In addition to mixing tripassium aluminum and nitrous oxide, the positive coating in the battery workshop generates aluminum oxide through a plasma excitation reaction. Aluminum oxide film is used as a surface passivation material for solar cells. Because it contains high-density fixed negative charges, it is exceptional for passivating the P-type layer of solar cells and has become one of the main processes for high-efficiency cells. . The currently most common aluminum oxide coating systems can be divided into two categories: atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD). The ALD method uses trimethyl aluminum (TMA) and water vapor (H2O) for cross coverage. On the surface of the silicon wafer, aluminum oxide reacts at a certain temperature. The ALD system offers qualityhigh coating, but the coating speed is slow and difficult to mass produce. PECVD mixes trimethyl aluminum (TMA) and nitrous oxide in vacuum to generate aluminum oxide through a plasma excitation reaction. The coating quality of this PECVD system is moderate, but the coating speed is fast and it is easy to achieve mass production. In particular, the chain PECVD method is easier to mass produce.
Double-sided contact silicon solar cells set a new world record for efficiency of 26%
Cell efficiency TOPCoRE solar cells reached 26%, a new world record for double-sided contact solar cells.
A team of researchers led by Dr. Armin Richter from the Fraunhofer Institute for Solar Energy Systems has achieved a record conversion efficiency of 26.0% in a bi-contact silicon solar cell.facial. In a recently published Nature Energy article, "Design Rules for High-Efficiency Double-Sided Contact Silicon Solar Cells with Balanced Charge Carriers and Recombination Losses," Richter explains the structure of the record cell and proposes that aspects design fundamentals are even more effective. Designing the back surface of the cell with charge carrier collection passivation contacts across the entire surface is the key to success.
Solar cells made from crystalline silicon dominate the global photovoltaic market with more than 90% market share. Thanks to technological progress in recent years, their yield is already very close to the theoretical yield limit of crystalline silicon (29.4%). Previously, record efficiencies of around 26% were limited to solar cells with two metal contacts on the back, so-called celssolar cells with interdigitated rear contact or IBC. However, double-sided contact solar cells have established themselves as the industrial standard and become the first choice in industrial production due to their lower complexity.
Thanks to a new method for double-sided contact cells, solar cell researchers at Fraunhofer ISE have shown that it is also possible to achieve the highest efficiency of this type of solar cell .
The basis of the recording unit is TOPCon (Tunnel Oxide Passivated Contact) technology. Developed by Fraunhofer ISE, this technology combines the advantages of extremely low surface recombination losses with efficient carrier transport. Industry standard unitThere is a pn junction on the front side, while the pn junction in the recording unit forms a full surface TOPCon contact on the rear side. Consequently, doping with bore over the entire surface on the front face is no longer necessary, only allowing localized diffusion of boron just below the contact on the front face.
This TOPCoRE cell (TOPCon rear emitter solar cell) has higher voltage and higher fill factor compared to cells with a front collector emitter.
With this cell design, the wafer can be better used for transporting charge carriers, and the front side can be passivated more efficiently (aluminum oxide is used for this).
A detailed analysis of power losses shows that these cells generally compensate and minimize electron and hole transmission losses as well as transmission and recombination losses.
"Based on a system-based simulation analysis, we were able to derive some basic design rules for future solar cellsin high-efficiency silicon with efficiencies greater than 26%. Both sides of the contact solar cell have the potential to achieve an efficiency of 27%, surpassing the world record for silicon solar cells,” explains Professor Stefan Glunz, Director of Photovoltaics Research at Fraunhofer ISE. p>
The main advantage of the cell structure developed by Fraunhofer ISE is that the subsequent production step (connection of solar cells into modules) can be based on existing technology, so that many standard technologies can be used .
Reference:
Armin Richter et al. - side-contact silicon solar cells with balanced charge carrier transport and recombination losses, Nature Energy (2021/s41560-021-00805-w
).