Nanomaterials 2021, 11, 2581. https://doi.org/10.3390/nano11102581 www.mdpi.com/journal/nanomaterials Article Simple Self‐Assembly Strategy of Nanospheres on 3D Substrate and Its Application for Enhanced Textured Silicon Solar Cell Dan Su 1,† , Lei Lv 2,† , Yi Yang 2 , Huan‐Li Zhou 2 , Sami Iqbal 2 and Tong Zhang 1,2,3, * 1 Key Laboratory of Micro‐Inertial Instrument and Advanced Navigation Technology, Ministry of Education, School of Instrument Science and Engineering, Southeast University, Nanjing 210096, China; jssysls@163.com 2 Joint International Research Laboratory of Information Display and Visualization, School of Electronic Science and Engineering, Southeast University, Nanjing 210096, China; lvlei@seu.edu.cn (L.L.); yyang19x@163.com (Y.Y.); huanli_zhou@163.com (H.‐L.Z.); 101300112@seu.edu.cn (S.I.) 3 Suzhou Key Laboratory of Metal Nano‐Optoelectronic Technology, Southeast University Suzhou Campus, Suzhou 215123, China * Correspondence: tzhang@seu.edu.cn † Equally contributed. Abstract: Nanomaterials and nanostructures provide new opportunities to achieve high‐perfor‐ mance optical and optoelectronic devices. Three‐dimensional (3D) surfaces commonly exist in those devices (such as light‐trapping structures or intrinsic grains), and here, we propose requests for nanoscale control over nanostructures on 3D substrates. In this paper, a simple self‐assembly strat‐ egy of nanospheres for 3D substrates is demonstrated, featuring controllable density (from sparse to close‐packed) and controllable layer (from a monolayer to multi‐layers). Taking the assembly of wavelength‐scale SiO2 nanospheres as an example, it has been found that textured 3D substrate promotes close‐packed SiO2 spheres compared to the planar substrate. Distribution density and lay‐ ers of SiO2 coating can be well controlled by tuning the assembly time and repeating the assembly process. With such a versatile strategy, the enhancement effects of SiO2 coating on textured silicon solar cells were systematically examined by varying assembly conditions. It was found that the close‐packed SiO2 monolayer yielded a maximum relative efficiency enhancement of 9.35%. Com‐ bining simulation and macro/micro optical measurements, we attributed the enhancement to the nanosphere‐induced concentration and anti‐reflection of incident light. The proposed self‐assembly strategy provides a facile and cost‐effective approach for engineering nanomaterials at 3D inter‐ faces. Keywords: self‐assembly; 3D substrate; solar cell 1. Introduction The development of nanomaterials and nanostructures provides new opportunities for performance boosting of optical and optoelectronic devices [1–5]. For example, dielec‐ tric nanostructures are used to enhance the transmission and brightness of different trans‐ parent windows or display screens [6–9], and plasmonic or dielectric nanocoatings are widely proposed and applied to enhance the efficiency of photovoltaic devices or sensi‐ tivity of photodetectors [1,10]. In many optoelectronic devices, there are complex 3D sur‐ faces [11,12]. For example, micron and nanoscale heterogeneities exist in various photo‐ voltaic devices [13], such as the intrinsic grains in polycrystalline solar cells [14–16] and textured surfaces in the commercial silicon solar cells for light‐trapping [17]. In this context, there has been a drive for designing and fabricating nanostructures on 3D surfaces with desired control. On planar substrates or interfaces, both top‐down Citation: Su, D.; Lv, L.; Yang, Y.; Zhou, H.‐L.; Iqbal, S.; Zhang, T. Simple Self‐Assembly Strategy of Nanospheres on 3D Substrate and Its Application for Enhanced Textured Silicon Solar Cell. Nanomaterials 2021, 11, 2581. https://doi.org/10.3390/nano11102581 Academic Editors: Jihoon Lee and Ming‐Yu Li Received: 10 August 2021 Accepted: 27 September 2021 Published: 30 September 2021 Publisher’s Note: MDPI stays neu‐ tral with regard to jurisdictional claims in published maps and insti‐ tutional affiliations. Copyright: © 2021 by the authors. Li‐ censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con‐ ditions of the Creative Commons At‐ tribution (CC BY) license (http://crea‐ tivecommons.org/licenses/by/4.0/).