Potential-induced degradation (PID) may be a serious concern in photovoltaic (PV) modules and plants, particularly when approaching high system voltages (1500+ V). Here, we investigate PID occurring in bifacial rear-emitter silicon heterojunction (SHJ) solar cells encapsulated in a glass/glass (G/G) module configuration with ethylene vinyl acetate (EVA) as an encapsulant. PID testing was performed at 85°C in 85% relative humidity (RH), and the solar cells were subjected to −1 kV and +1 kV for up to 800 h. SHJ cells were found to degrade when subjected to −1 kV, and to a lesser extent when left unbiased in damp heat (DH) conditions, while the application of +1 kV prevented degradation. Although prone to PID after extended test durations, the SHJ mini-modules investigated in this study noticeably passed the industry standard (IEC 61215:2021) PID test of 96 h. The degradation was primarily characterized by losses in short-circuit current (I_SC) at the front side, followed by fill factor (FF) and open-circuit voltage (V_OC). A cross-sectional transmission electronic microscopy analysis of the laminates subjected to −1 kV highlighted a transport of sodium (Na) through the transparent conductive oxide (TCO), reaching the amorphous Si/TCO interface. The samples tested in DH conditions and with positive PID test conditions did not exhibit such a migration of Na. To account for these observations, we updated a previously proposed model describing the sensitivity of SHJ cells to water. In our degradation model, moisture in the module corrodes the glass, creating sodium hydroxide (NaOH) that then percolate through the EVA before reaching the SHJ cell. The application of a high negative bias amplifies the previous mechanism by increasing the availability of Na⁺ and also enhances the drift of Na⁺ through the EVA to the cell. Finally, we demonstrate that PID can be mitigated or suppressed at the module level by using a high-volume resistivity encapsulant with a low water vapor transmission rate (WVTR) or by encapsulating SHJ solar cells in a configuration impermeable to water (e.g., using an edge sealant).

中文翻译：

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双面硅异质结太阳能组件的电势诱导退化：见解和缓解策略

电势诱导退化 (PID) 可能是光伏 (PV) 模块和发电厂中的一个严重问题，特别是在接近高系统电压 (1500+ V) 时。在这里，我们研究了双面后发射极硅异质结 (SHJ) 太阳能电池中发生的 PID，该太阳能电池封装在玻璃/玻璃 (G/G) 模块配置中，并以乙烯醋酸乙烯酯 (EVA) 作为封装剂。 PID 测试在 85°C、85% 相对湿度 (RH) 下进行，太阳能电池承受 -1 kV 和 +1 kV 长达 800 小时。研究发现，SHJ 细胞在受到 -1 kV 电压时会发生降解，在湿热 (DH) 条件下不加偏压时降解程度较小，而施加 +1 kV 则可防止降解。尽管在延长测试持续时间后容易出现 PID，但本研究中研究的 SHJ 微型模块明显通过了 96 小时的行业标准 (IEC 61215:2021) PID 测试。退化的主要特征是正面的短路电流 (ISC _{)损失，其次是填充因子 (FF) 和开路电压 ( VOC} )。对经受 -1 kV 电压的层压板进行横截面透射电子显微镜分析，结果显示钠 (Na) 通过透明导电氧化物 (TCO) 传输，到达非晶 Si/TCO 界面。在 DH 条件和正 PID 测试条件下测试的样品没有表现出这样的 Na 迁移。为了解释这些观察结果，我们更新了之前提出的描述 SHJ 细胞对水敏感性的模型。在我们的降解模型中，模块中的湿气会腐蚀玻璃，产生氢氧化钠 (NaOH)，然后渗入 EVA，然后到达 SHJ 电池。高负偏压的应用通过增加Na ^{+的可用性而放大了先前的机制，并且还增强了Na +}通过EVA到达电池的漂移。最后，我们证明，通过使用具有低水蒸气透过率 (WVTR) 的高体积电阻率封装剂或通过将 SHJ 太阳能电池封装在不透水的配置中（例如，使用边缘密封剂）。