Spherical silicon solar cells fabricated by high speed dropping method

Minemoto, Takashi; Akashi, Yoshito; Okamoto, Chikao; Omae, Satoshi; Yamaguchi, Yukio; Murozono, Mikio; Takakura, Hideyuki; Hamakawa, Yoshihiro

doi:10.1109/pvsc.2005.1488292

Cited by 4 publications

(5 citation statements)

References 2 publications

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“…1) Therefore, several groups have intensely investigated the growth of spherical Si crystals using the drop tube method in which the Si melt was ejected through an orifice of $1 mm and droplets solidified into spheres during free fall. [2][3][4] They, however, suffered from the severe polycrystallinity of spherical samples in which grain boundaries act as carrier recombination sites. This is strongly ascribed to the fact that the droplet experienced large undercooling prior to nucleation owing to the elimination of the crucible wall, one of the main heterogeneous nucleation sites.…”

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confidence: 99%

Spherical Silicon Crystal Formed by Semisolid Process in Drop Tube

Nagashio

Okamoto

Ando

et al. 2006

jjap

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Thus far, spherical Si crystals with $1 mm for solar cells have been grown by ejecting the melt above the melting point in a drop tube. The large undercooling prior to nucleation, however, results in severe polycrystallinity, which retrogrades the energy conversion efficiency. In the present study, we applied the semisolid process to the crystallization of Si droplets, where the melt was ejected with small solid particles formed by iterative cooling and heating of the melt with magnetic stirring at the melting point. The small solid particles that act as a nucleus efficiently suppressed the melt to be undercooled, resulting in an increase in the percentage of the spheres with few grains from 9.6 to 30%.

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confidence: 99%

Spherical Silicon Crystal Formed by Semisolid Process in Drop Tube

Nagashio

Okamoto

Ando

et al. 2006

jjap

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“…Spherical Si solar cells have attracted much attention as a promising candidate of high efficiency and low cost solar cells. [1][2][3][4] We proposed a new type of a spherical Si solar cell with a reflector cup, which consists of a concentrator of the spherical reflector cup with diameters of 2 -3 mm and a photovoltaic part of the spherical Si solar cell with a diameter of 1 mm 5) as shown in Fig. 1.…”

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confidence: 99%

Optical Design of Spherical Silicon Solar Cells with Reflector Cup

Ikuta

Minemoto

Takakura

et al. 2006

jjap

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A short-circuit current density (Jsc) of a spherical Si solar cell with a reflector cup has been calculated as a function of light concentration ratio, defined as the aperture area of the reflector cup divided by the projection area of the spherical Si solar cell, and incidence angle using a three-dimensional ray-tracing simulation. The calculation results show that the Jsc values of 39.7, 38.4, and 38.1 mA/cm2 can be obtained with the light concentration ratios of 4, 6, and 8, respectively, indicating that a higher concentration ratio reduces the optical efficiency of the reflector. Also, these results indicate that Jsc approaching 40 mA/cm2 can be realized without surface texturing in the spherical Si solar cell. Even in a high light concentration ratio of 8, a relatively high Jsc exceeding 37 mA/cm2 can be obtained for the incidence angles of 0–10°, indicating that the amount of spherical Si can be reduced effectively by the reflector cup.

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“…The above discussion leads to a proposal of a simple semiconductor device generating a sufficient voltage for water electrolysis that is attachable with ubiquitous electrocatalysts. As one of the candidates for efficient and space-saving solar cells, spherical silicon has been reported, consisting of a solid-state p-n junction between the inside and the outside of the sphere 44 45 46 . They are usually synthesized by a dropping method from inexpensive and low quality materials, which make it possible to reduce the cost in the cutting or polishing process of silicon ingots 44 45 and raw silicon materials itself.…”

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confidence: 99%

“…As one of the candidates for efficient and space-saving solar cells, spherical silicon has been reported, consisting of a solid-state p-n junction between the inside and the outside of the sphere 44 45 46 . They are usually synthesized by a dropping method from inexpensive and low quality materials, which make it possible to reduce the cost in the cutting or polishing process of silicon ingots 44 45 and raw silicon materials itself. Because the spherical silicon generates photocurrents up to approximately 1 mA and approximately 0.6 V of V OC with a relatively small volume 45 46 , the required voltage for the electrode reaction is easily adjusted by connecting them in series, e.g., a connection of 3–4 series for water splitting, without requirement of too large occupation area.…”

mentioning

confidence: 99%

“…They are usually synthesized by a dropping method from inexpensive and low quality materials, which make it possible to reduce the cost in the cutting or polishing process of silicon ingots 44 45 and raw silicon materials itself. Because the spherical silicon generates photocurrents up to approximately 1 mA and approximately 0.6 V of V OC with a relatively small volume 45 46 , the required voltage for the electrode reaction is easily adjusted by connecting them in series, e.g., a connection of 3–4 series for water splitting, without requirement of too large occupation area. Additionally, the spherical PVs can collect a much larger number of photons than flat plate solar cells because it can receive light from all directions.…”

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confidence: 99%

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A miniature solar device for overall water splitting consisting of series-connected spherical silicon solar cells

Kageshima

Kuwata²,

Nakata³

et al. 2016

Sci Rep

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A novel “photovoltaics (PV) + electrolyzer” concept is presented using a simple, small, and completely stand-alone non-biased device for solar-driven overall water splitting. Three or four spherical-shaped p-n junction silicon balls were successfully connected in series, named “SPHELAR.” SPHELAR possessed small projected areas of 0.20 (3PVs) and 0.26 cm2 (4PVs) and exhibited working voltages sufficient for water electrolysis. Impacts of the configuration on the PV module performance were carefully analyzed, revealing that a drastic increase in the photocurrent (≈20%) was attained by the effective utilization of a reflective sheet. Separate investigations on the electrocatalyst performance showed that non-noble metal based materials with reasonably small sizes (<0.80 cm2) exhibited substantial currents at the PV working voltage. By combining the observations of the PV characteristics, light management and electrocatalyst performance, solar-driven overall water splitting was readily achieved, reaching solar-to-hydrogen efficiencies of 7.4% (3PVs) and 6.4% (4PVs).

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Spherical silicon solar cells fabricated by high speed dropping method

Cited by 4 publications

References 2 publications

Spherical Silicon Crystal Formed by Semisolid Process in Drop Tube

Spherical Silicon Crystal Formed by Semisolid Process in Drop Tube

Optical Design of Spherical Silicon Solar Cells with Reflector Cup

A miniature solar device for overall water splitting consisting of series-connected spherical silicon solar cells

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