L R AS Published on Monday 9 March 2020 - n° 312 - Categories:cells
To learn more about TOPCon technology
The TOPCon (Tunnel Oxide Passivated Contacts) cell manufacturing technology is one of the two current production options after PERC mono. However, high quality and cost effective production levels have not yet been achieved.
The world's largest project (105 MWp) using TOPCon N-type two-faced panels was installed in southern Oman. The panels were supplied by Jolywood. These panels accept higher temperatures than other cells and also offer a guaranteed 87.4% output power guarantee after 30 years of operation: this reflects the lower sensitivity of the N-type to light-induced degradation (LID).
TOPCon is an upgrade of existing mono PERC lines. In TOPCon technology, a thin layer of silicon oxide (at the nanometer scale) is deposited between the silicon wafer and the metal contacts, which is covered by a thicker layer of polycrystalline silicon. These layers reduce the charge recombination between the wafer and the contacts, increasing the lifetime of the substrate and leading to an increase in efficiency of about 0.5%.
Among the currently unanswered questions, it is not yet known which TOPCon production process will prove to be the most efficient in large-scale production. The Dutch company Tempress supplies low pressure chemical vapour deposition (LPCVD) equipment. This process can be disrupted by cracks in pipes and the deposition systems becoming dusty due to tiny silicon particles.
Meyer Burger recommends plasma-assisted chemical vapour deposition (PECVD) via its CAiA platform. This enables the TOPCon process to be industrialised for series production.
The speed of atomic layer deposition (ALD) has enabled a rapid transition to mass production as this system provides better control of film thickness.
BloombergNEF believes that a compromise will be found between quality and cost: "Basically, LPCVD is a thermal reaction, while PECVD is a low temperature alternative". "In terms of throughput, LPCVD is superior, but it can lead to cellular defects. In terms of thin film performance, PECVD does a better job on uniformity and thickness, but LPCVD looks more like a large-scale industrial solution.
Other production processes are advanced, such as Atmospheric Chemical Vapour Deposition at Atmospheric Pressure (APCVD). A Chinese supplier has developed LPCVD equipment. Improvements are constantly being made. In November 2019, Trina achieved global efficiency for its N i-TOPCon (industrial tunnel oxide passivated contact) cell. The 247.79 cm² cell achieved an efficiency of 23.2% on its front surface. Trina reported that this was with low cost equipment.
PV Magazine of 7 March
