Different production stages of the photovoltaic manufacturing industry have different requirements for the clean room cleanliness, primarily ranging from ISO 5 to ISO 7 clean room.

Photovoltaic industry in the raw material preparation stage (silicon refining, sorting, cleaning, etc.), usually need ISO 7 ~ 8 clean room;

Silicon wafer production (silicon ingot cutting into sheets and chemical etching) usually requires ISO 7  clean room;

Cell manufacturing stage: The film deposition, diffusion, lithography, etching process: ISO 5 clean room is required; Cleaning and coating process: an ISO 6 clean room is required;

Moduleencapsulation stage: Welding, laminating, framing process: Generally need ISO 6~7 clean room;

Encapsulation and testing processes: ISO 7 clean room is required;

  Is it necessary to prevent silicon wafer oxidation caused by excessive humidity?

  The temperature of photovoltaic wafer production and polysilicon treatment workshop is generally controlled at 22±2℃ and humidity is controlled at 35~45% (lithography process requires high temperature accuracy, temperature fluctuation does not exceed±0.5℃); In the encapsulation and testing workshop, the temperature can be controlled at 24±2℃ and humidity is controlled at 40~60%.

  High humidity in the workshop (> 60%) in the photovoltaic industry will lead to the surface oxidation of silicon wafers, accelerate the corrosion of metal parts, and cause the chemical adsorption of dust, which will directly affect the performance of photovoltaic devices. Therefore, the humidity should be strictly controlled.

The main reason for the need for electrostatic protection in the photovoltaic industry is that static electricity is easy to cause harm in the manufacturing process of photovoltaic modules.

Risks of static electricity to the manufacturing process of photovoltaic products:

1. Destruction of sensitive components: Electrostatic discharge (ESD) may lead to the breakdown of the photovoltaic cell internal microcircuit or performance decline. Especially in the diffusion, lithography and other high-precision processes, electrostatic interference will directly reduce the conversion efficiency of the battery;

2. Affect material stability: silicon wafer is easy to adsorb charged particles in electrostatic environment, leading to surface passivation layer damage or metal electrode oxidation, affecting the long-term reliability of components;

3. Easy to cause pollution: electrostatic adsorption will increase the attachment probability of dust particles in the air, affect the product surface quality; electrostatic may promote the residue of chemical reagents in the wet cleaning process, causing silicon wafer surface corrosion or uneven coating;

4. Hidden danger of safety production: for flammable gas (such as silane) in clean room, it may cause explosion accident and threaten the safety of personnel and equipment; in addition, electrostatic accumulation may cause instantaneous electric shock to operators and affect the operation stability.

Process requirements for the clean room:

5. Photovoltaic clean room usually needs to maintain humidity at 40%~60% (such as 55 ± 5% fordiffusion process) .Humidity too low will aggravate the accumulation of static electricity, andhumiditytoo high may cause silicon wafer oxidation, which needs to be accurately controlled by ion fan and other equipment.

Therefore, the photovoltaic industry clean room needs to do a good job of static electricity protection, to avoid the impact on product quality.

  What are the key considerations?

  Lighting design in photovoltaic clean room should meet production process requirements: Core process area (such as diffusion, lithography and detection area): the illumination shall be above 1000 Luxwhichmeets the requirements of fine operation and quality inspection; in general production area (such asencapsulation and cleaning process): the illumination shall be controlled at 300~500 Lux to balance energy consumption and operation visibility. The lighting fixtures should be evenly covered to avoid visual fatigue caused by the difference between light and shade. At the same time, anti-glare design (such as diffusion cover or teardrop lamp) should be adopted to reduce the interference of high brightness light source to precision operation.

  In the photovoltaic industry clean room, the color temperature of lighting lamps should be 5000~6000K cold white light to simulate the natural light environment and improve the operation accuracy, but for ultraviolet sensitive areas (such as photoresist coating), workshop lamps should choose yellow light to prevent ultraviolet-caused material deterioration.

The noise of non-unidirectional flow clean roomunder as-built statusin photovoltaic industry should be ‌≤60dB, and noise of unidirectional flow clean room should be‌≤65dB, so asto avoid affecting the accuracy of precision instruments and personnel operation.

To control clean room noise, firstly select low noise equipment (such as low noise fan and silent air compressor), install rubber vibration isolation pads at the base of the equipment, repair the equipment regularly, replace the worn parts to reduce the additional noise caused by mechanical friction; secondly, frequency conversion speed regulating device shall be installed and fan speed adjusted according to production requirements. The air duct system shall use impedance composite muffler for high noise equipment (such as vacuum pump) and high noise process (such as cutting and cleaning) working at different times to avoid overlapping noise at the same time.

In addition, the photovoltaic industry clean room decoration materials (partition wall, ceiling, floor, etc.) choose good sound insulation effect materials asmuchas possible.

Through the above measures, reduce the noise as far as possible to meet the dual requirements of production environment comfort and process accuracy.

  Photovoltaic industry exhaust gas treatment: photovoltaic industry welding, diffusion and other processes will have dustandwaste gas. It can be collected through theexhaust hood, exhaust louver and then filter, and then discharged to the outdoor through the exhaust fan; Organic waste gas produced in the workshop can behandled byactivated carbon adsorption-catalytic combustion integrated machine.The activated carbon adsorption saturationfollowing with regeneration by 200-400℃ catalytic combustion can haveVOCs Removal rateat98%; The acid-base gas produced in the workshop can be neutralized and discharged through acid fog tower and other equipment; besides, Some silane exhaust gas can betreated inexplosion-proof scrubber,using an inert gas dilution to reduce the risk of explosion. The concentration of the exhaust gas is controlled below 10% of the lower explosion limit (LEL).

  Waste water treatment of photovoltaic industry: Cutting / cleaning, etching / diffusion of photovoltaic industry will produce wastewater. Cutting / cleaning wastewater adopts multistage precipitationplus membrane filtration combination process to remove silicon powder and chemical residue; etching / diffusion wastewater selectively adsorbs heavy metals (such as lead and copper) by adding ion exchange resin, and removes trace organic matter with activated carbon adsorption. Wastewater treatment process is generally: pretreatment (grille intercept remove large particle impurities, acid and alkali neutralization pH measures), chemical precipitation (cooked lime + calcium chloride combined precipitation method), depth treatment (ozone oxidation, reverse osmosis (RO) membrane separation, etc.). Through the above process ofwastewater treatment, recycling of water resources can berealized.

  Different production stages of the lithium battery industry have different requirements for the clean room cleanliness, and the main requirements are the clean room cleanliness between ISO 5 and ISO 8.

Lithium battery industry in the positive and negative electrode batching, slurry pulling process usually needs ISO 8 clean room;

Coating, pole piece production, roller pressure cutting link need ISO7, local station need ISO5~6 clean room;

Rolling, assembly, liquid injection sealing link needs ISO7, key equipment process needs ISO5~6 clean room;

The capacity testing workshop usually requires an ISO 8 clean room;

  Lithium battery industry basically maintains the clean grade of ISO7 in the main workshop of battery production (from coating to cellencapsulation), and FFU can be uniformly arranged according to the ventilation times (25 times/h); the clean area of ISO5 should be maintained in important positions such as coating head, cutting, winding, lamination and so on. The FFU at the top of the equipment should be full and adopt one-way laminar air supply; the clean area of ISO6 should be maintained; FFU should be calculated as not less than 60 times/h, and adopt non-unidirectional air supply.‌‌

  In the lithium battery industry, controlling the temperature and humidity in clean rooms is crucial. The temperature in various workshops is typically maintained between 20°C and 25°C, with fluctuations kept within ±1°C. Different production processes have varying humidity requirements:

  Mixing and Coating Area: The relative humidity should be ≤30% to prevent the slurry from absorbing moisture, which could alter its viscosity.

  Rolling and Cutting Area: The relative humidity should be ≤20% to minimize micro-cracks on the surface of the electrode sheets.

  Stacking, Winding, and Assembly Area: The relative humidity should be ≤10% to avoid the risk of short circuits caused by damp separators.

  Baking, Electrolyte Filling, and Sealing Areas: The dew point temperature should be ≤-45°C, ensuring an ultra-low humidity environment to maintain the purity of the electrolyte.

The humidity control in the production workshop of the lithium battery industry is strict, the relative humidity is generally low (30%), the process environment and even the dew point temperature should be-45℃, and it is difficult to achieve this effect with ordinary air conditioning refrigeration dehumidification. The lithium battery industry mostly adopts therotary dehumidification system (frozen water +rotary double dehumidification). For ultra-low wet environment such as cell baking and liquid injection, the two-stage wheel dehumidification system (the first wheel is used for pretreatment (dew point-15℃), and the second-stage wheel depth dehumidification (dew point-45℃)).

  According to the different production process, the humidity controlrange is recommended as follows: workshop with 30% relative humidity (such as mixing, coating head, tail, etc.); workshop with 20% relative humidity (such as roller pressure, production); workshop with relative humidity of 10% (such as lamination, winding, assembly, etc.); workshop with dew point temperature-45℃ (e.g., cell baking, liquid injection, sealing, etc.). According to the different humidity requirements, choose the corresponding runner dehumidification unit. For workshops with relative humidity of 10-30% (dew point temperature above-15℃), chilled water + primary runner dehumidification system can be used; workshops with dew point temperature of-45℃ can adopt two-stage runner depth dehumidification system (primary runner pretreats fresh air, dew point-15℃, reduce the secondary runner load and secondary runner depth dehumidifier to-45℃) and use the partial closed environment to better ensure the dew point control to meet the process requirements.

Lithium battery clean room must ensure low humidity due to the process requirements, which is easy to produce static electricity accumulation. Anti-static protection is mainly started from several aspects:

1. The floor of the lithium battery clean room adopts an anti-static floor system (the resistance value of the ground surface should be controlled at 1x10⁶-1x10⁹Ω) to provide a stable electrostatic discharge path.

2. The workshop adopts anti-static materials, such as anti-static turnover containers (storing electrode materials and semi-finished products), and the working table is covered with anti-static rubber pads, etc.

3. Operators should wear anti-static clothing (surface resistance 1x10⁵-1x10⁷Ω), anti-static shoes (resistance 1x10⁵-1x10⁸Ω) and wrist belt (grounding resistance ≤35Ω) to remove the clothing surface static electricity through the electrostatic machine before entering the clean room.

4. The key station installation of ion air gun / ion rod and other equipment, through ionizing air to produce negative ions, neutralize the positive charge, to prevent static accumulation.

In addition, temperature and humidity sensors and static electricity monitoring equipment should be installed in key areas to monitor and record the data in real time. Once the humidity is found to be below the safety threshold or the static electricity level rises abnormally, measures should be taken to adjust immediately.

How is safety ensured?

The oxygen content control standard in the core area of the lithium battery clean room is:

Injection andencapsulation area: oxygen concentration should be ≤50ppm, using nitrogen filling and replacement process (purity ≥99.999%) combined with closed operation inglove box;

Pole coating and drying area: oxygen concentration ≤100ppm, prevent external air infiltration through local micropositive pressure design (5-10Pa);

The realization of low oxygen mainly depends on the inert gas circulation system: the glove boxplus gas purification unit (VPSA nitrogen generator) is used to monitor the oxygen concentration in real time and automatically replenish nitrogen. At the same time, a laser oxygen analyzer (precision±1ppm) is equipped to dynamically monitor the oxygen concentration.

The main safety guarantee measures are:

1. Environmental interlocking protection: oxygen concentration-equipment linkage: when oxygen concentration is >100ppm, automatically cut off liquid injection/encapsulation equipment power and start emergency nitrogen supplement; maintain positive pressure difference of 10-15Pa between clean room and external area to prevent oxygen backflow;

2. Explosion-proof and fire prevention design: use explosion-proof motor, explosion-proof lamps and other explosion-proof equipment to eliminate the risk of electric spark; set up negative pressure collection device, and control the electrolyte steam concentration below 5% LEL;

3. Personnel operation specification: Positive pressure air breathing apparatus (gas supply pressure≥0.5MPa) is required to enter the low oxygen area for ≤30 minutes; conduct emergency drillfor excessive oxygen concentration every quarter, and the response time is ≤3 minutes.