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    "title": "Low-Light Performance Showdown: TOPCon, BC, and HJT Backed by Real-World Data -  - Ooitech, the world's leading solar panel production line solutions provider, supply chain expert, solar panel making machine facotry",
    "description": "A data-driven comparison of low-light performance across TOPCon, BC, and HJT solar cells, examining the physics of shunt resistance and recombination alongside field-test evidence.",
    "keywords": "low-light performance, TOPCon, BC solar cell, HJT, shunt resistance, weak light response, solar cell efficiency, ideality factor",
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            "level": 2,
            "text": "Low-Light Performance Showdown: TOPCon, BC, and HJT Backed by Real-World Data"
        },
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            "level": 3,
            "text": "Low-Light Performance Showdown: TOPCon, BC, and HJT Backed by Real-World Data"
        },
        {
            "level": 5,
            "text": "Introduction"
        },
        {
            "level": 5,
            "text": "The Physics of Low-Light Response: Who Leaks and Recombines Less"
        },
        {
            "level": 6,
            "text": "The most critical factor: shunt resistance Rsh"
        },
        {
            "level": 6,
            "text": "Secondary factor: ideality factor n"
        },
        {
            "level": 6,
            "text": "Series resistance Rs matters less here. Power loss across Rs is I²R; under low light the current is small, so its relative impact weakens."
        },
        {
            "level": 5,
            "text": "Why BC Is Weaker Under Low Light: A Structural Reason"
        },
        {
            "level": 5,
            "text": "Field Evidence: TOPCon Beats BC in Per-Watt Output Under Low Light"
        },
        {
            "level": 5,
            "text": "Don't Confuse Temperature Coefficient With Low-Light Response"
        },
        {
            "level": 5,
            "text": "How to Judge a Cell's Low-Light Quality on the Production Line"
        },
        {
            "level": 5,
            "text": "Summary"
        },
        {
            "level": 5,
            "text": "Tags :"
        },
        {
            "level": 5,
            "text": "Category"
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        {
            "level": 5,
            "text": "Recent Post"
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        {
            "level": 6,
            "text": "What Is TOPCon Solar Cell? A Complete Guide to Tunnel Oxide Passivated Contact Technology"
        },
        {
            "level": 6,
            "text": "Understanding the Three Major PV Cell Technologies: TOPCon, HJT, and Perovskite"
        },
        {
            "level": 6,
            "text": "THBC Solar Cell Technology: How Hybrid Passivated Back Contact Breaks the 28% Efficiency Barrier"
        },
        {
            "level": 6,
            "text": "Low-Light Performance Showdown: TOPCon, BC, and HJT Backed by Real-World Data"
        },
        {
            "level": 6,
            "text": "BC, IBC, TBC, HBC, HPBC... What's the Connection Between All These BC Technologies?"
        },
        {
            "level": 5,
            "text": "Popular Tags"
        },
        {
            "level": 3,
            "text": "Request A Quote"
        },
        {
            "level": 2,
            "text": "We deliver expertise you can trust our service"
        },
        {
            "level": 3,
            "text": "Cost-Effective Advantages"
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        {
            "level": 3,
            "text": "Our Experience Team"
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        {
            "level": 3,
            "text": "15+ Years Industry Experience"
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            "level": 2,
            "text": "What Our Client Say's about us"
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            "level": 3,
            "text": "KTECH"
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        {
            "level": 3,
            "text": "Jizzakh Polytechnic Institute"
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        {
            "level": 3,
            "text": "Amjad"
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        {
            "level": 3,
            "text": "Mark"
        },
        {
            "level": 2,
            "text": "Our Latest Products"
        },
        {
            "level": 3,
            "text": "Soldering Ribbon & Flux – PV Cell Interconnection Materials"
        },
        {
            "level": 3,
            "text": "SS-2500B Full Automatic Solar Cell Tabber Stringer Machine - High-Speed Production Line Equipment"
        },
        {
            "level": 3,
            "text": "Offline String EL Tester OPT-S110H - Solar Cell String Electroluminescence Testing Equipment | Ooitech"
        },
        {
            "level": 3,
            "text": "Solar Panel Aluminum Frame – Anodized, G1/M6/M10/M12 Sizes"
        },
        {
            "level": 3,
            "text": "Non-Destructive Solar Cell Laser Cutting Machine - Advanced TCS Technology for High-Efficiency Cell Production"
        },
        {
            "level": 3,
            "text": "Automatic Solar Cell Layup Machine - High Speed MBB Half-Cell String Laying Equipment for Solar Panel Production Line"
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    "markdown": "# Low-Light Performance Showdown: TOPCon, BC, and HJT Backed by Real-World Data -  - Ooitech, the world's leading solar panel production line solutions provider, supply chain expert, solar panel making machine facotry\n\n> A data-driven comparison of low-light performance across TOPCon, BC, and HJT solar cells, examining the physics of shunt resistance and recombination alongside field-test evidence.\n\n![Low-Light Performance Showdown: TOPCon, BC, and HJT Backed by Real-World Data](https://cdn.ooitech.com/static/upload/image/20260624/1782293977288302.webp)\n\n- ** 2026-06-24\n- ** 0 Views\n- ** [Blog](/Blog.html)\n\n### Low-Light Performance Showdown: TOPCon, BC, and HJT Backed by Real-World Data\n\n##### Introduction\n\n> Nameplate power is a rated value; low-light response is real-world performance. Across most regions of the world, irradiance stays below 1000 W/m² for over 90% of the time. Only two or three hours around solar noon come close to STC conditions. Sunrise, sunset, overcast skies, rain—cells spend most of their working life under low light. A high rated efficiency does not guarantee high real-world output. Today we break down low-light response: who wins on physics, who proves stronger in the field, and how to judge a cell's low-light quality right on the production line.\n\n##### The Physics of Low-Light Response: Who Leaks and Recombines Less\n\nFrom the diode equivalent circuit, the root cause of efficiency drop under low light is simple: **the photogenerated current shrinks, but leakage and recombination do not shrink proportionally, so their relative share grows.**\n\n###### The most critical factor: shunt resistance Rsh\n\nUnder low light the photogenerated current drops sharply, but the leakage current stays roughly constant (it depends on voltage and Rsh). A larger share of leakage current pulls Voc down, which drags FF down, which lowers efficiency.\n\n**The higher the Rsh (the smaller the leakage), the better the low-light response. This is the core physical factor.**\n\n| Cell Type | Rsh Characteristics | Low-Light Performance |\n| --- | --- | --- |\n| HJT | i-a-Si:H passivation layer with excellent insulation, extremely low interface recombination | Best |\n| TOPCon | Positive and negative poles split across front and back, few edge isolation zones, controllable leakage paths | Good |\n| BC | Rear interdigitated structure, many P⁺/N⁺ isolation trenches, increased edge leakage risk | Weaker |\n\n###### Secondary factor: ideality factor n\n\nThe ideality factor reflects the recombination mechanism: n=1 for ideal diffusion current, n=2 when depletion-region recombination dominates. The larger n is, the heavier the recombination loss under low light. TOPCon's passivated contact structure gives n≈1.1-1.2, BC's rear interdigitated PN junction has more interface recombination channels at n≈1.2-1.4, and HJT's amorphous-silicon passivation excels at n≈1.0-1.1.\n\n###### Series resistance Rs matters less here. Power loss across Rs is I²R; under low light the current is small, so its relative impact weakens.\n\n##### Why BC Is Weaker Under Low Light: A Structural Reason\n\nBC places both positive and negative electrodes on the rear, requiring numerous isolation trenches between the P⁺ and N⁺ regions to achieve electrical separation. These trenches bring two problems:\n\n- **Edge leakage risk**: Trench etching can damage the silicon substrate and form leakage paths. A single BC rear surface holds hundreds of isolation trenches, each a potential leakage route.\n- **Interface recombination**: The P⁺/N⁺ interface area of the rear interdigitated structure grows larger, adding recombination centers and pushing the ideality factor n higher.\n\n**This is an inherent structural challenge, not a question of \"who did it badly.\"** Process optimization (controlling trench morphology, improving passivation layers) can help, but the structure puts BC at a natural disadvantage on this point.\n\nThe reason HJT performs best under low light is the opposite: the intrinsic amorphous-silicon i-a-Si:H passivation layer delivers outstanding surface passivation, low interface state density, the highest Rsh, and the smallest ideality factor.\n\n##### Field Evidence: TOPCon Beats BC in Per-Watt Output Under Low Light\n\nThe field data from several test institutes points in a consistent direction:\n\n| Test Institute | Location | Scenario | TOPCon vs BC Low-Light Gain |\n| --- | --- | --- | --- |\n| CPVT | Yinchuan, Ningxia | Morning/evening low-light periods | Overcast +3.89%, sunny +2.33% |\n| CPVT | Yinchuan, Ningxia | Extreme low irradiance (0-100 W/m²) | +4.38% |\n| TÜV Nord | Kagoshima, Japan | <400 W/m² | +10.79% |\n| TÜV Rheinland | Chengdu | 90% overcast/rainy days | +2.37%, morning/evening peak +7.18% |\n| CGC | Hainan | 127 days including 76 rainy days | +7.83% |\n| State Grid | Zhangbei | 200 W/m² | +2.6% |\n\n**Under low-light conditions, TOPCon's per-watt output exceeds that of BC, and the lower the irradiance, the wider the gap.**\n\nBut variation within the same technology route is also large. Multi-supplier comparison testing by Carbon Search Evaluation Lab shows BC products losing **2.78% to 6.57%** at 200 W/m² low irradiance, while TOPCon ranges from **2.14% to 4.72%**. **The gap between the \"best products\" of the three technologies is smaller than the gap between \"good products vs. poor products\" within the same route.**\n\nProduction takeaway: **when selecting, a manufacturer's process level matters as much as the choice of technology route.**\n\n##### Don't Confuse Temperature Coefficient With Low-Light Response\n\nTemperature coefficient and low-light response are two independent parameters, but they are easily mixed up.\n\n| Parameter | Relevant Scenario | HJT | TOPCon | BC |\n| --- | --- | --- | --- | --- |\n| Temperature coefficient | High-temperature scenarios (module >50°C) | -0.24%/℃ | -0.29%/℃ | -0.26%/℃ |\n| Low-light response | Low-irradiance scenarios (<400 W/m²) | Best | Good | Weaker |\n\nOn a hot, overcast summer day, high temperature and low light stack together, and HJT leads on both, compounding its advantage. On a cold, overcast winter day, low temperature reduces the influence of the temperature coefficient, and low-light response takes the lead. **Don't use the temperature coefficient to explain low-light performance, and don't infer the temperature coefficient from low-light performance—they are two distinct physical quantities.**\n\nLow-light optimization and UVID resistance are not inherently physically mutually exclusive either. Low light depends on electrical loss mechanisms (Rsh, n), while UVID depends on material stability (passivation-layer chemical bonds, encapsulant film). The two can be improved separately through independent optimization.\n\n##### How to Judge a Cell's Low-Light Quality on the Production Line\n\n**The most direct indicator: shunt resistance Rsh.**\n\nIn I-V testing, the higher a cell's Rsh, the more likely it performs well under low light. If a batch shows a wide Rsh distribution with a high proportion of low-Rsh cells, low-light output will surely suffer.\n\n**Special note for BC lines**: cells showing abnormal bright spots in the isolation-trench regions on EL images are likely to have low Rsh. This corresponds to the \"trench edge leakage\" mentioned earlier—a problem the structure is naturally prone to.\n\n**TOPCon lines**: Rsh above 1000 Ω·cm² is generally normal; below 500 calls for investigating edge isolation or pinholes in the passivation layer. Cells with excellent low-light behavior usually show Rsh above 3000.\n\n**HJT lines**: Rsh is naturally high, and above 5000 is common. But a low Rsh on an HJT cell usually means something has gone wrong at the TCO and a-Si:H interface.\n\n##### Summary\n\n> The physics ledger of low-light response: HJT is best, TOPCon is good, BC faces structural challenges. The field ledger: under low light, TOPCon's per-watt output really does exceed BC's, and the lower the irradiance, the wider the gap. But don't judge by technology route alone—the gap between good and poor products on the same route is even larger than the gap between routes.\n\n**Data sources**: CPVT Yinchuan field test (2025), TÜV Nord Kagoshima field test, TÜV Rheinland Chengdu field test, CGC Hainan field test, State Grid Zhangbei field test, Carbon Search Evaluation Lab multi-supplier comparison testing (2025).\n\n**Ooitech's view**: Real-world low-light output, not nameplate efficiency, is the true measure of a solar cell, and shunt resistance is the single factor that decides it most.\n\n---\n\n##### Tags :\n\n\n![](/template/ooitech/assets/img/shape/06.png)\n\n![](https://cdn.ooitech.com/static/upload/image/20250909/1757399770541443.webp)\n\n### Request A Quote\n\nAll uploads are secure and confidential.\n\n## We deliver expertise you can trust our service\n\nDirect-from-Factory Equipment.\n\n![](/template/ooitech/assets/img/icon/money-2.svg)\n\n### Cost-Effective Advantages\n\nWe deliver exceptional value, maximizing results while optimizing budgets for clients.\n\n![](/template/ooitech/assets/img/icon/staff.svg)\n\n### Our Experience Team\n\nOur skilled professionals specialize in innovative solutions and tailored strategies.\n\n![](/template/ooitech/assets/img/icon/certified.svg)\n\n### 15+ Years Industry Experience\n\nDeep expertise ensures reliable, trend-aware, and proven outcomes for success.\n\n![](https://cdn.ooitech.com/static/upload/image/20250910/1757477357667605.webp )\n\n![](https://cdn.ooitech.com/static/upload/image/20250910/1757477724911512.webp)\n\n![](/template/ooitech/assets/img/shape/06.png)\n\n## What Our Client Say's about us\n\nClient testimonials praise our deep understanding of their challenges, which leads to innovative solutions and strong ROI. 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