As the photovoltaic industry upgrades from P-type PERC to N-type, N-type TOPCon has become the mainstream global approach. Its high efficiency, low degradation, and outstanding bifacial gain have made it a core choice for large-scale power plants and industrial and commercial projects. Leading manufacturers (LONGi, JA Solar, Trina Solar,Luan Solar etc.) have fully entered the mass production stage of TOPCon, and efficiency breakthroughs in the industry continue to accelerate. 2025–2027 will be the period of widespread adoption of TOPCon.
To help industry professionals, project developers, and system designers better understand the technical landscape of TOPCon technology, we have compiled a comprehensive glossary covering core terminology across cell architecture, manufacturing processes, performance parameters, and application scenarios. This glossary serves as a practical reference for anyone seeking to deepen their understanding of TOPCon solar panels and the broader N-type ecosystem.
| Term | Definition |
| TOPCon (Tunnel Oxide Passivated Contact) | High-efficiency solar cell technology using ultra-thin oxide and polysilicon layers. |
| N-type Silicon | Phosphorus-doped silicon with high minority carrier lifetime and low degradation. |
| Tunnel Oxide Layer | Ultra-thin SiO₂ layer enabling selective carrier tunneling. |
| Polysilicon Layer | Polysilicon thin film enabling passivated contact and improved efficiency. |
| Passivated Contact | Structure that reduces interface recombination and increases Voc. |
| Selective Emitter | Emitter with varied doping concentration to improve conversion efficiency. |
| Bifaciality | Ratio of rear-side power to front-side power of a bifacial solar module. |
| Light-Induced Degradation (LID) | Power degradation caused by light exposure; minimal in N-type TOPCon. |
| LeTID | Light and elevated temperature-induced degradation; low in TOPCon modules. |
| Half-cut Cell | Cell-cutting technique reducing current loss and improving power output. |
| M10 Wafer | 182 mm silicon wafer standard widely used in TOPCon modules. |
| G12 Wafer | 210 mm wafer format for high-power modules. |
| POCl3 Diffusion | Phosphorus diffusion step in N-type solar cell processing. |
| LPCVD | Low-pressure chemical vapor deposition used for polysilicon layer deposition. |
| ALD | Atomic layer deposition enabling precise oxide layer control. |
| PECVD | Plasma-enhanced chemical vapor deposition for passivation layers. |
| Laser Contact Opening (LCO) | Laser process used to open contact holes accurately. |
| Screen Printing | Metal printing process forming electrodes using silver paste. |
| Bifacial Gain | Additional power generated from the rear side in bifacial modules. |
| Degradation Rate | Annual power degradation after the first year. |
| IEC 61215 | International standard for PV module performance testing. |
| IEC 61730 | Standard for PV module safety testing. |
| PAN File | Performance parameter file for PVsyst simulation. |
| Utility-scale Plant | Large-scale solar power plant installation. |
| BIPV | Building-integrated photovoltaic systems. |
| Tracker System | Solar tracking mounting system increasing yield. |
| LCOE | Levelized cost of electricity for solar power. |
| TOPCon solar cell | Tunnel Oxide Passivated Contact crystalline silicon solar cell that uses an ultra-thin tunnel oxide layer and a heavily doped polycrystalline silicon layer to achieve excellent surface passivation and high efficiency. |
| Tunnel Oxide Passivated Contact | Contact structure consisting of a ~1–2 nm ultra-thin SiO₂ tunnel layer and a heavily doped poly-Si layer, enabling strong surface passivation and carrier-selective transport with low contact resistance. |
| N-type silicon wafer | Crystalline silicon wafer doped with donor impurities (e.g., phosphorus). It offers high minority carrier lifetime and is free from conventional boron-related light-induced degradation, making it the mainstream substrate for TOPCon cells. |
| P-type silicon wafer | Crystalline silicon wafer doped with acceptor impurities (e.g., boron). It was the main substrate for PERC cells but suffers from light-induced degradation and is gradually being replaced by N-type wafers in high-efficiency technologies. |
| Crystalline silicon solar cell(c-Si solar cell) | Solar cell based on monocrystalline or multicrystalline silicon wafers. It accounts for the vast majority of the global PV market and includes technologies such as PERC, TOPCon, HJT, and IBC. |
| PERC solar cell | Passivated Emitter and Rear Cell technology using rear-side passivation layers and local contacts to improve efficiency compared with standard Al-BSF cells. Considered the previous mainstream before N-type TOPCon. |
| Heterojunction solar cell(HJT) | High-efficiency cell structure combining crystalline silicon wafers with thin amorphous silicon layers on both sides, offering excellent open-circuit voltage and temperature coefficient but requiring higher CAPEX and more complex processes. |
| Back-contact solar cell(IBC / TBC) | Solar cell with all positive and negative contacts located on the rear side (Interdigitated Back Contact) or using a tunnel-oxide back contact (TBC), enabling high efficiency and reduced front-side shading. |
| Ultra-thin silicon oxide layer(Ultra-thin SiO₂) | Thermally grown silicon dioxide layer with typical thickness of ~1–2 nm used as a tunnel oxide in TOPCon cells, providing excellent chemical passivation while allowing carrier tunneling. |
| Heavily doped polycrystalline silicon layer(Poly-Si layer) | Heavily doped polycrystalline silicon film deposited on top of the tunnel oxide, forming a strong electric field and selective contact for carriers in TOPCon structures. |
| Carrier-selective contact | Contact structure that allows only one type of carrier (electrons or holes) to pass easily while blocking the opposite type, significantly reducing recombination losses and improving Voc and fill factor. |
| Surface recombination | Recombination of charge carriers at material surfaces or interfaces due to defects or dangling bonds. Excessive surface recombination reduces cell efficiency; TOPCon aims to strongly suppress it. |
| Effective minority carrier lifetime | A key indicator of material quality and recombination in silicon. Longer minority carrier lifetime implies lower recombination losses and higher potential cell efficiency. |
| Open-circuit voltage(VOC) | Voltage across the cell terminals under illumination when the external circuit is open. It is strongly influenced by recombination losses; TOPCon cells can reach Voc values above 720 mV. |
| Short-circuit current density(Jsc) | Current density through the cell under illumination when the terminals are shorted. It reflects the light absorption and carrier collection capability of the device. |
| Fill factor | Ratio of the maximum obtainable power to the product of Voc and Jsc. It describes the 'squareness' of the I–V curve and is affected by series resistance, shunt resistance, and recombination. |
| Cell conversion efficiency | Ratio of electrical output power to incident light power for a single solar cell under standard test conditions (STC). Mass-produced TOPCon cells commonly reach 24–25% efficiency. |
| Module efficiency | Conversion efficiency measured at the PV module level, considering interconnection and encapsulation losses. High-power TOPCon modules can reach around 24% efficiency or higher. |
| Bifacial module | PV module capable of generating electricity from both the front and rear sides. TOPCon bifacial modules can achieve high bifaciality (rear-to-front power ratio), enhancing energy yield in suitable sites. |
| Temperature coefficient | Rate at which module power changes with cell temperature (usually %/°C). A smaller absolute value means better performance at high temperature; TOPCon modules typically have better temperature coefficients than PERC. |
| Light-Induced Degradation | Power degradation occurring when P-type boron-doped cells are exposed to light, mainly due to the activation of boron-oxygen complexes. N-type TOPCon cells are essentially free from conventional LID. |
| Light and elevated Temperature Induced Degradation | Degradation mechanism that occurs under combined light exposure and elevated temperatures. Proper process optimization and encapsulation can mitigate LeTID in PERC and N-type technologies. |
| Potential-Induced Degradation | Performance loss caused by high system voltage, humidity, and leakage currents through encapsulation materials. It can be mitigated by optimized module design, materials, and grounding schemes. |
| Series resistance | Equivalent series resistance in the solar cell or module, including bulk, contact, and interconnection resistances. High series resistance reduces fill factor and power output. |
| Back surface field | Highly doped region at the rear of conventional cells (e.g., Al-BSF structures) used to improve rear-side reflection and reduce recombination. In TOPCon, the back side is replaced by a tunnel oxide passivated contact. |
| Half-cut module | Module assembled from solar cells that have been cut into halves to reduce current, lower resistive losses, and improve shade tolerance and power output. |
| Module power rating | Nameplate power of a PV module at standard test conditions (STC), typically expressed in watts (W). High-power TOPCon modules can reach 600–700 W for large-format designs. |
| Balance of System cost | All system costs of a PV plant excluding the modules themselves, including mounting structures, cabling, inverters, land, and installation. Higher-efficiency modules help reduce BOS cost per watt. |
| Energy Payback Time(EPBT) | Time required for a PV system to generate the same amount of energy that was consumed in its production, transportation, and installation. |
| Levelized Cost of Energy(LCOE) | Key economic indicator that represents the average cost per kilowatt-hour of electricity generated over the lifetime of a power system, considering CAPEX, OPEX, and energy yield. High-efficiency, long-lifetime TOPCon modules help lower LCOE. |
With TOPCon now positioned as the central growth engine of the global PV industry, establishing a clear and standardized technical vocabulary is essential for enabling effective communication across R&D, manufacturing, EPC, and investment domains. We hope this industry glossary supports more informed decision-making and equips professionals with the knowledge needed to evaluate, compare, and apply TOPCon technology across diverse project environments. As the technology continues to evolve, we will update this glossary to ensure it remains aligned with the latest advancements and best practices.
