TOPCon modules face 3 dominant reliability risks: damp-heat corrosion, PID, and UVID
Encapsulation architecture, paste selection, and backsheet choice strongly influence long-term TOPCon module stability
UV management through cut-off or down-conversion approaches is emerging as a critical design consideration for n-type modules
As TOPCon technology becomes the dominant cell architecture in the global PV market, module reliability is increasingly shaped by the interaction between advanced cell designs and encapsulation materials. Higher efficiencies, thinner wafers, and evolving metallization schemes are placing greater stress on encapsulation systems that must protect modules from electrical, chemical, and environmental degradation over multi-decade lifetimes.
Speaking at the TaiyangNews Virtual Conference on Reliable PV Module Design, Bo Jin, Overseas Sales Manager at HANGZHOU FIRST, addressed these challenges. The presentation, titled "High-Quality Encapsulation Solutions for High-Efficiency TOPCon PV Modules", focused on how encapsulation design affects the long-term reliability of high-efficiency TOPCon modules.
According to Jin, TOPCon module reliability risks can be grouped into 3 dominant failure modes: damp-heat-induced corrosion, potential-induced degradation (PID), and UV-induced degradation (UVID).
Damp-heat corrosion and PID were discussed as closely linked phenomena, since moisture ingress and ionic migration can simultaneously intensify corrosion reactions and leakage-current-driven degradation. UVID is increasingly being recognized as a growing concern for n-type architectures, where extended UV exposure can compromise the stability of TOPCon passivation layers over time (see Damp Heat Testing Reveals New Failure Mode In TOPCon Modules).
For glass-glass (G2G) TOPCon modules, Jin identified POE or EPE as the preferred front-side encapsulants for high-reliability designs. Under PID testing at 85°C, 85% RH, and –1,500 V, modules using POE- or EPE-based stacks showed power losses below 2% after 288 hours, with no requirement for UV recovery.
As a cost-effective alternative, Jin stated that anti-acid EVA (S406P) on both sides can also deliver acceptable PID performance, keeping residual losses below 3% after combined PID and UV exposure.
Damp-heat testing further highlighted encapsulant effects. After up to 3,000 hours of damp-heat exposure, G2G modules encapsulated with POE or EPE maintained power losses below 5%, while EVA-based stacks degraded earlier, typically after 1,500 hours. Anti-acid EVA again showed improved corrosion resistance compared with normal EVA. The company attributes damp-heat degradation primarily to paste corrosion caused by moisture ingress, which is exacerbated by acidic byproducts released from EVA and certain additives.
To reinforce this point, Jin compared TOPCon modules fabricated with different silver paste formulations under identical encapsulation. Even with the same EVA encapsulant, corrosion behavior varied significantly across pastes, demonstrating that metallization paste selection has a decisive impact on corrosion resistance and must be evaluated together with encapsulation materials.
For glass-backsheet (G2B) TOPCon modules, FIRST showcased its TF4N POE encapsulant on the front side as a high-reliability solution. This encapsulant combines a low water-vapor transmission rate with electrochemical reaction blocking, improving resistance to moisture-driven corrosion. On the rear side, white EVA or low-acid EVA can be used with a standard backsheet.
PID testing showed that both TF4N-based and EP-based front encapsulation stacks maintained power loss below 3% after 192 hours. Under damp-heat conditions, however, differences became more pronounced. G2B modules using TF4N on the front side maintained power losses below 5% even after 3,000 hours, while alternative front-side materials showed higher degradation after extended exposure.
Jin also highlighted the influence of cell selection. When different TOPCon cell types were tested under identical encapsulation and backsheet configurations, corrosion resistance varied significantly, underscoring that cell-level robustness remains critical, particularly for glass-backsheet module designs.
Backsheet choice produced some unexpected results. Standard polymer backsheets outperformed certain low-WVTR polymer designs during damp-heat testing. Jin explained that while low-WVTR backsheets limit external moisture ingress, they can also trap internally generated moisture and acidic species. For applications requiring extreme moisture control, the company recommends aluminum-foil backsheets, which eliminate both ingress and accumulation effects.
Jin explained that TOPCon cells are susceptible to UV-related degradation, despite performing well against BO-LID and LeTID. Prolonged UV exposure can degrade n-type passivation layers, making front-side UV management increasingly important.
FIRST presented 2 encapsulation-based mitigation approaches: UV cut-off films and UV down-conversion films. A 320 nm UV cut-off film was shown to provide an effective balance between protection and performance. While standard cut-off films can significantly reduce module power, the 320 nm design limited initial power loss to around 2 W on a 580 W TOPCon module, while keeping UVID-related power loss below 1% after UV60. The film maintained visible-light transmittance above 90% and showed good resistance to discoloration under both UV and damp-heat aging.
In the second approach, UV down-conversion is used to transform absorbed ultraviolet photons into visible light. FIRST’s films absorb UV radiation across the 320-380 nm range and re-emit it in the visible spectrum, with a peak around 425 nm. Testing demonstrated that the films could block almost all harmful UV radiation while keeping initial power losses below 1 W and limiting degradation to less than 1% after UV60 testing.
As a conclusion, Jin summarized FIRST’s recommendations. For glass-glass TOPCon modules, POE or EPE on the front side offers the highest reliability, while anti-acid EVA on both sides provides a cost-effective alternative. For glass-backsheet TOPCon modules, FIRST recommends TF4N POE on the front side combined with low-acid EVA and a standard backsheet; aluminum-foil backsheets are preferred where moisture control is critical. To mitigate UVID risks, either UV cut-off or UV down-conversion films can be applied to the front side.
The full presentation is available on the TaiyangNews YouTube channel here.
The TaiyangNews Solar Technology Conference India 2026 is taking place on February 5–6 at Aerocity, New Delhi. Spot registrations are open at the venue.