Guthrey Harvey, Lima Anderson Caroline, Kale Abhijit S, Nemeth William, Page Matthew, Agarwal Sumit, Young David L, Al-Jassim Mowafak, Stradins Paul
National Renewable Energy Laboratory, Golden, Colorado 80401, United States.
Colorado School of Mines, Golden, Colorado 80401, United States.
ACS Appl Mater Interfaces. 2020 Dec 16;12(50):55737-55745. doi: 10.1021/acsami.0c12795. Epub 2020 Dec 1.
High-efficiency silicon solar cells rely on some form of passivating contact structure to reduce recombination losses at the crystalline silicon surface and losses at the metal/Si contact interface. One such structure is polycrystalline silicon (poly-Si) on oxide, where heavily doped poly-Si is deposited on a SiO layer grown directly on the crystalline silicon (c-Si) wafer. Depending on the thickness of the SiO layer, the charge carriers can cross this layer by tunneling (<2 nm SiO thickness) or by direct conduction through disruptions in the SiO, often referred to as pinholes, in thicker SiO layers (>2 nm). In this work, we study structures with tunneling- or pinhole-like SiO contacts grown on pyramidally textured c-Si wafers and expose variations in the SiO layer properties related to surface morphology using electron-beam-induced current (EBIC) imaging. Using EBIC, we identify and mark regions with potential pinholes in the SiO layer. We further perform high-resolution transmission electron microscopy on the same areas, thus allowing us to directly correlate locally enhanced carrier collection with variations in the structure of the SiO layer. Our results show that the pinholes in the SiO layer preferentially form in different locations based on the annealing conditions used to form the device. With greater understanding of these processes and by controlling the surface texture geometry, there is potential to control the size and spatial distribution of oxide disruptions in silicon solar cells with poly-Si on oxide-type contacts; usually, this is a random phenomenon on polished or planar surfaces. Such control will enable us to consistently produce high-efficiency devices with low recombination currents and low junction resistances using this contact structure.
高效硅太阳能电池依赖于某种形式的钝化接触结构，以减少晶体硅表面的复合损失以及金属/硅接触界面处的损失。一种这样的结构是氧化物上的多晶硅（poly-Si），其中重掺杂的多晶硅沉积在直接生长在晶体硅（c-Si）晶圆上的SiO层上。根据SiO层的厚度，电荷载流子可以通过隧穿（SiO厚度<2 nm）穿过该层，或者在较厚的SiO层（>2 nm）中通过SiO中的缺陷（通常称为针孔）进行直接传导穿过该层。在这项工作中，我们研究了在金字塔形纹理的c-Si晶圆上生长的具有隧穿或针孔状SiO接触的结构，并使用电子束诱导电流（EBIC）成像揭示了与表面形态相关的SiO层特性的变化。使用EBIC，我们识别并标记了SiO层中可能存在针孔的区域。我们进一步对相同区域进行了高分辨率透射电子显微镜检查，从而使我们能够将局部增强的载流子收集与SiO层结构的变化直接关联起来。我们的结果表明，基于用于形成器件的退火条件，SiO层中的针孔优先在不同位置形成。通过对这些过程有更深入的了解并控制表面纹理几何形状，有可能控制具有氧化物上多晶硅型接触的硅太阳能电池中氧化物缺陷的尺寸和空间分布；通常，这在抛光或平面表面上是一种随机现象。这种控制将使我们能够使用这种接触结构持续生产具有低复合电流和低结电阻的高效器件。
