HJT VS BC
HJT (Heterojunction) and BC (Back Contact) are two high-efficiency battery technologies that are currently attracting much attention in the photovoltaic field, representing different technical routes and market positioning. The following is a comparative analysis from the aspects of technical principles, performance, cost, industrial chain, etc.
Technical Principles And Core Differences
1. HJT (Heterojunction Technology)
Principle:
Amorphous silicon (a-Si) thin film is deposited on both sides of N-type monocrystalline silicon wafers to form a PN junction, combining the heterogeneous structure of crystalline silicon and amorphous silicon.
Core features:
Low-temperature process (≤200℃), compatible with thin silicon wafers (100-130μm), and reduced silicon material consumption.
High bifaciality (85%-95%), excellent weak light performance, suitable for distributed photovoltaics (such as rooftops, BIPV).
No metal grid lines (or only fine grids) on the surface, beautiful appearance, suitable for high-end markets.
Representative technologies:
Pure HJT (such as Maxsun, Tongwei, Trina Solar), stacking technology (HJT + perovskite, laboratory efficiency exceeds 33%).
2. BC (Back Contact Technology, Back Contact)
Principle:
The positive and negative electrodes (P-type and N-type regions) and metal electrodes of the battery are all integrated on the back of the battery, and there is no grid line blocking the front to improve light absorption.
Core type:
IBC (Interdigitated Back Contact): such as SunPower's Maxeon technology.
HPBC (hybrid passivation back contact, independently developed by LONGi): Combining TOPCon passivation technology with BC structure, the efficiency is further improved.
Core features:
The process is complex, requiring high-precision lithography and mask technology (12-16 processes), and high equipment precision requirements.
There is no grid line on the front, and the appearance is extremely beautiful, suitable for high-end distributed (such as household, industrial and commercial roofs) and high-efficiency components.
It can be combined with TOPCon (such as LONGi HPBC) or HJT to form "TOPCon-BC" or "HJT-BC" stacking technology.
Key Performance Comparison
|
Indicators |
HJT |
BC (taking HPBC as an example) |
|
Laboratory efficiency |
26.8% (Japan Kaneka, 2023) |
27.6% (Longi HPBC, 2024) |
|
Mass production efficiency |
24%-25% (mainstream in 2024) |
25%-26% (Longi Hi-MO 7 series) |
|
Temperature coefficient |
-0.25%/℃ (excellent, suitable for high temperature areas) |
-0.28%/℃ (slightly inferior to HJT) |
|
Bifaciality |
85%-95% (highest in the industry) |
75%-85% (affected by the back electrode layout) |
|
Weak light performance |
Excellent (obvious power generation advantage under low irradiance) |
Excellent (no front grid line, more sufficient light absorption) |
|
Degradation rate |
<2% in the first year, annual attenuation 0.25% (strong stability) |
<2% in the first year, annual attenuation 0.3% (close to HJT) |
Cost And Industrial Chain
1. HJT Advantages and Challenges of BC
Advantages:
Few processes (only 4 steps: cleaning and texturing, amorphous silicon deposition, TCO film layer, metallization), high degree of automation.
Great potential for thinning silicon wafers (target below 100μm), reducing silicon material costs (accounting for 40%-50% of component costs).
Strong compatibility, easy to stack with perovskite, theoretical efficiency limit exceeds 35%.
Challenges:
High equipment investment (single GW equipment cost is about 800-1 billion yuan, which is twice that of PERC), and dependence on imports (such as Japan's AMAT and China's Maxwell).
A large amount of silver paste is used (accounting for 30% of the battery cost), and copper electroplating substitution needs to be promoted (cost reduction of more than 50%, but mass production is not yet mature).
2. Advantages and Challenges of BC
Advantages:
Extreme efficiency (leading single-cell efficiency, suitable for high-end market premium), grid-free design improves the aesthetics of components.
It can be combined with existing TOPCon technology (such as HPBC), reuse some equipment (such as diffusion furnace, PECVD), and lower the investment threshold.
Challenges:
The process is complex (12+ processes), the yield is lower than HJT (currently about 95%, HJT reaches 97%+), and the production cost is high (20%-30% higher than PERC).
Scaling is difficult, the equipment is highly customized (such as lithography equipment relies on Germany's SUSS and Israel's Orbotech), and the production capacity is slow to climb.
Market Positioning And Application Scenarios
1. HJT's main battlefield
Distributed photovoltaics: household, industrial and commercial roofs (high bifaciality, beautiful, low attenuation).
High-end export market: Europe, the United States, Japan and other regions with high requirements for efficiency and appearance (such as California, Germany's household market).
Future direction: stacking technology (HJT + perovskite), targeting BIPV, automotive photovoltaics and other scenarios.
2. The main battlefield of BC
High-end distributed and high-end components: scenes with extremely high requirements for appearance (such as high-end residential and commercial buildings).
High-efficiency demand for centralized power stations: such as the Middle East, North Africa and other regions with sufficient sunlight, reducing the cost per kilowatt-hour through efficiency advantages.
Technology integration: TOPCon-BC (Longi HPBC) has become the current mainstream, taking into account efficiency and process compatibility.
Future Trends And Competitive Landscape
Short term (2025-2026):
HJT: Focus on breakthroughs in copper electroplating mass production and equipment localization (reducing costs). It is expected that the GW-level copper electroplating production line will be put into operation in 2025, and the cost will be close to TOPCon.
BC: Longi, Aixu and other leading companies are accelerating HPBC mass production (Longi HPBC production capacity will reach 15GW in 2024), focusing on high-end market premium.
Mid-term (2026-2030):
The two may move towards technological integration: such as HJT-BC stacking (combining heterojunction low-temperature process with back contact gridless design), or TOPCon-BC further optimizes costs.
Market share differentiation: HJT occupies the distributed and emerging markets with its compatibility and stacking potential, while BC leads in high-end and specific scenarios with its extreme efficiency.
Industry chain game:
HJT: Equipment vendors (Maxway, JEC) and material vendors (Dico, silver paste/copper electroplating) are the key.
BC: LONGi, Aiko and other vertically integrated manufacturers dominate, and equipment vendors need to break through bottlenecks such as lithography and masks.
Summary: How to choose?
Pursue extreme efficiency and appearance: BC (especially HPBC) is better, suitable for high-end markets and scenarios that are sensitive to aesthetics.
Taking into account efficiency, cost and future potential: HJT has more advantages, especially in stacking technology and thin-film cost reduction paths are clear.
The technical route is not a zero-sum game: the two complement each other in different scenarios, and may form new technologies such as "HJT-BC" through integration, jointly promoting breakthroughs in industry efficiency.