Establishment Of The Surface Photovoltage System And The Application In Studying The Properties Of Light-induced Carriers In Heterojunctions

The solar cell research has experienced more than half a century. Among them, organic solar cells, organic/inorganic hybrid solar cells and the black silicon solar cells have the advantages of low cost, low reflectivity, but their application is limited by low photovoltaic conversion efficiencis. To find out factors witch limit the photovoltaic conversion efficiencies, surface photovoltage test systems were established to investigate light-induced charge separation and transport mechanisms. In this thesis, the properties of light-induced charge carriers in P3HT/n-Si heterojunction, surface passivation effects of black silicon solar cells and photoelectric properties of P3HT: PCBM bulk heterojunctions were studied uising these systems. Main contents are as follows:1. According to the principle of the test, Kelvin probe based surface photovoltage, modulated surface photovoltage and transient photovoltage systems were setup.2. To figure out the internal factors that limit organic/inorganic heterojunction solar cell efficiency, I selected the P3HT/n-Si heterojunction and analyzed the generation, separation and transport mechanism of the heterojunction using the surface photovoltage technology. There is a "fast" and a "slow" light-induced charge carriers transport mechanism in the heterojunction. Moreover, oxygen and water molecular adsorption in the P3HT layer could induce defect states, and the adsorption is reversible. Finally, transient photovoltage of the heterojunctions with differently thick P3HT layers illustrated that the P3HT/Si interface states would capture partial electrons due to excitons in the P3HT separated at the interface. And this behavior may reduce the efficiency of solar cells based on the structure.3. Due to the very large surface state density of Black silicon solar cells, the surface passivation effects directly affects its efficiency. Since the Surface photovoltage technology is very sensitive to surface states, three kinds of black silicon solar cells:no surface passivation, SiO2passivation and SiO2+SiNx passivation were tested and analyzed using this technology. The electrical characteristics of the solar cells were tested for reference of the photovoltage results. The passivation effects were studied using surface photovoltage technology. we found that the recombination in the bulk and on the surface dominated at shorter times and at longer times respectively from the transient photovoltage results. Surface photovoltage can reveal the generation and recombination mechanisms of light-induce charge carriers, it provides the theoretical guidance to improve the efficiency of the solar cells.4. Although Surface photovoltaic technology has a lot of advantages on the analysis characteristics of light-induces charge carriers of various structures, it is seldom used to study the organic heterojunction. In this work, surface photovoltage technologies were chosen to study the photoelectric properties of organic P3HT: PCBM bulk heterojunctions, and the charge transport mechanisms of the heterojunctions were obtained from the surface photovoltage results. The photovoltage response of the heterojunctions could be affected by P3HT and PCBM mixture ratio, annealing temperature and environmental temperature. Air could greatly reduce the heterojunction photovoltage response and improve the carrier recombination rate. These results imply that surface photovoltage technology is completely competent on the study of photoelectric properties of organic heterojunction.