How TOPCon is winning the market against HJT using TBC concept

?????????TOPCon (Tunnel Oxide Passivated Contact) was originally discovered, name-coined and published by ISFH, Germany a decade back. Typically, an N-type substrate is being used (to achieve higher efficiency) with a tunnel oxide of few ultrathin monolayers of SiO2 and a thin layer of doped Poly-silicon layer. The two together form a passivation contact structure, which effectively reduces surface recombination ultimately leads to higher efficiency compared to its predecessor PERC (Passivated Emitter Rear Contact).?According to ISFH calculations, the theoretical maximum efficiency of double-sided polysilicon passivated TOPCon cells is 28.7% (27.5% for HJT), and is closest to the theoretical limit efficiency of crystalline silicon solar cells at 29.43%, with great potential for efficiency improvement.

?????????While several Chinese companies, especially the Tier 1 companies like JINKO, Longi and Trina solar have got TOPCon technology into mass manufacturing adoption and announcements of Several 100s of GW are happening in real-time, while HJT manufacturers are still struggling to reduce the price in terms of $/Wp due to highest usage of silver paste, higher CAPEX and OPEX due to supply chain monopoly, etc. Jinko Solar announced that the full-area cell conversion efficiency of its self-developed 182mm2 N type high-efficiency monocrystalline silicon cell reached 25.7%, setting a new world record for the conversion efficiency of a large-area N-type monocrystalline passivated contact (TOPCon) cell.

?????????The production line has good compatibility and has the advantage of cost control between PERC & TOPCon. Compared with N-type TOPCon and P-type PERC, the difference in process route is mainly reflected in Ingot growth (P or N-type). With respect to cell line, the tunnel oxide deposition, boron diffusion and Polysilicon layer deposition equipment are added, while the upstream Polysilicon material, silicon Ingot-wafering and/or other heavy asset segments do not involve equipment replacement, and the existing P-type PERC equipment process is retained and utilized to the greatest extent and fully compatible for N-type TOPCon.?

?????????With most of the manufacturing companies are slowly moving from PERC to TOPCon, the innovation leader LONGI (who revolutionized the complete market from Multi to Monocrystalline wafer) came up with a different strategy of introducing P-IBC (they call it HPBC- Hybrid Passivated Back Contact), although the original version of N-IBC was marketed by SunPower. They have been into R&D of HPBC for last few years. The positive and negative electrodes of the IBC (interdigitated back contact, full back electrode contact crystalline silicon photovoltaic cell) are arranged on the backside of the solar cell in an interdigitated manner, and the PN junction is also located on the backside of the cell. There is absolutely no metal contacts on the front side to make the IBC cell to have a higher short-circuit current Jsc, and the back side can allow wider metal grid lines to reduce the series resistance Rs and improve the fill factor FF; plus the front surface field and good passivation of the cell will also bring Open circuit voltage gain, IBC cell has many advantages in reducing optical loss, improving efficiency, improving cell performance, and beautiful aesthetics.

?????????High theoretical conversion efficiency and low temperature coefficient are its inherent advantages. The researchers expect an efficiency record of 29.1 percent for the IBC solar cell. In addition, IBC solar cell technology?improves the temperature coefficient of the traditional option from -0.387%/oC to -0.446%/oC, down to -0.29%/oC. Therefore, IBC solar panels can provide better performance in hot climates. On the downside, the structure of producing such an innovative cell is rather complex leading to unreasonable yields and higher costs involved under manufacturing scenario. However, the deadly duo combination of TOPCon with IBC technology, seemingly known as TOPCon Back contact (TBC) is gaining huge attention after the introduction of HPBC concept by LONGI solar.

The HPBC concept introduced by LONGI Solar seems to have a better cost solution. In this concept, a P-type silicon wafer is used as the substrate, and boron doping is not required on the front and back, and no mask and Photolithography, with simple process steps, simplifies the complicated process of traditional IBC to 12 steps, and the production cost is significantly reduced. The name HPBC is derived for the reason that it’s a combination of TOPCon & IBC technology. Due to the success of this technology in Pilot scale, LONGI solar had recently announced an expansion plan of 50GW with this new HPBC technology.

With this new technology in place, more and more cell players are expected to stalk behind TOPCon route instead of HJT. More interestingly, it still uses P-type wafers instead of N-type to reduce the overall cost.