Light management techniques have become important in recent times in the endeavor of taking silicon thin-film photovoltaics to the next level. Such techniques aim to bring about a better utilization of the solar spectrum by the solar cell, mainly using two approaches: Enhancing the intensity of the light that enters and gets converted to electricity, and enhancing the spectral matching. Light-trapping methods are aimed at decreasing the reflective losses and increasing the path of the photon within the cell by scattering techniques. This is usually achieved by using a textured surface which creates both scattering effect and decrease in reflective loss. Techniques for decreasing spectral mismatch-induced losses include up-conversion methods that make possible the absorption of sub-band gap photons by converting them to higher energy photons, which are then directed back to the solar cell, absorbed and converted to electricity [1]. The focus of the present study is the optimization of the back side of the solar cell to enhance the light utilization in substrate configuration. The presented advancements in substrate configuration are targeted at future applications in flexible non-transparent substrates with the potential for up-scaling to roll to roll deposition techniques. We have used different textured substrates to grow amorphous silicon thin-film solar cells on them in substrate or n-i-p configuration. To further enhance the light trapping effect we have utilized a method of light up-conversion using Er3+ ions. Er3+ doped materials are known for their up-conversion luminescence, and Er3+ ions are particularly useful for converting infrared radiation into visible light due to a favorable electronic energy level structure. We have used ZnO as the host matrix for embedding the Er3+ ions particularly because ZnO has a low phonon energy leading to reduced multi-phonon relaxation between closely spaced energy levels. A constraint in the use of up-conversion in commercial solar cells is that higher intensities of light are required for achieving higher up-conversion quantum efficiencies. We have overcome this problem by applying an approach of plasmonic assisted up-conversion using encapsulating size distributed silver nanoparticles within an Er doped ZnO matrix. The nanoparticles have strong scattering properties due to localized surface plasmons [2,3] depending on their size, shape and position, the optimization of which is a separate study. The combined approach applied in our study demonstrates enhanced light trapping, increasing the quantum efficiency further [1]. Individual layers in the solar-cell structures are well characterized separately and we used optimized layers in the final device configuration [4]. In this report we present the studies on solar cells using different combinations of textured back reflector with up-conversion material layer. The combination of light trapping scheme along with up-conversion is an advanced concept that has the potential to be used in the commercial setting of solar cell manufacturing. With further optimization of the layers and the solar cell, the application of the presented light management scheme in thin film solar cells should lead to a higher stabilized efficiency.
Textured back reflector with plasmonic assisted up-conversion for efficient light trapping in solar cells
R Rizzoli
2012
Abstract
Light management techniques have become important in recent times in the endeavor of taking silicon thin-film photovoltaics to the next level. Such techniques aim to bring about a better utilization of the solar spectrum by the solar cell, mainly using two approaches: Enhancing the intensity of the light that enters and gets converted to electricity, and enhancing the spectral matching. Light-trapping methods are aimed at decreasing the reflective losses and increasing the path of the photon within the cell by scattering techniques. This is usually achieved by using a textured surface which creates both scattering effect and decrease in reflective loss. Techniques for decreasing spectral mismatch-induced losses include up-conversion methods that make possible the absorption of sub-band gap photons by converting them to higher energy photons, which are then directed back to the solar cell, absorbed and converted to electricity [1]. The focus of the present study is the optimization of the back side of the solar cell to enhance the light utilization in substrate configuration. The presented advancements in substrate configuration are targeted at future applications in flexible non-transparent substrates with the potential for up-scaling to roll to roll deposition techniques. We have used different textured substrates to grow amorphous silicon thin-film solar cells on them in substrate or n-i-p configuration. To further enhance the light trapping effect we have utilized a method of light up-conversion using Er3+ ions. Er3+ doped materials are known for their up-conversion luminescence, and Er3+ ions are particularly useful for converting infrared radiation into visible light due to a favorable electronic energy level structure. We have used ZnO as the host matrix for embedding the Er3+ ions particularly because ZnO has a low phonon energy leading to reduced multi-phonon relaxation between closely spaced energy levels. A constraint in the use of up-conversion in commercial solar cells is that higher intensities of light are required for achieving higher up-conversion quantum efficiencies. We have overcome this problem by applying an approach of plasmonic assisted up-conversion using encapsulating size distributed silver nanoparticles within an Er doped ZnO matrix. The nanoparticles have strong scattering properties due to localized surface plasmons [2,3] depending on their size, shape and position, the optimization of which is a separate study. The combined approach applied in our study demonstrates enhanced light trapping, increasing the quantum efficiency further [1]. Individual layers in the solar-cell structures are well characterized separately and we used optimized layers in the final device configuration [4]. In this report we present the studies on solar cells using different combinations of textured back reflector with up-conversion material layer. The combination of light trapping scheme along with up-conversion is an advanced concept that has the potential to be used in the commercial setting of solar cell manufacturing. With further optimization of the layers and the solar cell, the application of the presented light management scheme in thin film solar cells should lead to a higher stabilized efficiency.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
