Key takeaways:
Cybrid evaluated the PID behavior of TOPCon modules with EVA and EPE films and highlighted the need for materials that perform well even before recovery
Raybo, the company’s down-conversion additive, was shown to improve UV stability and maintain output under UVID stress conditions
Comparative testing indicated stable long-term performance and higher quantum efficiency for Raybo-enhanced films relative to other down-conversion materials
At the TaiyangNews Cell & Module Production Equipment & Processing Materials conference, Hisanari Onouchi, Deputy CTO of Cybrid Technologies, discussed how encapsulants can be optimized to improve the performance and reliability of TOPCon modules.
Onouchi first compared PERC and TOPCon cell characteristics to frame the requirements for module materials. While PERC uses aluminum BSF and rear-side passivation on p-type wafers, TOPCon cells employ a thin tunnel oxide and doped polysilicon layer to improve carrier lifetime, temperature coefficient, and low-light performance. TOPCon also offers superior bifaciality and durability; however, it exhibits a unique vulnerability, UV-induced degradation (UVID), which is linked to the breakage of Si-H bonds in the passivation layers.
He then outlined Cybrid’s strategy for ‘better’ TOPCon modules, defined as those that deliver both high efficiency and reliable performance over time. For bifacial modules, he emphasized the importance of double-glass construction for mechanical stability, along with strong anti-PID performance even though TOPCon inherently fares better than p-type architectures. To counter UVID, Cybrid stated that encapsulants should incorporate both UV-cut and UV-down-conversion functionalities, absorbing harmful UV while re-emitting it as visible light usable by the cell.
Next, Onouchi reviewed the differences between common encapsulant types – EVA, POE, and EPE (EVA-POE-EVA stacked films). EVA is easy to process but can be prone to PID, while POE resists PID but tends to be stiffer and less transparent. EPE aims to combine the advantages of both and has gained traction in double-glass module designs, where lamination conditions become more challenging due to the heat capacity and rigidity of the glass sheets. Cybrid evaluated the PID resistance of TOPCon modules laminated with EVA and various EPE formulations under -1,500 V, 85°C, and 85% humidity for 192 hours, followed by outdoor light soaking. EVA showed poor recovery, while conventional EPE improved after soaking. However, some customers required materials that perform well even before recovery, leading Cybrid to further develop EPE films. Cybrid demonstrated PID results with its EPE product that showed lower PID (1.2% degradation) even without light-soaking recovery.
The latter half of the presentation focused on the UVID issue and Cybrid’s down-conversion additive, Raybo. Tests on several off-the-shelf TOPCon modules showed significant degradation under UV exposure, with none meeting IEC’s proposed limit of less than 1% degradation after 60 kWh of UV irradiation. Cybrid’s Raybo additive absorbs UV light and re-emits visible light, allowing modules to maintain output while blocking UV. Onouchi presented that the additive’s high quantum efficiency of >98% indicates no energy loss in down conversion, and that long-term durability of over 30 years was observed based on accelerated testing. Raybo-enhanced encapsulants demonstrated improved external quantum efficiency (EQE) and an estimated performance gain of about 1% compared with standard UV-cut materials. Outdoor monitoring of full-size modules installed in Osaka showed an annual energy gain of 2.5 kWh/m².
Durability testing indicated that Raybo’s UV-blocking and down-conversion properties remained stable under damp heat exposure. Cybrid also compared Raybo with other down-conversion additives available on the market and reported superior IV stability, and a quantum efficiency of 98% compared with 91% and 87% from other competitors. According to Onouchi, Raybo has been used in heterojunction modules from CIC since 2015 and continues to show stable outdoor performance. When Raybo films were applied to commercially purchased TOPCon modules for UVID testing, all modules – including those with high initial degradation - showed no UV-induced losses. Onouchi concluded by stating that Raybo-based EPE films are now being adopted in double-glass TOPCon modules as a practical pathway to suppress UVID while maintaining high efficiency.