PROGRESS IN THE SURFACE PASSIVATION OF SILICON SOLAR CELLS (original) (raw)

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.

Thermal stability of the Al2O3 passivation on p-type silicon surfaces for solar cell application

physica status solidi (RRL) - Rapid Research Letters

Al2O3 has been shown to provide an outstanding passivation quality on p-type surfaces after annealing at moderate temperatures (~425 °C). However, most industrial silicon solar cells are based on printing technologies for metallization, including a high temperature firing step for the contact formation. To investigate the thermal stability of the Al2O3 passivation, symmetrical p and p+ np+ lifetime samples were coated with Al2O3 and exposed to typical firing processes at temperatures between 700 °C and 850 °C. Up to a firing temperature of 825 °C the Al2O3 passivation is shown to be stable on highly boron-doped surfaces. An emitter saturation current density of ~60 fA/cm2 could be measured for the p+ np+ samples, allowing a maximum open circuit voltage (Voc) >695 mV. The firing stability of the Al2O3 is an important step for the realization of an industrial n-type silicon solar cell.

Surface passivation of silicon solar cells using industrially relevant Al2O3 deposition techniques

Angewandte Chemie, 2010

The next generation of industrial silicon solar cells aims at efficiencies of 20% and above. To achieve this goal using ever-thinner silicon wafers, a highly effective surface passivation of the cell front and rear is required. In the past, finding a suitable dielectric layer providing a high-quality rear passivation has been a major challenge. Aluminium oxide (Al2O3) grown by atomic layer deposition (ALD) has only recently turned out to be a nearly perfect candidate for such a dielectric. However, conventional ALD is limited to deposition rates well below 2nm/min, which is incompatible with industrial solar cell production. This paper assesses the passivation quality provided by three different industrially relevant techniques for the deposition of Al2O3 layers, namely high-rate spatial ALD, plasma-enhanced chemical vapour deposition (PECVD) and reactive sputtering.

Al2O3 Passivation on c-si Surfaces for Low Temperature Solar Cell Applications

Energy Procedia, 2013

Functional passivation of high resistivity p-type c-Si wafer surfaces was achieved using 10 nm Al 2 O 3 layers and low temperatures for both the thermal ALD process and post-deposition anneal. Effective lifetime values higher than 1 ms were measured at excess carrier density n=10 15 cm-3. This result was reached in combination with temperatures of 100 °C and 200 °C for the Al 2 O 3 layer deposition and anneal, respectively. The Al 2 O 3 /c-Si interface was characterized using conductance-voltage and capacitance-voltage measurements. In particular, significantly reduced interface density of the electrically active defects D it ~ 2 x 10 10 eV-1 cm-2 was detected, which enabled excellent chemical passivation. The measured density of fixed charges at the interface, Q f , after anneal were in the range +1 x 10 12 to-1 x 10 12 cm-2 indicating that both inversion and accumulation conditions result in relevant field-effect passivation using Al 2 O 3 layers and low temperature processes. Numerical simulations on representative test structures show that the uniform Q f effect can be understood in terms of a surface damage region (SDR) present near the interface in combination with asymmetry in the lifetime of holes and electrons in the SDR. The combination of low processing temperatures, thin layers and good passivation properties facilitate a technology for future low temperature solar cell applications.

High efficiency n-type Si solar cells on Al2O3-passivated boron emitters

Applied Physics Letters, 2008

In order to utilize the full potential of solar cells fabricated on n-type silicon, it is necessary to achieve an excellent passivation on B-doped emitters. Experimental studies on test structures and theoretical considerations have shown that a negatively charged dielectric layer would be ideally suited for this purpose. Thus, in this work the negative-charge dielectric Al2O3 was applied as surface passivation layer on high-efficiency n-type silicon solar cells. With this front surface passivation layer, a confirmed conversion efficiency of 23.2% was achieved. For the open-circuit voltage Voc of 703.6mV, the upper limit for the emitter saturation current density J0e, including the metalized area, has been evaluated to be 29fA∕cm2. This clearly shows that an excellent passivation of highly doped p-type c-Si can be obtained at the device level by applying Al2O3.

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.

Advances in the Surface Passivation of Silicon Solar Cells

Energy Procedia, 2012

The surface passivation properties of aluminium oxide (Al 2 O 3) on crystalline Si are compared with the traditional passivation system of silicon nitride (SiN x). It is shown that Al 2 O 3 has fundamental advantages over SiN x when applied to the rear of p-type silicon solar cells as well as to the p + emitter of n-type silicon solar cells. Special emphasis is paid to the transfer of Al 2 O 3 into industrial solar cell production. We compare different Al 2 O 3 deposition techniques suitable for mass production such as ultrafast spatial atomic layer deposition, inline plasma-enhanced chemical vapour deposition and reactive sputtering. Finally, we review the most recent cell results with Al 2 O 3 passivation and give a brief outlook on the future prospects of Al 2 O 3 in silicon solar cell production.