太阳能电池研究现状.docx

1、太阳能电池研究现状太阳能电池研究现状Activity and Current Status of R&D on Space Solar CellsINTRODUCTIONThe Japan Aerospace Exploration Agency (JAXA ), the former National Space Development Agency of Japan (NASDA), had concentrated solely on the development of silicon space solar cells until the year 2000. With the ne

2、ed for higher-efficiency solar cells in space , JAXA began developing IIIV multi-junction (MJ ) space solar cells in 2001. Two types of high-efficiency triple-junction (3J) solar cells have been developed. These cells are fabricated using epitaxial wafers grown by companies in the United States and

3、have an average efficiency of 28% or higher at the beginning-of-life (BOL).For the newly developed 3J cells to be used for space missions, however, it was also necessary to collect radiation tolerance or end-of-life (EOL) data. Accordingly, irradiation tests have been conducted to study radiation de

4、gradation behavior of the 3J cells using various types of accelerators in the Japan Atomic Energy Research Institute (JAERI) at Takasaki as part of JAXAJAERI collaboration activities.A number of basic studies on component sub-cel ls in a 3J cell have continued to further improve MJ cell performance.

5、 One such study attempts to clarify the dependency of radiation degradation trends of IIIV single-junction solar cells on their structure or environmental conditions to under stand the degradation mechanisms of MJ cells. A flight demonstration experiment of an InGaP/ GaAs solar cell and ground irrad

6、iation tests were completed in another study. The results will be applied to develop a solar cell device simulator, which should enable predictions of EOL performance of any MJ cell structure .A copper indium gallium diselenide(CuInG aSe2(CIGS) thin-film sol r cell is a promising candidate for futur

7、e thin-film space solar cells since the cells not only have the potential to achieve higher conversion efficiencies than other thin-film solar cells, but also show possess super radiaion tolerance.In addition, the CIGS thin-film solar cells have superior properties, such as low costand light weight,

8、 because the cells can be formed on polyimide or metal foil substrates. A flight demonstration experiment of the CIGS solar cells was per-formed ,and ground irradiation tests were conducted to investigate the mechanism s of the super ion radiation tolerance.This paper describes R&D activities in Jap

9、an on space solar cells. The results of the activities are described.IIIV MULTIJUNCTION SOLAR CELLTriple-jun ction cell developmentTriple-junction cells have been developed under contracts with Sharp Corporation. These cells are made of epitaxial wafers produced in the US; however, a new anti-reflec

10、tion coating has been designed. Figure 1 depicts the typical current voltage (IV) characteristic under AM0, 1 sun simulated light illumination. An average efficiency exceeding 27% has been achieved. The quantum efficiency (Q E) of the top cell is designed to be relatively low in order to improve EOL

11、 current output.Radiation response of a triple-junction cell The newly developed 3J cells were subjected to proton irradiation tests with proton acceleration energy varying from 30 keV to 10 MeV. Figure 2 illustrates typical degradation trends of: (a) open- circuit voltage Voc; (b) short-circuit cur

12、rent Isc; and (c) maximum power Pmax as a function of proton energy selected in the experiment.Relative damage coefficients (RDCs ) are defined at a remaining factor of 80% for Pmax and 90% for Voc and Isc from the degradation curves obtained, and the RDC is indicated in Figure 3. The RDC of Voc exh

13、ibits three energy maxima around 30 keV, 250 keV and 2 MeV. When protons are accelerated with these energies, the proton ranges agree with the depth s of p n junctions of the three sub-cells according to the TRIM calculation.Because Voc of a 3J cell is the sum of generated voltages from constituent

14、three sub-cells, Voc is directly influenced by damage to each sub-cell. Therefore, Voc degradation of a 3J cell strongly depends on both the cell structure and the range of the irradiated protons where the density of induced defects is considered to be maximized.To better under stand 3J cell degrada

15、tion, the degradation trends were replotted as a function of the displace-ment damage dose Dd.This methodology is also useful for degradation prediction in an actual space environ-ment. Figure 4 presents the results. For Voc(Figure 4a), the degradation is found to split distinctly into two curves. T

16、he upper curve consists of data of energy less than 100 keV and the lower one refers to 150 keV or higher. According to the TRIM calculation,the upper curve represents degradation of only the InGaP top cell,and the lower one involves the InGaP top and the GaAs middle cell degradation. Since the cont

17、ribution of the Ge bottom cell Voc to the 3J Voc is small, the third curve cannot be observed. In the case of Isc(Figure 4b), all data fit on a single curve, except a few anomalous points corresponding to severe degradation in the Ddrange of 12 *1011MeV/g . These Dd values are consistent with a prot

18、on irradiation of 150380 keV at a flux range of 1012cm-2. As a result, for Pmax(Figure 4c), the degradation trend is expressed with two curves and a few anomalous points.Figure 2. Degradation of: (a) Voc; (b) Isc; (c) Pmax of a 3J cell as a function of proton flux for various proton energiesThe QE o

19、f the 3J cell were investigated to estimate Isc of each sub-cell after irradiation. Figure 5 exhibits typical change in QE of the top and middle cell in a 3J cell due to proton irradiation. The QE data of the Ge bottom cell are omitted because the current output of the bottom cell does not affect th

20、at of a 3J cell (Figure 6).Numerical convolution of the AM0 solar spectrum with the QE data provides the relative Isc for the specific sub-cell. Figure 6 illustrates Isc degradation of the InGaP, GaAs and Ge sub-c ells as functions of proton energy and flux. For comparison , measured Isc value s of

21、the 3J cell are also plotted in the figure. When proton fluence is less than 1011cm-2, the InGaP top cell is consider ed to limit the Isc of the 3J cell over the entire energy region.After irradiation with energies between 150 and 380 keV at a fluence of 1012cm -2, however, Iscof the GaAs middle cel

22、l is significantly decreased, and the GaAs cell becomes the current-limiting cell. This means that the current-limiting cell changes due to specific proton irradiation conditions. This is also why the anomalous degradation points were observed in Figure 4(b) . In addition, since the established empi

23、rical equation used to describe a degradation curve is based on single-junction cells, it cannot accurately express the Isc degradation characteristics of a 3J cell that involves the current-limiting cell change phenomena in higher-fluence regions.Space demonstration of a dual-junction cellThe perfo

24、rmance of a 3J cell is almost totally governed by that of the InGaP top cell and the GaAs middle cell because the contribution of the Ge bottom cell is small. The radiation response of an InGaP/ GaAs dual-junction(2J) solar cell (BOL efficiency 24 5% under AM0, 1 sun) was demonstrated by Mission Dem

25、onstration-test Satellite No.1 (MDS-1 ) Tsubasa , which flew in a geostationary transfer orbit (GTO).The 2J cell is originally designed for terrestrial use, therefore, the InGaP top cell is relatively thicker than the same cells for space applications. Three cells were connected in parallel to adjus

26、t the current output to the measurement range. A pair of three-cell sets was prepared, and 500- or 100- mm-thick radiation-shielding cover glasses were attached to each of the sets. The mission duration was approximately 600 days after launch. The GTO cuts across the inner and outer Van Allen Belts

27、so that the MDS-1 was exposed to a much more severe radiation environment than in cases of a low-Earth orbit (LEO) or a geostationary orbit (GEO).The I V characteristic s of the 2J cell were successfully collected from the beginning to the end of the mission,and the current and voltage values were c

28、orrected for voltage shift caused by the measurement circuit, temperature, angle to the Sun, and solar irradiance (distance between the Sun and the Earth). Figure 7 presents the remaining factors of Isc, Voc and Pmax against the mission elapsed time (MET) in days after launch obtained for the entire

29、 mission duration. In the case of Pmax, a fitting I V curve was calculated first, and then the Pmax value was obtained. Th e first data at a MET of 2 days after launch were used as the initial value s. The change in degradation rate appearing from the trends was confirmed to come from the change in

30、the radiation flux in orbit due to solar flares according to the data from the radiation dose monitors installed on the satellite . Although the 2J cell was designed for terrestrial use, the cel ls have sufficiently high remaining factor s for space use; the remaining factor at the end of mission du

31、ration was 76% for Isc, 88% for Voc and 64% for Pmax.Prior to the launch, ground irradiation tests were conducted at JAERI, Takasaki on the 2J cell as well as its InGaP top and GaAs bottom cells with 1 MeV-electrons and 10 M eV-protons. The results are described elsewhere .An equivalent 1 MeV electr

32、on flux was estimated for the mission environment using the ground test results. The fluences corresponding to the remaining factors at the end of the mission of Isc are 1.1*1015cm-2; Voc7.0*1015cm-2; and Pmax1.3*1015cm-2. The equivalent fluence of Voc is about one order of magnitude greater than th

33、at of Isc and Pmax. An equivalent 10 MeV proton fluence was estimated in the same way, and the fluence was 1.2*1013cm-2 for Isc,7.0*1012cm-2 for Voc and 5*1012cm-2 for Pmax. In this case ,the fluence agree relatively well, presumably due to the proton-rich radiation environment in orbit. Table I summarizes the results.F