Symmetrical Al2O3-based passivation layers for p- and n-type silicon
| Autor: | Ingo Dirnstorfer, Frank Benner, Daniel K. Simon, Paul M. Jordan, Claudia Richter, Thomas Mikolajick |
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| Rok vydání: | 2014 |
| Předmět: |
Recombination velocity
Materials science Passivation Renewable Energy Sustainability and the Environment N type silicon business.industry Field effect Carrier lifetime Surfaces Coatings and Films Electronic Optical and Magnetic Materials Stack (abstract data type) Optoelectronics Electrical measurements business Recombination |
| Zdroj: | Solar Energy Materials and Solar Cells. 131:72-76 |
| ISSN: | 0927-0248 |
| Popis: | Al 2 O 3 nanolayers, as currently used in the solar industry, provide excellent passivation over the entire injection level range for p -type Si. A high concentration of negative fixed charges guarantees excellent field effect passivation. However, on n -type Si, those fixed charges create an inversion layer at the surface, which opens an additional near-surface recombination channel. This results in a reduced minority carrier lifetime at low injection levels, which is the operation condition of solar cells. In this work, a passivation layer stack is presented, showing excellent performance within the complete injection level range symmetrically for both p - and n -type Si. This layer stack consists of 20 nm Al 2 O 3 combined with a thin HfO 2 or SiO 2 interface. Electrical measurements show a reduction of the fixed charge density to virtually ‘zero’, when the interface layer is adjusted accordingly. This affects the field effect passivation and leads to a decrease of the near surface recombination in n -type Si. The introduction of five cycles of atomic layer deposited HfO 2 improves the effective carrier lifetime in passivated n -type Si from 6 to 15 ms at an injection level of 5×10 12 cm − 3 . The same passivation stack hardly influences the lifetime in p -type Si. The effective surface recombination velocity reaches values below 1 cm/s for both types of substrate doping. In case of the introduction of a 1 nm thick SiO 2 interface, which also results in ‘zero’ fixed charges, the surface recombination velocity reaches a value of up to 200 cm/s due to enhanced surface recombination. The comparison of both passivation stacks shows that the introduction of an ultrathin HfO 2 interface is the most promising approach to achieve a symmetrical passivation layer for p - and n -type Si. |
| Databáze: | OpenAIRE |
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