Advantages of HJT heterojunction compared to PERC and TOPCon

1. Comparison of HJT Advantages

Compared to PERC and TOPCon, HJT batteries have seven obvious advantages, including the following:

(1) Short production process → higher yield and lower labor and operation and maintenance costs: HJT’s core process only has four steps, namely, cleaning and velvet making, amorphous silicon film deposition, TCO film deposition, and metal Polarization density, which is significantly simplified compared with PERC and TOPCon batteries. A shorter process flow helps to improve the yield rate of production, while reducing labor, operation and maintenance costs.

(2) Adopting low-temperature process → reducing thermal damage: HJT is manufactured in an environment below 200 ℃ throughout the process, while the temperature of the PERC phosphorus expansion process needs to be higher than 850 ℃, while the temperature of the TOPCon boron expansion process needs to be above 1100 ℃. The low-temperature process helps to reduce thermal damage during the preparation of silicon wafers and save fuel.

(3) High double-sided rate → higher power generation: HJT batteries have a double-sided symmetrical structure, with a maximum double-sided rate of up to 90%; Both PERC and TOPCon require back polishing of silicon wafers during the preparation process, with a maximum double-sided rate of only 75% and 85%. A higher double-sided rate can increase the back power generation of HJT.

(4) Low temperature coefficient → higher power generation: HJT has a temperature coefficient of -0.24%/℃, which is lower than PERC (-0.35%/℃) and (TOPCon -0.30%/℃). Therefore, HJT has less energy loss and higher power generation in high-temperature environments.

(5) Low attenuation rate → higher power generation: The first attenuation of HJT is 1%, and the linear attenuation is 0.25%, which is lower than that of PERC and TOPCon. This is mainly due to the absence of PID and LID effects in HJT, which leads to higher power generation in the long life cycle of 25 years.

(6) More suitable for perovskite layering → greater efficiency potential: HJT batteries mainly absorb infrared light, while perovskite batteries have a higher utilization rate of light waves from short to visible wavelengths. The stacking of the two completes the “integration” of absorption spectra, which can open the ceiling of theoretical conversion efficiency.

(7) Easier to achieve thinness → larger cost reduction space: HJT’s double-sided symmetrical structure reduces the mechanical stress of the silicon wafer and improves the overall wafer rate during the preparation process; The low-temperature process also reduces the possibility of silicon wafer warping during heating, which is more conducive to the process of thinning.

TOPCon Technology Process

TOPCon technology: TOPCon adopts a composite structure of back oxide layer and doped polycrystalline silicon, forming good passivation contact and comprehensively improving the performance of the battery.

In situ doping and non in situ doping: There is not much difference in performance between the two options, but from the perspective of subsequent treatment after doping, in situ doping is currently a relatively compromise choice, the easiest and most stable choice for mass production, and has good controllability.

PE and LP: The PE route has congenital problems that do not reflect the advantages of TOPCon. Poly deposits quickly and has poor density, resulting in low efficiency of batteries made of PE. From a mass production perspective, LP has already met the demand and will be the mainstream in the future.

Comparison of N-type and P-type technical paths and difficulties: The P-type is much easier to perform TOPCon, but the efficiency improvement is not significant, only about 0.5 pct higher than the P-type PERC. This is mainly a problem with charge carriers. P-type charge carriers are holes, making transitions relatively difficult, while N-type charge carriers are electrons, so currently the mainstream choice is N-type.

Feasibility of combining TOPCon with IBC: N-type silicon chip has inherent advantages. TOPCon technology can be integrated with HJT and IBC Technological convergence, but TOPCon is still in a stage of being able to do, rather than a stage of good technology.

2. Comparison between TOPCon and PERC

Advantages:

High efficiency: TOPCon currently has the highest mass production efficiency among manufacturers, with an efficiency of up to 24.8%. The current mainstream PERC is 23.2%, and TOPCon is 1.6 percentage points higher. It is expected that by the second half of 2023, TOPCon will reach 26.8%, and the efficiency of PERC will be around 23.5%, with an efficiency difference of 3.3 percentage points.

Low attenuation: On the one hand, there is no dropout of TOPCon batteries, while the current testing efficiency of PERC batteries has dropped by 1-2 levels after a period of retesting; On the other hand, for the component side, there is no attenuation of TOPCon’s power generation, and PERC has a power attenuation of nearly 8% in its first year.

Long wave response is good: PERC only responds well to short waves, while TOPCon responds well in both long and short waves. TOPCon is not affected by the weather, and its power generation continues to be guaranteed, while PERC’s power generation is severely affected by the weather.

Disadvantages:

High fixed investment: TOPCon equipment investment is 200 million yuan/GW, while PERC is 120 million yuan/GW.

The process is complex: TOPCon has 12 steps, while PERC has 11 steps. TOPCon has added three new processes, deleted two processes, and adjusted one process. However, the new processes are relatively complex and difficult to control.

High non silicon cost: Currently, the non silicon cost of TOPCon is 0.26-0.27 yuan/W, and the cost of PERC is around 0.2 yuan/W. TOPCon is 30% higher than PERC, and it is expected that the cost of TOPCon will be 20% higher than PERC after both costs are reduced.

3. Comparison between TOPCon and HJT

Advantages:

Mature technology and good compatibility: TOPCon’s technology is relatively mature and has good compatibility. Out of the 12 processes, 8 processes are exactly the same as PERC. Among the newly added three processes, the designed operations, process windows, parameter settings, etc. are very similar to the original PERC.

Low workshop investment: TOPCon equipment investment is 200 million yuan/GW, while HJT currently needs to achieve a target of 300 to 350 million yuan/GW.

Good mass production: TOPCon’s operators and process equipment can seamlessly connect directly from the existing PERC workshop, without the need for additional training or skill upgrades.

High efficiency: Currently, TOPCon has a 0.4pct higher efficiency than HJT, and it is expected that the efficiency difference may widen by 2023.

Low non silicon cost: TOPCon is 0.26-0.27 yuan, while HJT is currently 0.33 yuan.

No attenuation of the battery: TOPCon has no attenuation of either the battery end or the components, but the efficiency of HJT gradually declines because of the use of low-temperature gel.

Disadvantages:

Long process flow: TOPCon has 12 steps, while HJT only has 5 steps (cleaning velvet, doping crystal silicon, conductive film, screen printing, testing and sorting). The longer the process flow, the greater the personnel and process complexity associated with the equipment.

The workshop occupies a large area: the long process flow results in a large amount of equipment required, and the land occupation area is large. At the same time, the equipment power cost of the entire engineering workshop will also increase accordingly.

Small reduction in silicon wafer thickness: PERC’s silicon wafer thickness ranges from 170 to 175 μ Between m (if the thickness is reduced too much, the stress in the aluminum backing plant will cause the strength of the silicon wafer to not meet the standard), TOPCon currently can achieve a mainstream of 150-155 μ M (To face the test of ultra-high temperature and severe temperature rise and fall caused by boron expansion, the subsequent thinning should not be too much), HJT currently has mainstream laboratory batches ranging from 110 to 120 μ Between m, there are very few other manufacturers that can achieve 90% μ About m. TOPCon saved about 20 μ Thickness of about m, while HJT saves 60 μ About m.

The size of silicon wafers is limited: The current mainstream size of TOPCon is 182210, and the resistance is relatively high. The main resistance comes from the area of the battery panel and component ends. However, HJT is limited by the process and can prioritize the 210 size.

Problems encountered in HJT mass production:

Low temperature silver slurry: The extremely low temperature of 250 degrees Celsius results in poor metallization of the silver slurry, which brings many derivative problems. The biggest point is that the welding tension of the components is completely not up to standard.

TCO film: TCO film is particularly prone to aging, and its performance deteriorates significantly after aging. The lifespan of PERC and TOPCon battery modules is generally 15-20 years, while the lifespan of the TCO film in HJT technology under harsh laboratory conditions is 3-5 years.

PVD&RPD equipment: The equipment comes from semiconductors and requires precise control, but its continuous operation ability is not high.