Complementary etching behavior of alkali, metal‐catalyzed chemical, and post‐etching of multicrystalline silicon wafers

Abstract

Both alkali and metal-catalyzed chemical etching (MCCE) of multicrystalline silicon (mc-Si) wafer show anisotropic etching behavior, resulting in different morphologies among the different grains. However, by combining alkali etching, MCCE, and a post-etching process, homogeneous microstructures can be obtained on the surface of mc-Si wafer. After the first alkali etching, there are three typical morphologies of upward pyramids, terraces, and tilt planes, and relative to the initial Si(100), Si(110), and Si(111) dominated grains, these show low, moderate, and high reflection, respectively. After MCCE and the post-etching process, the microstructures on the different grains have converged to a similar morphology and reflection. Mc-Si solar cells fabricated by complementary alkali etching, MCCE, and post-etching have a good appearance and high efficiency of~19.4%. Moreover, the cells with submicrometer texture have the advantages of reverse current-voltage characteristics and weak light response over traditional cells with micrometer texture. KEYWORDS alkali etching, complementary etching behavior, metal-catalyzed chemical etching, multicrystalline silicon solar cell, power conversion efficiency

On the Enhanced Phosphorus Doping of Nanotextured Black Silicon

“…Different MCCE texture conditions (MCCE-1 to MCCE-3) were achieved by varying the post-nanopitting etch time, with MCCE-1 corresponding to the longest etch time and MCCE-3 to the shortest. More processing details are available in [9]. RIE B-Si textures were prepared with a noncryogenic RIE process using a SPTS Pegasus system with a temperature of −20°C, SF 6 and O 2 plasma with a 7:10 gas flow ratio, a total chamber pressure of 38 mTorr, 3000 W coil power, and 10 W platen power.…”

“…, microstructures with tapered conical spikes [3]- [5], high aspect ratio nanoscale needles, vertical pores, or columns [6], inverted submicron structures [7]- [9], and highly ordered arrays of nanorods, cones [10], and pencils [10]- [12], as well as micropillars and micropencils [13]. B-Si nanotextures are of particular interest for photovoltaic applications because of their low reflectance and enhanced optical absorption, which could enable higher solar cell efficiencies.…”

“…B-Si nanotextures are of particular interest for photovoltaic applications because of their low reflectance and enhanced optical absorption, which could enable higher solar cell efficiencies. B-Si texturing processing incorporating metal-assisted chemical etching (MACE) or metal-catalyzed chemical etch (MCCE) with subsequent alkaline or acidic etching have already been adopted for industrial multicrystalline solar cells [9], [14]. However, there are challenges with integrating B-Si into solar cells including increased surface recombination associated with its increased surface area and the increased Auger recombination associated with its enhanced doping effect [15].…”

Silicon Nanotexture Surface Area Mapping Using Ultraviolet Reflectance

“…The MCCE texture process employed an initial damage removal step followed by an AgNO 3 solution nano-pitting step and a subsequent HF-HNO 3 step to create inverted texture features. More processing details are available in [31]. The two MCCE conditions were created by varying the post-nano-pitting etch time, with MCCE-1 corresponding to the longer etch time and MCCE-2 to the shorter.…”

Texturing Technology on Multicrystalline Silicon Wafer by Metal-catalyzed Chemical Etching: a Review

“…图 5 (a)纳米绒面、(b)微米绒面及(c)纳米-微米复合绒面 SEM 表面形貌照片 [31] Fig. 5 SEM images of silicon surfaces of (a) nano-texture, (b) micro-texture and (c) nano-micro-texture [31] 金刚线切割多晶硅片的表面有损伤层存在，因 此在 MCCE 法制绒前需要将损伤层去除。Wu 等 [33] 提出了一种引入人工缺陷然后在金刚线切割多晶硅 片表面制绒的方法。该方法无需去除损伤层，直接 将切割后的多晶硅片浸入到 HF/HNO3/AgNO3 溶液 中，硅片表面就会引入大量的人工缺陷。HF/HNO3 溶液可以将纳米级的绒面腐蚀扩展为亚微米级的绒 面， 过程示意图见图 6(a)。 通过该方法获得的绒面， 形貌示意图和反射率曲线如图 6(b)所示，反射率约 为 19%，远低于传统的 HF/HNO3 制绒体系。太阳能 电池的光电转换效率可以达到 19.07%。该方法简单 易行，通过改进光学抗反射和表面钝化，最终提高 了电池片的光电转换效率。 碱和 MCCE 腐蚀的多晶硅均出现了各向异性 腐蚀现象，Zou 等 [34] 结合碱腐蚀、Ag-MCCE 以及后 腐蚀处理工艺，可以在多晶硅片表面消除各向异性 腐蚀，获得均匀的绒面结构。第一次碱腐蚀后，在 初始的 Si(100)、 (110)和(111)晶面上分别出现了倒金 字塔、阶梯以及倾斜面三种形貌。再经过 Ag-MCCE 和后腐蚀处理，不同晶粒上的微观结构可以调整为 结构相似、反射率相近的形貌(图 7) 。通过上述工 艺制备的太阳能电池片具有良好的外观和约 19.4% 的光电转换效率。此外，该方法获得的亚微米绒面 的太阳能电池具有优良的电流-电压特性以及弱光 响应等性能。 图 6 (a)DWS 多晶硅片表面制备亚微米级(SIM)绒面的过程示意图和(b)三种绒面结构的反射率结果 [33] Fig. 6 (a) Schematic illustration of the main steps to prepare the submicron-in-micron(SIM) texture on the DWS mc-Si wafer and (b) experimental reflectance (curves) and simulated reflectance (scatter points) of three samples [33] 图 7 碱、Ag-MCCE 和后腐蚀处理获得的不同晶面的硅片表 面和截面 SEM 照片 [34] Fig .7 Surface and cross-sectional SEM images of mc-Si grains after etching by alkali, Ag-MCCE and post-etching with different orientations [34] (a [37] 。铜膜阻碍了腐蚀 液与硅表面的进一步接触，使反应停滞，无法在硅 片表面获得绒面结构。因此，往往在 Cu-MCCE 过 程中加入氧化剂，例如 H2O2 或 FeCl3 等，持续氧化 Cu，以确保腐蚀反应持续进行 [38] 。 在传统的酸腐蚀基础上，有文献进行了酸腐蚀 和铜催化腐蚀的复合制绒研究。Zou 等 [39] 采用酸性 湿法刻蚀预处理工艺，结合低成本的 Cu-MCCE 过 程成功实现了金刚线切割多晶硅片的表面制绒，获 得结构均匀的倒金字塔绒面。为了研究不同铜源对 制绒过程的影响，Sheng 等 [40] 分别选用了 CuSO4、…”