Research On Spectral Solar Photoelectric Conversion System

Considerable progresses have been made in the solar cell researches and applications since BELL Laboratories invented the world's first solar cell of about 6% efficiency in 1954 in United States. The photoelectric conversion efficiency of the present third-generation solar cells, the multi-junction (laminated)ones has been raised into nearly 43% on the basis of the first generation of silicon solar cells and the second generation of thin-film solar cells. However, with the improvement of the conversion efficiency, research and development of the multi-junction cells has met problems due to the limitations of device production technology. More layers (junctions) need to be added within the cells in order to match the more widely distributed solar spectrum and absorb more solar energy; however, such an increase in layers (junctions) will consequently increase the cell thickness and thus lead to more energy loss related with light penetration. According to calculation, the photoelectric conversion efficiency of the multi-junction solar cells could hardly break through 50%.To overcome the bottleneck problems of the multi-junction solar cell technology, researches on the spectrum splitting solar cells have been widely conducted in recent years. A new multi-cell combination is reported to have reached efficiency of 43�1.5% under the conditions of solar concentration, according to the latest research results of University of South Wales, Australia in 2010. With optimistic anticipation, scientists will develop a new pattern of solar cells based on spectrum splitting theories in the near future, and the cells'photoelectric conversion efficiency could by that time reach or even exceed 60%.This paper mainly studies two key aspects of the spectrum splitting solar photovoltaic system:1, splitting devices of the solar spectrum; 2, the solar cells'photoelectric conversion characteristics which could match the spectrum splitting. 1, Splitting devices of the solar spectrumOptical filters could be used to achieve high efficiency in splitting solar spectrum, with notice of different spectral response characteristics of solar cells. Based on the design principles of conventional spectral filters, we have amended the classical interference formula of thin-film optical filters, and provided a new analytical formula of thin-film reflective coefficients which concerns the spatial interference effects as well. Moreover, we have proved the formula with theoretical consideration of three kinds of physical limits. For the experiment, we used plasma-assisted e-beam evaporation deposition equipment to produce SiO2 films in different thicknesses as samples. And then we adopted the elliptical polarization spectroscopy methods. By continuously changing the incident angles, we have verified that the new optical thin-film formula which takes spatial interferences into consideration does match the calculation results. The results also demonstrate this new formula for optical thin-film devices has a broader application scope, which would contribute to the design, production and application of optical thin-film devices,e.g. the complex-structural high-performance spectrum-splitting filter film.2, The solar cells'photoelectric conversion characteristics which could match the spectrum splitting.According to the solar spectrum splitting requirements, we set up a few photoelectric conversion test systems of different spectrum-splitting solar cells, including experimental devices for condensing lens, solar energy transmission and acquisition, optical filters and battery coupling, photoelectric conversion efficiency detection and so on. And then by comparing the advantages and disadvantages of different IV test circuits, we designed and set up a new IV test system for the experiment. With the IV test system, we tested and recorded the changing photoelectric conversion efficiency of the multi-spectral solar cells, while the testing solar radiation was changing from 0.5 to 6.0 SUN(AM1.5G). By a large number of data analysis, we found a maximum conversion efficiency of 35.8% under the radiation condition of 2.8 SUN(AM1.5G). Moreover, through a variety of IV analysis, including analysis on changes of the photocurrent, and internal resistances in both series and parallel circuits following light intensity changes, we estimate that under the best industrial production conditions, the multi-spectral solar cell conversion system will reach a maximum efficiency of 46.65% under the radiation condition of 3.8 SUN(AM1.5G). Based on the research results, we would subsequently offer some advice on how to produce high-efficiency combined type spectrum splitting solar photovoltaic system.