Micro-structured inverted pyramid texturization of Si inspired by self-assembled Cu nanoparticles

Abstract

A superior micron-sized inverted pyramid structure has been successfully achieved by one-step copper nanoparticles assisted chemical etching in Si/Cu(NO)/HF/HO solution for light trapping in silicon solar cells. The detailed mechanisms of such a novel method have been systematically demonstrated. The charge transfer during the reaction has been revealed by the simplified energy band diagram of the system as well. In order to form micro-structured inverted pyramids, the generation and dissolution of Cu nanoparticles should keep in balance during the reaction, which depends on the concentration of the etchant, the doping type and the doping level of the silicon substrate. With the investigation of the intrinsic properties of the silicon substrate, the etching rate is found out as a combined result of the electron concentration and the defect density of the substrate, as well as the potential barrier on the interface of Si/Cu nanoparticles. Furthermore, the anisotropic nature of Cu assisted chemical etching has also been investigated.

Difference in anisotropic etching characteristics of alkaline and copper based acid solutions for single-crystalline Si

“…More Cu nanoparticles nucleate on Si (100) plane because of the higher probability of Cu 2+ ions to capture electrons. Si underneath the Cu nanoparticles are preferentially oxidized and then etched by HF, leading to a faster etching along Si [100] directions 11 , 14 , 15 . Thus, both the lower reduction potential of Cu 2+ /Cu and different electronic properties of (100) and (111) planes in c-Si contribute to the anisotropic etching of CACE.…”

Minimization of Optical Reflectance by Copper Assisted Etching of Crystalline Silicon Surface

“…In the one step process, the growth Equation and the Cu oxidation Equation and etching of the resulting oxide by HF simultaneously occur on the surface. Accepting the idea of frequently reported MACE model about a localized microscopic galvanic cell that forms under the nanoparticle between the metal and silicon, we suppose that during the CuACE the Cu nanoparticles precipitate on the surface and an appearance of a nanoparticle immediate initiate the galvanic cell mechanism controlled etching.…”

“…As the MACE is obtained not only for the noble metal catalysts but also for cheaper metals like copper it is highly attractive to investigate the details of the Cu‐assisted process. It was suggested in Ref.…”

“…However, the understanding of the factors that are crucial for controlled texturing of the silicon surfaces by the copper‐assisted chemical etching is not yet sufficient for a practical application in the manufacturing of the devices. In addition, in spite of the commonly accepted fundamental mechanism for the MACE in silicon, there is still a lack of knowledge about how to use the key‐variables, namely etching time, metal catalyst type, etchant, and etc., for the intentional control of the processes aiming to produce the predictable and fully functional micro and nanostructures on the Si surfaces. There is still not clear how to control the texturing aiming to optimize the optical reflectance though some aspects of the relationship between the textured surfaces and the reflectance were described in Refs.…”

“…There is still not clear how to control the texturing aiming to optimize the optical reflectance though some aspects of the relationship between the textured surfaces and the reflectance were described in Refs. .…”