Key takeaways:
JTPV proposes solutions to UVID in high-efficiency n-type cells, which can be reduced by modifying front passivation and hydrogen management
Damp heat and PID mitigation depend heavily on metallization chemistry, dielectric integrity, and process control, while module-level materials such as encapsulants and glass further influence the outcomes
Advanced ARC stack, cut-edge treatments aim to improve long-term stability as modules adopt increasingly multi-cut formats
At the TaiyangNews Reliable PV Module Design 2025 Conference, Xinrui An, R&D Manager at Jietai Solar (JTPV), approached module reliability from a cell manufacturer’s perspective. Instead of focusing on module design, he walked through the main degradation mechanisms that affect today’s n-type modules. These are UV-induced degradation (UVID), damp heat (DH), and potential-induced degradation (PID). He explained how these can be addressed at the cell level.
UV-Induced Degradation
UVID has been widely discussed since 2023, particularly in relation to high-efficiency technologies such as TOPCon, heterojunction (HJT), and back-contact (BC) cells. The basic idea is that high-energy UV photons can break silicon-hydrogen bonds at the front surface of the cell. Given that modern high-efficiency cells rely heavily on dielectric passivation layers, they can be more sensitive to this effect. The primary electrical impact shows up in open-circuit voltage (Voc).
Early reports suggested very high degradation rates, sometimes above 10% relative. However, it has since become clear that part of this effect is linked to dark storage after UV exposure. If modules are measured after UV stress but before proper light stabilization, the loss can appear exaggerated. After light soaking, the actual UV degradation of many TOPCon modules typically ranges from 2-3%, which is still a significant challenge.
From a cell-level perspective, Xinrui explained that reducing UVID involves modifying the front-passivation scheme. At JTPV, this meant reducing dependence on hydrogen passivation and lowering overall UV absorption at the front surface. Technically, this can involve adjusting the aluminum oxide layer or tailoring the silicon nitride stack. However, this slightly reduced the Voc and short-circuit current (Isc), resulting in an absolute efficiency loss of about 0.1%. However, UV60 degradation with these adjustments has decreased from above 2% to around 1%.
Importantly, JTPV performed reliability testing without UV-blocking encapsulants or special BOM optimizations, since a cell supplier cannot control the final module bill of materials. Module makers, however, could further reduce UVID by using UV-cutoff or downshifting films if desired.
Damp Heat
Damp heat remains a classic yet critical reliability test that simulates conditions with high temperature and humidity. The main issue under DH is corrosion driven by acetic acid released from EVA encapsulants. This can attack cell metallization, increase series resistance, and create visible degradation patterns in electroluminescence (EL) images.
Xinrui described 3 typical failure patterns observed after DH stress:
Localized point failures, often linked to contaminants
Degradation around ribbon interconnection areas
Surface-wide degradation unrelated to contacts, possibly linked to encapsulant chemistry
At the cell level, one of the most effective mitigation measures is optimizing the silver paste composition. Reducing the aluminum content and reactive components in the paste lowers the risk of chemical reaction under humid conditions. Firing conditions must also be carefully aligned with paste chemistry to avoid residual reactive materials. Additionally, ensuring stable and blister-free anti-reflection coatings helps prevent these corrosive reactions.
From the module side, he noted that double-glass constructions generally perform better than single-glass modules under DH. Using POE instead of EVA also improves resistance, not only for DH but also for PID.
Potential-Induced Degradation
PID arises from the voltage differences between cells and the grounded module frame. The PID can be categorized into 3 types:
Polarization-type PID (PID-p) – this is caused by charge accumulation at the passivated interfaces, which leads to reduced Voc or Jsc. This is often reversible and can occur at relatively low-bias voltages.
Sodium-related shunting (PID-s) – in this type, Na ions migrate from glass through encapsulation layers under negative bias and create shunt paths in the emitter, which reduces fill factor. This is typically recoverable by applying an opposite bias or heat.
Corrosion-type PID (PID-c) – this is the severe stage of PID corrosion that involves chemical reactions between sodium precipitates and the dielectric layers, resulting in the degradation of passivation and possibly the p-n junction. This effect can be accelerated by moisture ingress.
For TOPCon, polarization-type PID is usually the primary concern. There are several countermeasures at the cell level to improve front dielectric conductivity: introducing thin interlayers to reduce potential differences and maintaining high film integrity to prevent ARC blistering or contamination. Aluminum oxide layers can also assist charge dissipation.
At the module level, sodium-free glass, higher-resistance encapsulants, moisture barriers, proper grounding, and anti-PID inverters all contribute to mitigation.
An also shared results from an outdoor comparison test conducted in northwestern China, using identical module BOMs but different cell suppliers. Two module strings were monitored, one using JTPV cells and another using cells from a tier-1 competitor, starting in December 2024.
After several months of operation, the JTPV-based modules showed slightly higher generation per watt and lower measured degradation. The seasonal variation in performance was linked to differences in temperature coefficients and Voc optimization strategies. In this case, JTPV had deliberately accepted a slightly lower Voc in exchange for better long-term UV and DH robustness.
An emphasized that reliability is not only about materials but also about process stability and cell architecture. For example:
Uniform rear-side deposition improves electrical stability.
Gradient-index anti-reflection coatings help balance hydrogen content and optical performance.
Optimized metallization reduces corrosion risk and improves current distribution.
Multi-busbar designs enhance mechanical strength and reduce localized heating.
He also introduced the half-cut edge passivation (HEP) concept and a newer cut line technology (CLT). The idea behind CLT is to locally remove the emitter along intended cutting lines before laser separation, reducing recombination damage at cut edges. The treated edges are then properly passivated. This helps improve fill factor and module power, especially as modules move toward quarter-cut or multi-split designs. Unlike fixed half-cut edge passivation schemes, CLT can be adapted more flexibly to different cell formats.
Xinrui An’s full presentation, titled Bringing Reliability & Efficiency to PV modules, can be accessed here.