Crystalline Silicon PERC Solar Cell with Ozonized AlOx Passivation Layer on the Rear Side (original) (raw)
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Study on Annealing Process of Aluminum Oxide Passivation Layer for PERC Solar Cells
Coatings, 2021
In this study, Atomic Layer Deposition (ALD) equipment was used to deposit Al2O3 film on a p-type silicon wafer, trimethylaluminum (TMA) and H2O were used as precursor materials, and then the post-annealing process was conducted under atmospheric pressure. The Al2O3 films annealed at different temperatures between 200–500 °C were compared to ascertain the effect of passivation films and to confirm the changes in film structure and thickness before and after annealing through TEM images. Furthermore, the negative fixed charge and interface defect density were analyzed using the C-V measurement method. Photo-induced carrier generation was used to measure the effective minority carrier lifetime, the implied open-circuit voltage, and the effective surface recombination velocity of the film. The carrier lifetime was found to be the longest (2181.7 μs) for Al2O3/Si post-annealed at 400 °C. Finally, with the use of VHF (40.68 MHz) plasma-enhanced chemical vapor deposition (PECVD) equipment...
PERC SOLAR CELLS: COMPARISON OF AL PRECURSORS FOR REAR-SIDE SURFACE PASSIVATION
PERC cells were fabricated using two different aluminum precursors for the Al2O3 rear surface passivation layer. TMA and non-pyrophoric DMAi based Al2O3 layers were implemented in p-type Cz-Si PERC for rear surface passivation. The Al2O3 layers deposition was performed by ALD, PEALD and PECVD. The best conversion efficiency was obtained for the cells using a 10 nm DMAi based Al2O3 layer, deposited by PECVD (20.1 %). The TMA-Al2O3 based PERC cells achieved nearly identical conversion efficiencies (max 20.0 %).
Evaluation of Spatial ALD of Al2O3 for Rear Surface Passivation of mc-Si PERC Solar Cells
2016
In this work the evaluation results on industrial p-type mc-Si PERC cells using spatial atomic layer deposition for aluminum oxide from SoLayTec are shown. By optimizing the process flow and integrating a postdeposition anneal into the SiNx capping process we achieve 0.15% higher cell efficiency compared to remote microwave plasma-enhanced chemical vapor deposition. Furthermore, it is shown that the improved passivation quality resulting in Voc gain remains constant during light and elevated temperature induced degradation measurements.
Towards industrial n-type PERT silicon solar cells: rear passivation and metallization scheme
Energy Procedia, 2011
Recently, we presented an industrially feasible passivation and contacting scheme for the front side boron emitter of n-type silicon solar cells based on firing processes. On these cells, efficiencies up to 20.8% have been achieved on small areas. These cells feature a fully-metalized BSF on the rear side, which limits the V OC to about 655 mV. When changing to a PERT cell design with a passivated BSF, both the V OC as well as the J SC can be improved due to a reduced recombination at the rear and an improved optical confinement. In this work we studied different POCl 3 diffusions for their applicability to n-type PERT solar cells with respect to passivation and metallization. The achieved results have been used to fabricate a first batch of n-type PERT solar cells, on which V OC values up to 671 mV have been measured. The improved internal quantum efficiency above 900 nm confirms the improvement of the rear side of the cell. The boron emitter of this cell was passivated with a stack of 5 Å ALD Al 2 O 3 (four ALD cycles) and 70 nm PECVD SiN x . Thus the V OC of 671 mV demonstrates furthermore, that the Al 2 O 3 thickness of fired Al 2 O 3 /SiN x stacks for the passivation of boron emitters can be drastically reduced to four atomic layers of Al 2 O 3 .
2008 33rd IEEE Photovolatic Specialists Conference, 2008
We present independently confirmed efficiencies above 20% for PERC-type solar cells with the pointcontacted rear being either passivated by atomic-layerdeposited Al2O3 or by stacks consisting of an ultrathin Al2O3 film and a thicker PECVD-SiOx layer. Internal quantum efficiency measurements reveal that the effective rear surface recombination velocities of the single-layer Al2O3passivated cells are comparable to those measured on reference cells passivated by an aluminum-annealed thermal SiO2, while those of the Al2O3/SiOx-passivated cells are even lower. Very low effective rear surface recombination velocities of only 70 cm/s are reported for the Al2O3/SiOx stacks, including metalized areas on the cell rear.
Integration of Spatial ALD Aluminum Oxide for Rear Side Passivation of p-Type PERC/PERL Solar Cells
In this paper we present an overview of the integration of amorphous aluminum oxide (Al 2 O 3 ) as rear side passivation layer for large area industrial PERC solar cells (i-PERC). The technique used for the deposition of the Al 2 O 3 layers is spatial Atomic Layer Deposition (ALD), for its industrial relevance due to the high deposition speed and low Trimethyl-Aluminum (TMA) consumption. After analyzing the surface passivation properties, we will describe how Al 2 O 3 can be integrated in an i-PERC process flow in a simple and cost-effective way, while maintaining high levels of solar cell efficiency. In particular, a special effort is devoted in finding solutions for process simplification and in the reduction of the cost per wafer (€/W) of the spatial ALD process step. Top efficiencies of 20.1 % and 20.6 % have been reached (Cz-Si, 6 inch cells) when coupling a spatial ALD Al 2 O 3 rear passivation to a standard i-PERC integration flow with front Ag-screen printed or Ni/Cu/Ag plated contacts, respectively. Besides passivation, ALD Al 2 O 3 can also be used as doping source of aluminum to form localized p + back surface field (BSF) regions at the rear contact by means of laser processing. In this way, dielectric opening and BSF are formed simultaneously and firing step is not needed anymore, leading both to a suppression of Al 2 O 3 blistering and optical enhancement. This process is a suitable complement of front contact formation based on plating schemes. Ni/Cu/Ag-plated solar cells with rear laser doping from ALD Al 2 O 3 layers have been fabricated with efficiencies topping 20.4 % (FF = 79.7 %) and outperforming the control group featuring local BSF formed via a firing step.
Surface passivation of high-efficiency silicon solar cells by atomic-layer-deposited Al 2 O 3
Progress in Photovoltaics: Research and Applications, 2008
Atomic-layer-deposited aluminium oxide (Al 2 O 3 ) is applied as rear-surface-passivating dielectric layer to passivated emitter and rear cell (PERC)-type crystalline silicon (c-Si) solar cells. The excellent passivation of low-resistivity p-type silicon by the negative-charge-dielectric Al 2 O 3 is confirmed on the device level by an independently confirmed energy conversion efficiency of 20Á6%. The best results are obtained for a stack consisting of a 30 nm Al 2 O 3 film covered by a 200 nm plasma-enhanced-chemical-vapour-deposited silicon oxide (SiO x ) layer, resulting in a rear surface recombination velocity (SRV) of 70 cm/s. Comparable results are obtained for a 130 nm single-layer of Al 2 O 3 , resulting in a rear SRV of 90 cm/s.
Applied Physics B, 2019
Effect of process parameters on Al 2 O 3 deposited using Atomic Layer Deposition (ALD) for the surface passivation of c-silicon surface has been investigated. Surface passivation properties of Al 2 O 3 have been measured by evaluating the minority carrier lifetime and interface charges at the Si∕Al 2 O 3 interface. It has been observed that surface passivation properties of Al 2 O 3 are strongly dependent on process parameters such as substrate temperature, annealing temperature, and thickness of the deposited Al 2 O 3 film. Minority carrier lifetime, effective charge density (Q eff), and interface defect density (D it) were observed to vary from 180 to 355 μs , − 2.3 × 10 12 to −1.46 × 10 13 cm −2 and 1.2 × 10 9 to 1.9 × 10 10 eV −1 cm −2 , respectively, for various process parameters. Al 2 O 3 film based on the optimized process parameters were then used as a passivation layer in fabricating industrial PERC solar cells. Effect of Al 2 O 3 passivation in PERC solar cells has been demonstrated by comparing the characteristics of the PERC solar cells with that of the standard Al BSF solar cells. An efficiency improvement of ∼ 0.8% has been observed in passivated emitter rear cells (PERC) solar cells as compared to the standard aluminum back surface field (Al BSF) solar cells.
Sputtered Aluminum Oxide for Rear Side Passivation of P-Type Silicon Solar Cells
Aluminum oxide is an excellent candidate for the surface passivation of silicon wafers. Due the incorporation of a high density of negative charges near the interface surface and a low defect density a very good passivation can be achieved. Today, aluminum oxide layers are predominantly deposited by atomic layer deposition and plasma-enhanced chemical vapor deposition. Reactive sputtering is an alternative not requiring trimethylaluminum. Nevertheless, there are doubts concerning the passivation quality of sputtered aluminum oxide. In this contribution we analyse the influence of deposition parameters on the properties of the sputtered layers. Measurements of interface defects density and the density of fixed charges at the interface can explain a good passivation quality after firing. Additionally, results for LFC-PERC solar cells are presented showing a statistically significant improve in efficiency compared to standard BSF solar cells. This can be explained by a lower recombination rate and a higher reflectivity at the rear side of the solar cell.