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Fabrication of Si heterojunction solar cells using P-doped Si nanocrystals embedded in SiNx films as emitters.

Wu PJ, Wang YC, Chen IC - Nanoscale Res Lett (2013)

Bottom Line: Increasing the nitrogen content enhances the optical gap E04 while deteriorating the electrical conductivity of the Si-NCs/SiNx film, leading to an increased short-circuit current density and a decreased fill factor of the heterojunction device.These trends could be interpreted by a bi-phase model which describes the Si-NCs/SiNx film as a mixture of a high-transparency SiNx phase and a low-resistivity Si-NC phase.A preliminary efficiency of 8.6% is achieved for the Si-NCs/sc-Si heterojunction solar cell.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Materials Science and Engineering, National Central University, Jhongli 320, Taiwan. ichen@ncu.edu.tw.

ABSTRACT
Si heterojunction solar cells were fabricated on p-type single-crystal Si (sc-Si) substrates using phosphorus-doped Si nanocrystals (Si-NCs) embedded in SiNx (Si-NCs/SiNx) films as emitters. The Si-NCs were formed by post-annealing of silicon-rich silicon nitride films deposited by electron cyclotron resonance chemical vapor deposition. We investigate the influence of the N/Si ratio in the Si-NCs/SiNx films on their electrical and optical properties, as well as the photovoltaic properties of the fabricated heterojunction devices. Increasing the nitrogen content enhances the optical gap E04 while deteriorating the electrical conductivity of the Si-NCs/SiNx film, leading to an increased short-circuit current density and a decreased fill factor of the heterojunction device. These trends could be interpreted by a bi-phase model which describes the Si-NCs/SiNx film as a mixture of a high-transparency SiNx phase and a low-resistivity Si-NC phase. A preliminary efficiency of 8.6% is achieved for the Si-NCs/sc-Si heterojunction solar cell.

No MeSH data available.


Optical and electrical properties of P-doped Si-NCs/SiNxfilms. (a) Absorption coefficients of the P-doped Si-NCs/SiNx films versus the incident photon energy. (b) Optical gap E04 and electrical conductivity of P-doped Si-NCs/SiNx films as a function of the Rc value.
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Figure 4: Optical and electrical properties of P-doped Si-NCs/SiNxfilms. (a) Absorption coefficients of the P-doped Si-NCs/SiNx films versus the incident photon energy. (b) Optical gap E04 and electrical conductivity of P-doped Si-NCs/SiNx films as a function of the Rc value.

Mentions: In this work, the optical absorption of the P-doped Si-NCs/SiNx film was evaluated using optical gap E04 defined as the energy at which the absorption coefficient is equal to 104 cm−1. In order to obtain the energy E04, the extinction coefficient was deduced from ellipsometry measurements, and then the absorption coefficient α was calculated from the determined extinction coefficient k through the relation α = 4πk / λ, where λ is the wavelength. Figure 4a shows absorption coefficients of the P-doped Si-NCs/SiNx films versus the incident photon energy. In addition, the electrical conductivity of the P-doped Si-NCs/SiNx film was measured by the van der Pauw method at room temperature. The derived optical gap E04 and electrical conductivity are shown as a function of the N2/SiH4 flow ratio in Figure 4b. As the nitrogen content increases, the electrical conductivity decreases from 46.4 to 6.7 S/cm over the investigated range of N2/SiH4 ratio, while the opposite trend is observed for the optical gap E04, increasing with a gain of 0.52 eV. The Si-NCs/SiNx film is considered as a two-phase heterogeneous material, consisting of low-resistivity Si-NCs needed for good carrier transport and the wide bandgap SiNx matrix for high transparency. According to the effective medium approximation [19], the Si-NCs/SiNx film can be schematized as an effective medium, and its physical properties (electrical conductivity and absorption coefficient) could be derived from the physical properties and volume fractions of each phase. Thus, the less conductive and more transparent material obtained with increasing nitrogen content could be ascribed to the reduction in volume fraction of Si-NCs, as depicted in Figure 2a. In addition, due to the quantum confinement effects [20], the shrinkage of the Si-NC size with increasing Rc value may result in bandgap expansion, which also leads to an increase in the effective optical gap of the Si-NCs/SiNx film.


Fabrication of Si heterojunction solar cells using P-doped Si nanocrystals embedded in SiNx films as emitters.

Wu PJ, Wang YC, Chen IC - Nanoscale Res Lett (2013)

Optical and electrical properties of P-doped Si-NCs/SiNxfilms. (a) Absorption coefficients of the P-doped Si-NCs/SiNx films versus the incident photon energy. (b) Optical gap E04 and electrical conductivity of P-doped Si-NCs/SiNx films as a function of the Rc value.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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Figure 4: Optical and electrical properties of P-doped Si-NCs/SiNxfilms. (a) Absorption coefficients of the P-doped Si-NCs/SiNx films versus the incident photon energy. (b) Optical gap E04 and electrical conductivity of P-doped Si-NCs/SiNx films as a function of the Rc value.
Mentions: In this work, the optical absorption of the P-doped Si-NCs/SiNx film was evaluated using optical gap E04 defined as the energy at which the absorption coefficient is equal to 104 cm−1. In order to obtain the energy E04, the extinction coefficient was deduced from ellipsometry measurements, and then the absorption coefficient α was calculated from the determined extinction coefficient k through the relation α = 4πk / λ, where λ is the wavelength. Figure 4a shows absorption coefficients of the P-doped Si-NCs/SiNx films versus the incident photon energy. In addition, the electrical conductivity of the P-doped Si-NCs/SiNx film was measured by the van der Pauw method at room temperature. The derived optical gap E04 and electrical conductivity are shown as a function of the N2/SiH4 flow ratio in Figure 4b. As the nitrogen content increases, the electrical conductivity decreases from 46.4 to 6.7 S/cm over the investigated range of N2/SiH4 ratio, while the opposite trend is observed for the optical gap E04, increasing with a gain of 0.52 eV. The Si-NCs/SiNx film is considered as a two-phase heterogeneous material, consisting of low-resistivity Si-NCs needed for good carrier transport and the wide bandgap SiNx matrix for high transparency. According to the effective medium approximation [19], the Si-NCs/SiNx film can be schematized as an effective medium, and its physical properties (electrical conductivity and absorption coefficient) could be derived from the physical properties and volume fractions of each phase. Thus, the less conductive and more transparent material obtained with increasing nitrogen content could be ascribed to the reduction in volume fraction of Si-NCs, as depicted in Figure 2a. In addition, due to the quantum confinement effects [20], the shrinkage of the Si-NC size with increasing Rc value may result in bandgap expansion, which also leads to an increase in the effective optical gap of the Si-NCs/SiNx film.

Bottom Line: Increasing the nitrogen content enhances the optical gap E04 while deteriorating the electrical conductivity of the Si-NCs/SiNx film, leading to an increased short-circuit current density and a decreased fill factor of the heterojunction device.These trends could be interpreted by a bi-phase model which describes the Si-NCs/SiNx film as a mixture of a high-transparency SiNx phase and a low-resistivity Si-NC phase.A preliminary efficiency of 8.6% is achieved for the Si-NCs/sc-Si heterojunction solar cell.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Materials Science and Engineering, National Central University, Jhongli 320, Taiwan. ichen@ncu.edu.tw.

ABSTRACT
Si heterojunction solar cells were fabricated on p-type single-crystal Si (sc-Si) substrates using phosphorus-doped Si nanocrystals (Si-NCs) embedded in SiNx (Si-NCs/SiNx) films as emitters. The Si-NCs were formed by post-annealing of silicon-rich silicon nitride films deposited by electron cyclotron resonance chemical vapor deposition. We investigate the influence of the N/Si ratio in the Si-NCs/SiNx films on their electrical and optical properties, as well as the photovoltaic properties of the fabricated heterojunction devices. Increasing the nitrogen content enhances the optical gap E04 while deteriorating the electrical conductivity of the Si-NCs/SiNx film, leading to an increased short-circuit current density and a decreased fill factor of the heterojunction device. These trends could be interpreted by a bi-phase model which describes the Si-NCs/SiNx film as a mixture of a high-transparency SiNx phase and a low-resistivity Si-NC phase. A preliminary efficiency of 8.6% is achieved for the Si-NCs/sc-Si heterojunction solar cell.

No MeSH data available.