Studies On The Photoelectric Properties Of Different Semiconductor Materials And Correlated Composites

Photoelectric material is the basis of solar cells, which is the key to provide reliable clean energy for the human society. In order to get higher photoelectric conversion efficiency and more reliable use, the research and development of photoelectric materials is an important task for scientific research workers now.Cu₄Bi₄S₉?CBS? exhibits excellent optical stability, broad optical absorption, and superior photoelectric properties. However, pure CBS suffers from short hole-diffusion length and high electron-hole recombination rate, inhibiting its promising applications as electron donor. Reduced graphene oxide?RGO? or graphene is a crystalline allotrope of carbon with a two-dimensional?2D? structure, in which carbon atoms are packed densely in a regular sp2-bonded atomic-scale hexagonal pattern. Due to its unique structure?atomic thick carbon layer? and properties, such as remarkably high electron mobility at room temperature, high specific surface area, high thermal conductivity, etc., we attempt to improve the separation of photogenerated charges in CBS with incorporation of RGO. ?-Fe₂O₃ is especially attractive as electron acceptor due to its stability, abundance, cost effectiveness, as well as suitable band gap and valence band edge position. ?-Fe₂O₃ has a great prospects of application in the field of photovoltaic material. In our study, we had a in-depth exploration for several kinds of materials.The research content of this paper mainly has the following three aspects:In chapter 2 of this paper, the development and the basic principle of surface photovoltaic technology are detailed. At the same time, this chapter introduces the basic structure of the test system of surface photovoltage spectrum and the function mechanism of each part of the test system. The technologies of the testing for the surface photovoltage are also expounded in this section. At the end of this section, the electric field induced surface photovoltage spectroscopy is discussed in detail. By the study of this chapter, we can understand adequately the mechanism of surface photovoltage technology and the main methods of testing for semiconductor materials.In chapter 3 of this paper, For the synthesis of heterojunction, ?-Fe₂O₃ sol was deposited onto ITO by a spin-coating method. Different CBS-RGO were prepared by incorporating RGO into CBS colloid with various RGO. By using X-ray diffraction?XRD?, scanning electron microscope?SEM?, high-resolution transmission electron microscopy?TEM?, selected area electron diffraction?SAED?, and surface photovoltage spectroscopy?SPS?,the samples were analyzed carefully to get the effect of graphene for Cu₄Bi₄S₉ and the mass ratio of graphene with the best photoelectric.In chapter 4 of this paper, For the synthesis of heterojunction, ?-Fe₂O₃ sol was deposited onto ITO by a spin-coating method. Then CBS and CBS-RGO were spin-coated onto ?-Fe₂O₃ to fabricate ?-Fe₂O₃/CBS and ?-Fe₂O₃/CBS-RGO heterojunctions. ?-Fe₂O₃/CBS and ?-Fe₂O₃/CBS-RGO heterojunctions were studied by using X-ray diffraction?XRD?, scanning electron microscope?SEM?, surface photovoltage spectroscopy?SPS? and Electric field induced surface photovoltage spectroscopy?EFISPS?. The I–V characteristics of cells were measured under illumination with a sun simulator at AM 1.5. ?-Fe₂O₃/CBS-RGO exhibits a higher SPV and more obvious amalgamation between two response regions than ?-Fe₂O₃/CBS. So we can come to a conclusion that the defect of the high electron recombination rate was overcame by adding RGO, improving the the separation efficiency of photogenerated charges and generating a higher SPV. By the transport mechanism of photogenerated charges, there are the energy level matchings among different components?CBS and RGO, RGO and ?-Fe₂O₃, CBS and ?-Fe₂O₃? in the ?-Fe₂O₃/CBS-RGO heterojunction. Therefore, the photogenerated electrons in CBS can transport to RGO?or directly to ?-Fe₂O₃? and then quickly to ITO electrode. According to the EFISPVs, the separation efficiency of photogenerated charges of ?-Fe₂O₃/CBS-RGO was improved largely. However, the separation efficiency of photogenerated charges of ?-Fe₂O₃/CBS was not improved largely. Therefore, The conclusion of this experiment is a further evidence that the grapheme plays an important function in the separation of photogenerated charges. The highest efficiencies ?-Fe₂O₃/CBS–RGO and ?-Fe₂O₃/CBS cells are 6.8% and 3.1%, respectively.The I–V characteristics further demonstrated the comprehensive effect of energy levelmatching, RGO conductivenet- work and other factors on the separation of photogenerated charges.