effective contactless method for the characterization of semiconductors and structures, which analyzes the behaviors of photo-generated charges. In this dissertation, we prepared several ZnO-based and Si-based heterostructures. The properties of photo-generated charges in heterostructure were systemat-ically studied using SPV techniques. The main content of the dissertation is summerized as follows.ZnO nanorod was prepared by low-temperature hydrothermal method. And then the surface work function changes with illumination were measured and analyzed. Meanwhile, the effects of light incidence direction, surroundings, illumination intensity, and chopping frequency, etc., on the properties of light-modulated SPV were discussed. Then, the different ZnO/PF heterostruc-tures of planar structure and embedded structure were prepared based on ZnO nanorod. We analyzed the reason for the changed surface charges, and illustrated that the more charge separa-tion interface in embedded structure can make the spectral range of photovoltaic response expand and the response intensity increase. Besides, ZnO nanorod/P3HT embedded heterostructure was prepared. We found that P3HT could accelerate the excess carrier transport and change the sur-face free charges in heterostructure. The effects of different chopping frequencies, surroundings and illumination intensity were analyzed on light-modulated SPV in ZnO/P3HT heterostructure. The process of separation and transport for photo-generated charges in the heterostructure was deduced using the phase angle spectra. We then illustrated the mechanism of the photo-generated electron injection into ZnO from P3HT and the direction of photo-generated charge transfer at the P3HT/ZnO/ITO interface.ZnO nanorod/p-Si heterostructure and ZnO film/p-Si heterostructure were prepared by low temperature hydrothermal method and magnetron sputtering, respectively. Using Kelvin probe based SPV measurement system, surface photovoltage response in the heterostructure was in-vestigated systematically. The influences of the ZnO nanorods of different diameters and lengths on the surface photo-generated charges for the ZnO nanorod/p-Si heterostructure, and the influ-ences of thin films of different thicknesses on the surface photo-generated charges for the ZnO film/p-Si heterostructure were respectively studied. The reason of surface photoelectric behavior in heterostructure was preliminarily explored, and we found that the morphology and thickness could change the amount and transfer direction of photo-generated carriers in the heterostrucu-ture.Kelvin probe based SPV, light-modulated SPV and transient SPV were employed to investi-gate the surface photovoltage properties of the spin-coating prepared n-Si/CuPc heterostructure. The influence factors and formation mechanism for surface photovoltage behavior in heterostruc-ture were comparatively analyzed by the effects of different temperature, illumination intensity, chopping frequency, surroundings and thickness of CuPc film. Moreover, by combining with the phase angle spectra, surface photo-generated charge transport mechanisms were described, and illustrated. CuPc films with proper thickness can facilitate the separation and transport of photo-genergated charge in n-Si/CuPc heterostructure.