A Study On The Photoelectric Behavior Of Functional Materials By Transient Photovoltage Technique

The organic, inorganic functional materials have been widely used in the electronic, optical and optoelectronic semiconductor devices as well as the photocatalysis. The performance of the devices as well as the photochemical reactivity of photocatalyst is directly related to the optoelectronic properties of the semiconductor materials. Therefore, the understanding of the photo-generated charge carriers properties is very important for theoptimization of the devices performance and the photochemical reactivity. As a result, the study of the photo-generated charge carriers properties is one of the most active researches at present. The nondestructive characterization and qualification of semiconductor materials as well as the devices is a crucial step in the fabrication of modern day electronic, optical, and optoelectronic semiconductor devices. Improvements in the quality and yield of semiconductor devices, with a resultant increase in performance and reduced cost, will rely on characterization methods that are informative, nondestructive, convenient, easy to use, and inexpensive. A photovoltage arises whenever photo-generated charge carriers are separated in space. Therefore, we can obtain the fundamental properties of light absorption, transport of excess carriers in a semiconductor material and the electronic structures of the surface and interface from the study of the surface photovoltage (SPV). The measurements of the photovoltage do not need the Ohmic contact between the measured sample and the electrode and may be performed under different atmosphere and temperature. In addition, the high sensitivity of SPV for the detection of the surface charge makes it be a powerful method to characterize the semiconductor materials and devices.Based on the establishment of the transient photovoltage which may detect the evolution of the SPV with the time, the present thesis is successful to the study of the photoelectric properties in various functional materials using the transient photovoltage technique. The results in this paper provide the theory evidence for optimization of the performance of the semiconductor devices, dye-sensitized solar cells, and for improvement of the photochemical reactivity of the photocatalyst and the light emission quantum yield of the luminescence materials. And the light source (laser pulse) was extended to the continuum visible light, the information about the time resolution of photo-generated charge carriers in the functional materials and devices have been attained further.The main results are illuminated as follows:1. Transient photovoltage technique has been applied to investigate the behaviors of the photo-induced charge carriers in bulk semiconductor materials (include the n- and p- type of Si single crystal as well as the TiO2 single crystal with various crystal plane (110, 001, 111)). The results indicate that the transient SPV directly reflects the optoelectronic properties of the semiconductor surface. The factors, as the surface charge region, the density of the surface states, etc., that may influence the SPV response in the bulk semiconductor have been discussed.2. The study of the photoelectric properties of the nanoscale functional materials, which include the TiO2 nanoparticle, disorder and ordered nano-TiO2 film. It was directly observed the photo-generated charge carriers drift at TiO2/ITO interface and the diffuse in the TiO2 film, which demonstrates the existence of the potential barrier at the interface. The relation between the SPV response and incident light under different transport dynamic mechanism was discussed. These results provide a new experiment for the understanding of the work mechanism of the dye-sensitized solar cells.3. The photovoltaic properties of Fe3O4@Fe2O3 nanoparticles have been investigated by the surface photovoltage spectroscopy and transient photovoltage technique. The effect of the junction formation in the Fe3O4@Fe2O3 nanoparticles on the separation, transport and recombination of the photogenerated charges have been discussed in detail. These results are helpful in understanding the photovoltaic properties of nanoscaled materials with such structure. Through investigating this system, we can design and construct the specific interface structures, which can be applied to photocatalysis and photodegradation based on the behavior properties of the photogenerated charges.4. The photovoltaic properties of a series of the porphyrin compounds have been investigated by the transient photovoltage technique. We intend to construct the interface between the porphyrin film and the ITO substrate, and investigate the effect of the junction on the behaviours of the photogenerated charge. The reversal of the photovoltage polarity under the effect of the interface, as well as the change of the time in two kind of response process with the variety of the intensity of the incident illumination was observed. The results provide the scientific experiment fact for understanding the work mechanism of the semiconductor devices made from the organic semiconductor films, such as the organic light emitting diodes (OLED). Also, the results may provide the theory evidence for the design of the high performance optoelectronic devices.