TOPCon technical difficulties

Difficulties in the TOPCon process

Boron diffusion

LPCVD winding plating problem

PE-poly film burst problem

Yield loss due to long process steps

Burn-through and diffusion destroy passivation

The high-temperature process causes damage to the silicon wafers

TOPCon cost difficulties

The consumption of double-sided silver is higher

Low yield

Low CTM

It is difficult to improve efficiency

The equipment maintenance quota is high

It is difficult to reduce the price of equipment

Process difficulty 1: boron expansion

BBr3/BCl3 diffusion with poor uniformity

The diffusion time is long (3.5 h), and the B expansion time is about 1 times longer than that of phosphorus diffusion

Using BCl3 instead of BBr3 has a stronger bond, which requires a high temperature duration of more than 3 hours, and it is difficult to thin the silicon wafer

In order to shorten the time, it is necessary to add a water cooling device to shorten the cooling time (30-50 minutes).

The high diffusion temperature (1000~1250°C) leads to serious damage to the silicon wafer

The longitudinal distribution of B atoms is poor

Solubility of solids

The junction depth is up to 1 um, and the carrier recombination is serious

Atomic radius

B: 0.85 amy

Si: 1.1 angstrom

P: 1.0 Angstrom

The large difference in the atomic radius between boron and silicon can easily lead to lattice distortion and more dislocations

OSF oxygen rings are easy to induce, and dislocation rings in the crystal pulling process are easily induced in oxygen atmosphere, and are shown as concentric circles under PL/EL

High temperature ←→ small atoms ←→ high oxygen content

Process difficulty 2: deposition of doped polysilicon

LPCVD is difficult

The rate of in-situ doping is too slow

Mature route: first deposit intrinsic poly→ then phosphorus expansion

Winding problems caused by single-sided coating - Winding plating greatly reduces the yield rate

Double-sided coating can improve yield – resulting in a doubling of the number of equipment

Pipe walls and quartz parts are heavily soiled – equipment maintenance is too frequent

PECVD is immature

Uniformity issues

H content is too high - hydrogen burst film blister

Contamination of tube P – tube P is a hot wall

Cleaning the chamber and carrier plate is too frequent

Process difficulty 3: two types of burn-through

Category I: Doped element burn-through

The poly layer doped P penetrates the SiOx layer, and the passivation decreases

Category II: Metal paste burn-through

Back: Poly silicon layer back silver paste burns through, resulting in a decrease in passivation

Front: PN junction burn-through, leakage

HJT technical difficulties

Difficulties in the HJT process

Maintain the cleanliness of silicon wafers before and after PECVD

Balance between VHF deposition uniformity and high throughput

Battery stability

HJT cost difficulties

The cost of silver paste is high

Low CTM

The cost of equipment is higher

Potential price increases for ITOs

HPBC technical difficulties

HPBC technical difficulties

Three-way alignment (laser 1/2, silk screen aluminum)

Post-texturing process (double throwing + post-texturing)

Yield degradation due to Ag burn-through (hot spots, leakage current, short circuits)

Component connection technology

Without a front-field FSF, it is not possible to push the carriers to the back, which will reduce efficiency

Parasitic leakage in the inverse zone

The aluminum back field compound is serious

HJT cost difficulties

Low yield

No data is available for CTM

Efficiency improvement bottlenecks