TOPCon cell technology has become one of the two leading next-generation options after mono PERC. But for the n-type architecture to truly become a rival to PERC, high-quality and cost-effective production technologies must become settled.

TOPCon, which otherwise goes by a variety of names, is an abbreviation of Tunnel Oxide Passivated Contacts. It involves depositing a nanometer scale layer of silicon oxide, by a thicker polycrystalline silicon layer, between the silicon wafer and metal contacts. The layers reduce charge recombination between the wafer and the contacts, increasing carrier lifetime and resulting in a conversion efficiency boost of around 0.5%.

One of the unanswered questions regarding  TOPCon is precisely which production processes will prove to be most effective in large-scale production. The Netherlands’ Tempress has been one of the most prominent equipment providers to  TOPCon producers in recent years via a long-running collaboration with TNO Energy Transition, formerly ECN – the Energy Research Centre of the Netherlands.

Tempress supplies low pressure chemical vapor deposition (LPCVD) tools for  TOPCon production. In September 2018, it announced that it was supplying Trina with its LPCVD poly equipment, however there have been no follow-up orders publicly announced since. At the time, Trina itself had reported supplying around 1 GW of Top Runner projects in China with modules deploying its n-type  TOPCon technology.

However, there can be downsides to LPCVD, and Trina engineers told pv magazine in December 2018 that it was experiencing frustrations in its  TOPCon processes, noting that production lines can be disrupted by pipe cracks and deposition reactors becoming “dusty” with “tiny silicon particles”.

“The market impact could and should be high, because  TOPCon is an upgrade to existing mono PERC lines,” noted Simon Price, the CEO of Exawatt. In providing context, Price noted that Exawatt formerly advised against atomic layer deposition (ALD) for PERC production, due to low throughput. However, once the throughput challenge was addressed, ALD quickly moved into mainstream production –based on its inherent advantages in terms of superior control of film thickness.

“So, if PECVD is an inherently better process, then you could make the argument that the productivity challenge can and will be known,” said Price.