• Jolywood currently operating at average cell efficiency of 23.5% and 24.2%, but has strong roadmap to raise the production efficiency to 25.5%
  • Chinese company is also working on next generation n-type cell technologies as n-TBC and tandem cell structure using perovskites to reach efficiencies of 26% and beyond
  • NTOPCon modules, claims the company, are free from LID and have negligible power loss due to LeTID
  • For p-type, ISFH sees 27% power conversion efficiency potential for passivated contacts structures
  • ISFH found efficiency potential of 23.3% for back junction and 24% for IBC structures in its simulation results based on industrial process sequence with a potential of saving silver

In a webinar organized by TaiyangNews on the Potential and Recent Developments of High Efficiency N-type Passivated Contact (TOPCon) Solar Cell Technologies, Jolywood’s R&D director Chen Jia presented the progress of the n-TOPCon technology of the company. In addition to being a world leading backsheet supplier, Jolywood is also a leading cell and module producer in the field of  n-TOPCon.

Owing to its high efficiency and growth potential – the high efficiency n-type segment is growing at a rate of more than 30% – , Jolywood is exclusively focusing on n-type. Though the Chinese company started with n-PERT, since the technology cannot compete with PERC, the company started development in two directions – passivated contacts and IBC. It is currently operating a passivated contacts cell and module production facility with a capacity of 2.4 GW and 3 GW, respectively.

Toward cell efficiencies of 25.5%

Jolywood has also been mass-producing IBC cells for over a year with total shipments reaching 100 MW so far. Both cell technologies have attained an average efficiency of 23.5% in production, while its best passivated contacts cell recorded 24.2% in R&D. As part of development roadmap to increase the efficiencies to 26% and beyond, Jolywood is working on combining the high Voc attribute of the passivated contacts, which is more than 700 mV attained by Jolywood, with high currents attained for IBC structure using a so called n-TBC design. This design can increase the efficiency above 25%. Parallelly, the management is also evaluating the possibility of stacking perovskite with n-type technology.

Jia presented a roadmap to increase the efficiency of NTOPCon from the current level of 23.52% in mass production to 25.52% in the next 5 years by different area such as metallization, emitter formation and etc. “There are also a lot of challenges, for example on p+ side, how to implement the selective emitter (SE) structure and realize p+ poly, which are challenging, especially to implement in mass production,” said Jia. Similar to any other n-type technology, Jolywood’s passivated contacts products are also immune from light induced degradation (LID).

However, when it comes to another big concern of LeTID (light and elevated temperature induced degradation), the technology is not completely free, though the impact is minimal. Jolywood has tested its modules under different test conditions, the degradation due to LeTID is less than 0.5%, it showed in the webinar. “We even observed slight power gains in few instances,” added Jia.  Jolywood is currently offering the NTOPCon half cell modules in three variants – 120, 144 and 156 cells with power rating of 350 W, 415 W and 450 W, respectively. These modules have an efficiency between 20.67% and 20.73%. Jolywood has supplied its modules for various applications around the world for ground mount as well as for rooftop applications.

Passivated contacts on p-type

While Jolywood presented the industrial perspective about the passivated contacts technology, ISFH represented the academia side in the TaiyangNews webinar. Felix Haase, project manager at ISFH provided an overview about the potential of the passivated contacts technology. ISFH calls its technology POLO that stands for Poly-Si on Oxide. ISFH has attained a world record efficiency of 26.1% with its POLO technology adapted to IBC structure on p-type base wafer and according to the simulations, the cell structure has a realistic efficiency potential of 27%.

Contacts combinations: ISFH’s Haase presented the choice for contacts and resulted efficiency corresponding combination of contacts. He said p-diffused contacts limit the cell efficiency and eliminating these increases the efficiency potential to about 27%, close to 3% points higher.

Contacts combinations: ISFH’s Haase presented the choice for contacts and resulting efficiencies in correspondence to combinations of different contacts. He said p-diffused contacts limit the cell efficiency and eliminating these increases the efficiency potential to about 27%, which is close to 3% points higher.

As for the industrialization of the technology, Haase presented different combinations of cell structures and emphasized that the efficiency of p-type silicon substrate is always limited with phosphorus diffused emitter to a maximum of 25%. It is therefore recommended to replace the phosphorus diffused emitter with different structures using polysilicon and still using aluminum as the metal for contacting aluminum that can lead to efficiencies of up to 27%.

ISFH has developed industrial POLO-BJ (back junction) cell and POLO-IBC based on p-type wafer using same process equipment as PERC with an additional polysilicon deposition tool. The POLO-BJ uses silver only on one side, as aluminum is also used for one side. The process flow eliminates boron diffusion and uses only high temperature step. Based on simulated results, POLO-BJ has an efficiency of 24.3% and POLO-IBC structure 25%, and Haase is optimistic that 1% point below the simulation level is possible to attain in production.

About passivated contacts

With practical PERC efficiencies expected to reach the threshold soon, PV manufacturers have stated looking into new cell technologies beyond PERC. Passivated contacts, also widely known as TOPCon, a brand name for a proprietary technology developed by Fraunhofer Institute of Solar Energy (Fraunhofer ISE), is shining bright on many leading cell maker’s radar’s technology roadmaps.

The technology is aimed at addressing one main shortcoming associated with the cell architectures mentioned above. Metal contacts formed in most of these approaches are highly recombination-active and cause losses. This can be avoided by electronically separating contacts from the absorber by inserting a wider bandgap layer. Based on this principle, researchers have developed a ‘selective’ passivated contacts made of a tunneling oxide enabling majority charge carriers to pass and prevent minority carriers from recombining.

The selective here means the principle can be applied on the front and/or rear of the cell. However, today’s industrial practice is to apply the passivated contacts scheme to the rear side of the n-type solar cell. Though the interest is high, only few companies have been able to manage to enter mass production and Jolywood is at the forefront in development of passivated contacts technology.

A recording of the TaiyangNews webinar ‘Potential and Recent Developments of High Efficiency N-type Passivated Contact (TOPCon) Solar Cell Technologies’ and the presentation are accessible here