Today, about 80% of silicon solar cells industrially manufactured worldwide apply screen printing for the deposition of the silver front and the full-area aluminium rear metal contacts. In production, conversion efficiencies of ~18–18.5% are demonstrated on monocrystalline silicon wafers. The ...
Today, about 80% of silicon solar cells industrially manufactured worldwide apply screen printing for the deposition of the silver front and the full-area aluminium rear metal contacts. In production, conversion efficiencies of ~18–18.5% are demonstrated on monocrystalline silicon wafers. The trend to thinner crystalline silicon wafers in the production of silicon solar cells instigates a re-evolution of the back surface field (BSF) formation. Aluminium layers, whose thickness is typically over 10 um, are commonly used for BSF formation. The screen-printed full-area aluminium back-surface field (Al-BSF) exhibits only a moderate passivation quality, with typical rearsurface recombination velocities (Seff, rear) ranging from 200 to 600cm/s. an aluminum layer is formed on the back surface of a p-type silicon wafer, typically by evaporation or sputtering or by printing of an aluminum paste. The contact is subsequently "formed" by an appropriate heat-treatment. Thicker layers of aluminum typically lead to improved cell performance, particularly with respect to open-circuit voltage and short-circuit current. The improvement has been variously ascribed to gettering or to the formation of a highlow junction at the back surface. Analysis and characterization of the BSF structures show that this formation process satisfies the two main requirements for achieving low Seff: 1) deep p+ regions and 2) uniform junctions. Screen-printing is ideally suited for fast deposition of thick Al films which, upon alloying, result in deep BSF regions. Use of a rapid alloying treatment is shown to significantly improve the BSF junction uniformity and reduce Seff. The Al-BSF’s formed by screen-printing and rapid alloying have been integrated into both laboratory and industrial-type fabrication sequences to achieve solar cell efficiencies. In the section 1~5 we considered the operation of a photovoltaic cell and the significant parameters that characterize its performance. The screen printed solar cell overview was discussed with following the process concept. This paper mainly discussed about electrical properties and formation mechanisms of aluminum back contact including BSF. In chapter 6, the back contacts for Si solar cells made by Al evaporation and screen printing Al paste were studied by TEM. Si was found to diffuse into the Al during heating. Si diffusion formed vacancies in the Si wafer and Al could then penetrate the Si wafer in spiked formations. The Al spikes retracted during cooling, leaving a doped back surface field region. In the chapter 7, N-type silicon with aluminum emitters for rear junctions was studied; aluminum back surface fields were replaced with n-type silicon wafers. Aluminum rear emitters for n-type silicon solar cells were studied with different rapid thermal processing condition. With fast ramping-up and fast cooling, the aluminum rear junction was formed uniformly with low emitter recombination current. The effects of junction quality on solar cells’ efficiency were investigated. The purpose of chapter 8 work is to investigate a back surface field (BSF) on variety wafer resistivity for industrial crystalline silicon solar cells. As pointed out in this manuscript, doping a crucible grown Cz Si ingot with Ga offers a sure way of eliminating the light induced degradation (LID) because the LID defect is composed of B and O complex. However, the low segregation coefficient of Ga in Si causes a much wider resistivity variation along the Ga doped Cz Si ingot. Because of the resistivity variation the Cz Si wafer from different locations has different performance as know. In the light of B doped wafer, we made wider resistivity in Si ingot; we investigated the how resistivities work on the solar cells performance as a BSF quality. In chapter 9, we discussed about relation of bump formation and BSF quality. In module processes, wafer-based solar cell can break through stress during soldering uneven rear aluminum surfaces - a serious problem that affects throughput. This work examined rear surfaces with respect to controllable process factors such as ramping and cooling rates during rapid thermal processing, and the fineness of aluminum powder used in the screen-printed paste. A faster ramp up rate resulted in a uniform temperature gradient between the aluminum and silicon surfaces. As a results, the bumps on the aluminum surface were small and of high density. Fine aluminum metal powder in the paste for screen-printing contact points resulted in large distribution, high-density bumps. Bumps formed during cooling in metallization, their sizes and densities were dependent the on uniformity of the aluminum and silicon liquid wetting of the silicon surface.
Today, about 80% of silicon solar cells industrially manufactured worldwide apply screen printing for the deposition of the silver front and the full-area aluminium rear metal contacts. In production, conversion efficiencies of ~18–18.5% are demonstrated on monocrystalline silicon wafers. The trend to thinner crystalline silicon wafers in the production of silicon solar cells instigates a re-evolution of the back surface field (BSF) formation. Aluminium layers, whose thickness is typically over 10 um, are commonly used for BSF formation. The screen-printed full-area aluminium back-surface field (Al-BSF) exhibits only a moderate passivation quality, with typical rearsurface recombination velocities (Seff, rear) ranging from 200 to 600cm/s. an aluminum layer is formed on the back surface of a p-type silicon wafer, typically by evaporation or sputtering or by printing of an aluminum paste. The contact is subsequently "formed" by an appropriate heat-treatment. Thicker layers of aluminum typically lead to improved cell performance, particularly with respect to open-circuit voltage and short-circuit current. The improvement has been variously ascribed to gettering or to the formation of a highlow junction at the back surface. Analysis and characterization of the BSF structures show that this formation process satisfies the two main requirements for achieving low Seff: 1) deep p+ regions and 2) uniform junctions. Screen-printing is ideally suited for fast deposition of thick Al films which, upon alloying, result in deep BSF regions. Use of a rapid alloying treatment is shown to significantly improve the BSF junction uniformity and reduce Seff. The Al-BSF’s formed by screen-printing and rapid alloying have been integrated into both laboratory and industrial-type fabrication sequences to achieve solar cell efficiencies. In the section 1~5 we considered the operation of a photovoltaic cell and the significant parameters that characterize its performance. The screen printed solar cell overview was discussed with following the process concept. This paper mainly discussed about electrical properties and formation mechanisms of aluminum back contact including BSF. In chapter 6, the back contacts for Si solar cells made by Al evaporation and screen printing Al paste were studied by TEM. Si was found to diffuse into the Al during heating. Si diffusion formed vacancies in the Si wafer and Al could then penetrate the Si wafer in spiked formations. The Al spikes retracted during cooling, leaving a doped back surface field region. In the chapter 7, N-type silicon with aluminum emitters for rear junctions was studied; aluminum back surface fields were replaced with n-type silicon wafers. Aluminum rear emitters for n-type silicon solar cells were studied with different rapid thermal processing condition. With fast ramping-up and fast cooling, the aluminum rear junction was formed uniformly with low emitter recombination current. The effects of junction quality on solar cells’ efficiency were investigated. The purpose of chapter 8 work is to investigate a back surface field (BSF) on variety wafer resistivity for industrial crystalline silicon solar cells. As pointed out in this manuscript, doping a crucible grown Cz Si ingot with Ga offers a sure way of eliminating the light induced degradation (LID) because the LID defect is composed of B and O complex. However, the low segregation coefficient of Ga in Si causes a much wider resistivity variation along the Ga doped Cz Si ingot. Because of the resistivity variation the Cz Si wafer from different locations has different performance as know. In the light of B doped wafer, we made wider resistivity in Si ingot; we investigated the how resistivities work on the solar cells performance as a BSF quality. In chapter 9, we discussed about relation of bump formation and BSF quality. In module processes, wafer-based solar cell can break through stress during soldering uneven rear aluminum surfaces - a serious problem that affects throughput. This work examined rear surfaces with respect to controllable process factors such as ramping and cooling rates during rapid thermal processing, and the fineness of aluminum powder used in the screen-printed paste. A faster ramp up rate resulted in a uniform temperature gradient between the aluminum and silicon surfaces. As a results, the bumps on the aluminum surface were small and of high density. Fine aluminum metal powder in the paste for screen-printing contact points resulted in large distribution, high-density bumps. Bumps formed during cooling in metallization, their sizes and densities were dependent the on uniformity of the aluminum and silicon liquid wetting of the silicon surface.
주제어
#metallization Photovoltaics Al back contact Silicon Solar cells
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