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High efficiency silicon solar cell based on asymmetric nanowire.

Ko MD, Rim T, Kim K, Meyyappan M, Baek CK - Sci Rep (2015)

Bottom Line: A maximum short circuit current density of 27.5 mA/cm(2) and an efficiency of 7.53% were realized without anti-reflection coating.Changing the silicon nanowire (SiNW) structure from conventional symmetric to asymmetric nature improves the efficiency due to increased short circuit current density.The proposed asymmetric structure has great potential to effectively improve the efficiency of the SiNW solar cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering, Pohang University of Science and Technology (POSTECH),77 Cheongam-Ro, Nam-Gu, Pohang, Kyeongbuk, Korea.

ABSTRACT
Improving the efficiency of solar cells through novel materials and devices is critical to realize the full potential of solar energy to meet the growing worldwide energy demands. We present here a highly efficient radial p-n junction silicon solar cell using an asymmetric nanowire structure with a shorter bottom core diameter than at the top. A maximum short circuit current density of 27.5 mA/cm(2) and an efficiency of 7.53% were realized without anti-reflection coating. Changing the silicon nanowire (SiNW) structure from conventional symmetric to asymmetric nature improves the efficiency due to increased short circuit current density. From numerical simulation and measurement of the optical characteristics, the total reflection on the sidewalls is seen to increase the light trapping path and charge carrier generation in the radial junction of the asymmetric SiNW, yielding high external quantum efficiency and short circuit current density. The proposed asymmetric structure has great potential to effectively improve the efficiency of the SiNW solar cells.

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Total reflection effect and optical characteristics of the asymmetric SiNW solar cells.(a) Schematic diagram of the total reflection at the sidewall and light concentration in the bottom center of the asymmetric SiNW. (b) Light reflection of the planar (black), symmetric SiNW solar cell with DT of 370 nm (red), and asymmetric SiNW solar cells with DB of 350 nm (blue) and 320 nm (green). (c) Comparison of the field intensity maps (E2) calculated by the FDTD model with a wavelength of 750 nm of the asymmetric SiNW (left, DT = 370 nm, DB = 320 nm) and symmetric SiNW (right, DT = DB = 370 nm). (d) Simulated optical carrier generation rate in the asymmetric and symmetric SiNWs. (e) EQE measurements of the symmetric SiNW solar cell with DT of 370 nm (red), and asymmetric SiNW solar cells with DB of 350 nm (blue), 320 nm (green), and 290 nm (pink).
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f2: Total reflection effect and optical characteristics of the asymmetric SiNW solar cells.(a) Schematic diagram of the total reflection at the sidewall and light concentration in the bottom center of the asymmetric SiNW. (b) Light reflection of the planar (black), symmetric SiNW solar cell with DT of 370 nm (red), and asymmetric SiNW solar cells with DB of 350 nm (blue) and 320 nm (green). (c) Comparison of the field intensity maps (E2) calculated by the FDTD model with a wavelength of 750 nm of the asymmetric SiNW (left, DT = 370 nm, DB = 320 nm) and symmetric SiNW (right, DT = DB = 370 nm). (d) Simulated optical carrier generation rate in the asymmetric and symmetric SiNWs. (e) EQE measurements of the symmetric SiNW solar cell with DT of 370 nm (red), and asymmetric SiNW solar cells with DB of 350 nm (blue), 320 nm (green), and 290 nm (pink).

Mentions: The asymmetric structure exhibits different light trapping characteristics compared with the conventional symmetric structure as shown in Fig. 2a. When the incident light proceeds from silicon to air, the refraction angle is much higher than the incident angle due to the difference between the refractive indices of silicon (3.6 ~ 7) and air (1), and light can be totally reflected at the sidewall of the SiNW. Hence, the incident light is continuously reflected in the nanowire until the incident angle becomes lower than a critical angle19. Because the angle of re-incidence of the reflected light (green) is lower than the angle of the first incident light (blue), the light trapping path is increased whenever the light is totally reflected at the outer shell of the asymmetric SiNW.


High efficiency silicon solar cell based on asymmetric nanowire.

Ko MD, Rim T, Kim K, Meyyappan M, Baek CK - Sci Rep (2015)

Total reflection effect and optical characteristics of the asymmetric SiNW solar cells.(a) Schematic diagram of the total reflection at the sidewall and light concentration in the bottom center of the asymmetric SiNW. (b) Light reflection of the planar (black), symmetric SiNW solar cell with DT of 370 nm (red), and asymmetric SiNW solar cells with DB of 350 nm (blue) and 320 nm (green). (c) Comparison of the field intensity maps (E2) calculated by the FDTD model with a wavelength of 750 nm of the asymmetric SiNW (left, DT = 370 nm, DB = 320 nm) and symmetric SiNW (right, DT = DB = 370 nm). (d) Simulated optical carrier generation rate in the asymmetric and symmetric SiNWs. (e) EQE measurements of the symmetric SiNW solar cell with DT of 370 nm (red), and asymmetric SiNW solar cells with DB of 350 nm (blue), 320 nm (green), and 290 nm (pink).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4495391&req=5

f2: Total reflection effect and optical characteristics of the asymmetric SiNW solar cells.(a) Schematic diagram of the total reflection at the sidewall and light concentration in the bottom center of the asymmetric SiNW. (b) Light reflection of the planar (black), symmetric SiNW solar cell with DT of 370 nm (red), and asymmetric SiNW solar cells with DB of 350 nm (blue) and 320 nm (green). (c) Comparison of the field intensity maps (E2) calculated by the FDTD model with a wavelength of 750 nm of the asymmetric SiNW (left, DT = 370 nm, DB = 320 nm) and symmetric SiNW (right, DT = DB = 370 nm). (d) Simulated optical carrier generation rate in the asymmetric and symmetric SiNWs. (e) EQE measurements of the symmetric SiNW solar cell with DT of 370 nm (red), and asymmetric SiNW solar cells with DB of 350 nm (blue), 320 nm (green), and 290 nm (pink).
Mentions: The asymmetric structure exhibits different light trapping characteristics compared with the conventional symmetric structure as shown in Fig. 2a. When the incident light proceeds from silicon to air, the refraction angle is much higher than the incident angle due to the difference between the refractive indices of silicon (3.6 ~ 7) and air (1), and light can be totally reflected at the sidewall of the SiNW. Hence, the incident light is continuously reflected in the nanowire until the incident angle becomes lower than a critical angle19. Because the angle of re-incidence of the reflected light (green) is lower than the angle of the first incident light (blue), the light trapping path is increased whenever the light is totally reflected at the outer shell of the asymmetric SiNW.

Bottom Line: A maximum short circuit current density of 27.5 mA/cm(2) and an efficiency of 7.53% were realized without anti-reflection coating.Changing the silicon nanowire (SiNW) structure from conventional symmetric to asymmetric nature improves the efficiency due to increased short circuit current density.The proposed asymmetric structure has great potential to effectively improve the efficiency of the SiNW solar cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering, Pohang University of Science and Technology (POSTECH),77 Cheongam-Ro, Nam-Gu, Pohang, Kyeongbuk, Korea.

ABSTRACT
Improving the efficiency of solar cells through novel materials and devices is critical to realize the full potential of solar energy to meet the growing worldwide energy demands. We present here a highly efficient radial p-n junction silicon solar cell using an asymmetric nanowire structure with a shorter bottom core diameter than at the top. A maximum short circuit current density of 27.5 mA/cm(2) and an efficiency of 7.53% were realized without anti-reflection coating. Changing the silicon nanowire (SiNW) structure from conventional symmetric to asymmetric nature improves the efficiency due to increased short circuit current density. From numerical simulation and measurement of the optical characteristics, the total reflection on the sidewalls is seen to increase the light trapping path and charge carrier generation in the radial junction of the asymmetric SiNW, yielding high external quantum efficiency and short circuit current density. The proposed asymmetric structure has great potential to effectively improve the efficiency of the SiNW solar cells.

No MeSH data available.


Related in: MedlinePlus