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A novel method for crystalline silicon solar cells with low contact resistance and antireflection coating by an oxidized Mg layer.

Lee J, Lee YJ, Ju M, Ryu K, Kim B, Yi J - Nanoscale Res Lett (2012)

Bottom Line: In this paper, an evaporated Mg layer is used to reduce series resistance of c-Si solar cells.Small work function difference between Mg and n-type silicon reduces the contact resistance.It can be applied to the manufacturing of low-cost, simple, and high-efficiency solar cells.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Information and Communication Engineering, Sungkyunkwan University, Suwon, 440-746, South Korea. yi@yurim.skku.ac.kr.

ABSTRACT
One of the key issues in the solar industry is lowering dopant concentration of emitter for high-efficiency crystalline solar cells. However, it is well known that a low surface concentration of dopants results in poor contact formation between the front Ag electrode and the n-layer of Si. In this paper, an evaporated Mg layer is used to reduce series resistance of c-Si solar cells. A layer of Mg metal is deposited on a lightly doped n-type Si emitter by evaporation. Ag electrode is screen printed to collect the generated electrons. Small work function difference between Mg and n-type silicon reduces the contact resistance. During a co-firing process, Mg is oxidized, and the oxidized layer serves as an antireflection layer. The measurement of an Ag/Mg/n-Si solar cell shows that Voc, Jsc, FF, and efficiency are 602 mV, 36.9 mA/cm2, 80.1%, and 17.75%, respectively. It can be applied to the manufacturing of low-cost, simple, and high-efficiency solar cells.

No MeSH data available.


Sun-Voc data of the processed solar cells with different Mg thicknesses.
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Figure 6: Sun-Voc data of the processed solar cells with different Mg thicknesses.

Mentions: where λ0 is 550 nm (where the strongest intensity of sunlight is emitted), n1 is the refractive index of MgO (which is equal to 1.74), and d is the thickness of the ARC layer. Thicker MgO results in less reflectance as its thickness gets close to 79 nm which is reported to be an optimized thickness of MgO for the ARC layer of solar cells [13]. Figure 5 and Table 1 show the DIV measured. The current is measured in the potential range of 0 to 0.8 V. The current of the PN junction diode can be separated into two regions: the quasi-neutral region (n1) and the space-charge region (n2) recombination/generation [14]. In the two-diode model, this deviation is taken into account by including a second diode. The second diode expresses generation and recombination currents within the space-charge region. When the ideality factor of the second diode deviates far from 2, leakage current increases, parallel resistance [Rsh] decreases, and series resistance [Rs] increases. Increased leakage current and decreased Rsh cause a decrease in the short-circuit current density [Jsc]. Increased Rs and decreased Rsh result in a sharp decline in the fill factor [FF]. In Table 1, it is shown that the leakage current gets higher as the thickness of the Mg metal increases. This is due to the fact that a thicker Mg metal digs more into the Si substrate and results in poor solar cell performance. The extracted optimized conditions of the Mg metal layer are applied to the c-Si solar cell, and its properties are measured. Figure 6 and Table 2 show the sun-open-circuit voltage [Voc] characteristics of solar cells with different Mg thicknesses. It is seen that the cell with Mg200 Å deposition has the best efficiency. The Voc of the cell is 602 mV, and the Jsc is 36.9 mA/cm2. Relatively low Voc value is obtained, and it is attributed to the reduced band bending caused by a low doping concentration of the emitter layer. However, the Jsc value is relatively high due to the effect of the high Rs emitter and the MgO layer collecting more carriers which would have usually been recombined at the front surface. Consequently, with this high Jsc value, the high-Rs c-Si solar cell reaches a conversion efficiency of 17.75%.


A novel method for crystalline silicon solar cells with low contact resistance and antireflection coating by an oxidized Mg layer.

Lee J, Lee YJ, Ju M, Ryu K, Kim B, Yi J - Nanoscale Res Lett (2012)

Sun-Voc data of the processed solar cells with different Mg thicknesses.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3275516&req=5

Figure 6: Sun-Voc data of the processed solar cells with different Mg thicknesses.
Mentions: where λ0 is 550 nm (where the strongest intensity of sunlight is emitted), n1 is the refractive index of MgO (which is equal to 1.74), and d is the thickness of the ARC layer. Thicker MgO results in less reflectance as its thickness gets close to 79 nm which is reported to be an optimized thickness of MgO for the ARC layer of solar cells [13]. Figure 5 and Table 1 show the DIV measured. The current is measured in the potential range of 0 to 0.8 V. The current of the PN junction diode can be separated into two regions: the quasi-neutral region (n1) and the space-charge region (n2) recombination/generation [14]. In the two-diode model, this deviation is taken into account by including a second diode. The second diode expresses generation and recombination currents within the space-charge region. When the ideality factor of the second diode deviates far from 2, leakage current increases, parallel resistance [Rsh] decreases, and series resistance [Rs] increases. Increased leakage current and decreased Rsh cause a decrease in the short-circuit current density [Jsc]. Increased Rs and decreased Rsh result in a sharp decline in the fill factor [FF]. In Table 1, it is shown that the leakage current gets higher as the thickness of the Mg metal increases. This is due to the fact that a thicker Mg metal digs more into the Si substrate and results in poor solar cell performance. The extracted optimized conditions of the Mg metal layer are applied to the c-Si solar cell, and its properties are measured. Figure 6 and Table 2 show the sun-open-circuit voltage [Voc] characteristics of solar cells with different Mg thicknesses. It is seen that the cell with Mg200 Å deposition has the best efficiency. The Voc of the cell is 602 mV, and the Jsc is 36.9 mA/cm2. Relatively low Voc value is obtained, and it is attributed to the reduced band bending caused by a low doping concentration of the emitter layer. However, the Jsc value is relatively high due to the effect of the high Rs emitter and the MgO layer collecting more carriers which would have usually been recombined at the front surface. Consequently, with this high Jsc value, the high-Rs c-Si solar cell reaches a conversion efficiency of 17.75%.

Bottom Line: In this paper, an evaporated Mg layer is used to reduce series resistance of c-Si solar cells.Small work function difference between Mg and n-type silicon reduces the contact resistance.It can be applied to the manufacturing of low-cost, simple, and high-efficiency solar cells.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Information and Communication Engineering, Sungkyunkwan University, Suwon, 440-746, South Korea. yi@yurim.skku.ac.kr.

ABSTRACT
One of the key issues in the solar industry is lowering dopant concentration of emitter for high-efficiency crystalline solar cells. However, it is well known that a low surface concentration of dopants results in poor contact formation between the front Ag electrode and the n-layer of Si. In this paper, an evaporated Mg layer is used to reduce series resistance of c-Si solar cells. A layer of Mg metal is deposited on a lightly doped n-type Si emitter by evaporation. Ag electrode is screen printed to collect the generated electrons. Small work function difference between Mg and n-type silicon reduces the contact resistance. During a co-firing process, Mg is oxidized, and the oxidized layer serves as an antireflection layer. The measurement of an Ag/Mg/n-Si solar cell shows that Voc, Jsc, FF, and efficiency are 602 mV, 36.9 mA/cm2, 80.1%, and 17.75%, respectively. It can be applied to the manufacturing of low-cost, simple, and high-efficiency solar cells.

No MeSH data available.