Fabrication and Doping Methods for Silicon Nano‐ and Micropillar Arrays for Solar‐Cell Applications: A Review

Abstract

Silicon is one of the main components of commercial solar cells and is used in many other solar-light-harvesting devices. The overall efficiency of these devices can be increased by the use of structured surfaces that contain nanometer- to micrometer-sized pillars with radial p/n junctions. High densities of such structures greatly enhance the light-absorbing properties of the device, whereas the 3D p/n junction geometry shortens the diffusion length of minority carriers and diminishes recombination. Due to the vast silicon nano- and microfabrication toolbox that exists nowadays, many versatile methods for the preparation of such highly structured samples are available. Furthermore, the formation of p/n junctions on structured surfaces is possible by a variety of doping techniques, in large part transferred from microelectronic circuit technology. The right choice of doping method, to achieve good control of junction depth and doping level, can contribute to an improvement of the overall efficiency that can be obtained in devices for energy applications. A review of the state-of-the-art of the fabrication and doping of silicon micro and nanopillars is presented here, as well as of the analysis of the properties and geometry of thus-formed 3D-structured p/n junctions.

Chemical approaches for doping nanodevice architectures

“…An in-depth study of the MLD process with regard to solar cell applications is outside the scope of this review, and the reader is directed to excellent reviews by Caccamo [29] and Elbersen. [30] Ye and co-workers further fine-tuned the MLD process through use of mixed-monolayers [31].…”

Photo‐Electrical Characterization of Silicon Micropillar Arrays with Radial p/n Junctions Containing Passivation and Anti‐Reflection Coatings

“…[11] Previously we showed the feasibility of radially doped silicon micropillars of 40 µm in length, with efficiencies well above 5%. [6][7][8] Yu et al have simulated the effect of surface passivation on nanopillar solar cells. [13] Their results suggest that surface passivation and p/n junction placement are important factors in the design of nanowire solar cells.…”

“…Silicon nano/micro-engineering process flows have enabled the fabrication of more complex structured silicon solar cells, and in particular the development of 3D micropillar structures with radial p/n junctions. [5][6][7][8] The efficiencies of these silicon micropillar arrays depend on various parameters. In our previous work an optimum was found for pillars with a length of 40 µm and a junction depth of close to 1 µm.…”

The Study of Latex Sphere Lithography for High Aspect Ratio Dry Silicon Etching

“…The Bosch process allows obtaining vertical etching walls and an etching rate of about 2–50 μm min −1 . Unfortunately, the Bosch process is not suitable for solar cells due to the microroughness associated with the cyclical process . This roughness can lead to the formation of additional surface recombination centers at the amorphous/crystalline silicon interface.…”