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2021-06-18T13:40:31+09:00
2021-06-18T13:40:31+09:00
2021-06-18T13:40:31+09:00
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Ritsumeikan Univ.KO-407
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1 g
10 36 574.5 780 re
f
BT
0 g
/TT0 1 Tf
14.25 0 0 14.25 64.3272 788.25 Tm
(High-efficiency Spherical Si Solar Cell with Semi-light-concentration Sy\
stem)Tj
/TT1 1 Tf
12 0 0 12 463.0059 759.75 Tm
(Chikao OKAMOTO)Tj
-34.875 -2.313 Td
(Si spheres that are the substrate of spherical Si solar cells can be dir\
ectly produced from melt Si without)Tj
-1 -1.5 Td
(cutting and polishing processes where Si material loss occurs in Si wafe\
r production process. Moreover,)Tj
0 -1.5 TD
(spherical Si solar cells with semi-light-concentration system can reduce\
the Si quantity, because spherical Si)Tj
T*
(solar cells are arranged in sparsity. Therefore, the spherical Si solar \
cell with semi-light-concentration system)Tj
T*
(was expected to lead the further cost reduction. In this paper, we discu\
ssed the fabrication of spherical Si)Tj
T*
(solar cells with semi-light-concentration system, electric and crystallo\
graphic characterizations of spherical Si)Tj
T*
(solar cells based on Si spheres with a diameter of 1 mm produced by a dr\
opping method, and high-efficiency)Tj
T*
(technology of the spherical Si solar cell.)Tj
1 -2.5 Td
(The crystal growth of the Si sphere produced by the dropping method is c\
ompleted in the fall duration of)Tj
-1 -1.5 Td
(about 2s. The crystal growth of the Si sphere, which is different from t\
he crystal growth of the single-crystal)Tj
T*
(Si ingot, is the seedless and high-speed cooling. Therefore, during the \
dropping, the generation of many)Tj
T*
(crystal nuclei in the Si sphere occurs, and then the crystal growth of t\
he Si sphere occurs in arbitrary)Tj
T*
(directions. As a result, the Si sphere is generally polycrystalline. Mor\
eover, Si spheres include many defects,)Tj
T*
(because the stress is generated by high-speed cooling. The correlation b\
etween the defect distributions and)Tj
T*
(spherical Si solar cell characteristics are evaluated by electron beam i\
nduced current \(EBIC\). By EBIC, we)Tj
T*
(confirmed that a part of strong electrically active defects in the grain\
is the main factor of characteristics)Tj
T*
(decrease, the strong electrically active defects on pn junction is the c\
ause of leakage current, and the entire)Tj
T*
(grain also has the weak electrically active defects. Moreover, the corre\
lation between defect types and)Tj
T*
(electrically active defects was directly identified by transmission elec\
tron microscope \(TEM\) after sampling a)Tj
T*
(part of the electrically active defect by focused ion beam \(FIB\). As a\
result, dislocations and the grain with)Tj
T*
(microcrystalline Si were observed. These crystal defects are determined \
to the main factor of spherical Si)Tj
T*
(solar cell characteristics decrease.)Tj
1 -2.5 Td
(It is necessary to inactivate and remove crystal defects in Si spheres f\
or the high-efficiency spherical Si)Tj
-1 -1.5 Td
(solar cells. At first, to inactivate electrically active defects, hydrog\
en passivation by RF plasma \(H-)Tj
T*
(passivation\) was done. Spherical Si solar cell characteristics were imp\
roved after H-passivation. By EBIC,)Tj
T*
(FIB, and TEM, H-passivation was found be effective in the grain with mic\
rocrystalline Si and grain)Tj
T*
(boundaries, but be not effective at dislocations. Moreover, it is necess\
ary to decrease the crystal defects for)Tj
T*
(high-efficiency spherical Si solar cells. Therefore, to decrease the coo\
ling rate of the Si sphere by decreasing)Tj
T*
(the convection heat transfer to ambient, Si spheres are dropped in a fre\
e-fall tower at a low pressure state. In)Tj
T*
(the low pressure spherical Si solar cell, dislocations and grains with m\
icrocrystalline Si which are observed in)Tj
T*
(conventional spherical Si solar cells disappeared. As a result, we achie\
ved the conversion efficiency of 11.1%)Tj
T*
(under 100 mW/cm2 AM 1.5 illumination at 25oC. However, dislocations were\
still confirmed at the vicinity)Tj
T*
(of the grain boundary in the low pressure Si sphere. The crystal growth \
of the Si sphere produced by the)Tj
T*
(dropping method occurred in arbitrary directions, and the stress could n\
ot be relaxed completely in the)Tj
T*
(vicinity of the grain boundary. To achieve the further high-efficiency s\
pherical Si solar cell, it is necessary to)Tj
T*
(control the crystal growth direction of the Si sphere.)Tj
ET
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