In this article, detailed numerical modeling is performed for front junction (FJ) and rear junction (RJ) n-type Si solar cells with screen-printed double-side poly-Si based tunnel oxide passivated contacts (TOPCon). A roadmap for efficiency projections of commercial-type RJ and FJ topologies reaching 24.8% and 23.3% efficiencies, respectively, has been developed to quantify and explain the impact of various technological innovations on the performance of each design. Understanding of mechanisms governing cell operation is crucial to explore factors that limit the efficiency potential of the two device structures. By investigating several key parameters such as front poly-Si sheet resistance and thickness, bulk material properties, and current transport in our simulation model, we determine and explain why RJ cells outperform FJ cells. Our findings reveal that FJ suffers from present technological limitations of p-type poly-Si based passivated contacts—namely, 1) large recombination observed in textured p-TOPCon layers and 2) low boron solid solubility and hole mobility in boron-doped poly-Si which results in very high sheet resistance of the front p-poly-Si emitter that contributes to fill factor degradation, especially when using thin poly-Si layer to reduce absorption losses. RJ on the contrary desensitizes the cell efficiency to front sheet resistance to allow the application of ultra-thin front n-type poly-Si layer and is therefore ideally suited for double-side TOPCon cells.

中文翻译：

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前后结双面钝化接触太阳能电池的设计、优化及深入了解

在本文中，对具有丝网印刷双面多晶硅基隧道氧化物钝化触点 (TOPCon) 的前结 (FJ) 和后结 (RJ) n 型硅太阳能电池进行了详细的数值建模。商业型 RJ 和 FJ 拓扑的效率预测路线图分别达到 24.8% 和 23.3% 的效率，以量化和解释各种技术创新对每种设计性能的影响。了解控制单元操作的机制对于探索限制两种器件结构效率潜力的因素至关重要。通过研究模拟模型中的几个关键参数，例如正面多晶硅薄层电阻和厚度、体材料特性和电流传输，我们确定并解释了为什么 RJ 电池优于 FJ 电池。我们的研究结果表明，FJ 受到基于 p 型多晶硅钝化触点的当前技术限制——即，1）在有纹理的 p-TOPCon 层中观察到大量复合和 2）在掺硼多晶硅中硼固体溶解度和空穴迁移率低。 Si 导致前 p-poly-Si 发射器的方块电阻非常高，这会导致填充因子下降，尤其是在使用薄多晶硅层来减少吸收损耗时。相反，RJ 使电池效率对前表面电阻不敏感，以允许应用超薄前 n 型多晶硅层，因此非常适合双面 TOPCon 电池。1) 在带纹理的 p-TOPCon 层中观察到大量复合，2) 在掺硼多晶硅中硼固溶度和空穴迁移率低，这导致前 p-多晶硅发射极的方块电阻非常高，从而导致填充因子退化，尤其是在使用薄多晶硅层以减少吸收损耗时。相反，RJ 使电池效率对前表面电阻不敏感，以允许应用超薄前 n 型多晶硅层，因此非常适合双面 TOPCon 电池。1) 在带纹理的 p-TOPCon 层中观察到大量复合，2) 在掺硼多晶硅中硼固溶度和空穴迁移率低，这导致前 p-多晶硅发射极的方块电阻非常高，从而导致填充因子退化，尤其是在使用薄多晶硅层以减少吸收损耗时。相反，RJ 使电池效率对前表面电阻不敏感，以允许应用超薄前 n 型多晶硅层，因此非常适合双面 TOPCon 电池。