The efficiency of solar cells with high-area, nanostructured surfaces is limited by surface and Auger charge-recombination processes, which can be slowed through appropriate levels of junction doping

An 18.2%-efficient black-silicon solar cell achieved through control of carrier recombination in nanostructures

Black silicon (BSi) represents a very active research area in renewable energy materials. The rise of BSi as a focus of study for its fundamental properties and potentially lucrative practical applications is shown by several recent results ranging from solar cells and light-emitting devices to antibacterial coatings and gas-sensors. In this paper, the common BSi fabrication techniques are first reviewed, including electrochemical HF etching, stain etching, metal-assisted chemical etching, reactive ion etching, laser irradiation and the molten salt Fray-Farthing-Chen-Cambridge (FFC-Cambridge) process. The utilization of BSi as an anti-reflection coating in solar cells is then critically examined and appraised, based upon strategies towards higher efficiency renewable solar energy modules. Methods of incorporating BSi in advanced solar cell architectures and the production of ultra-thin and flexible BSi wafers are also surveyed. Particular attention is given to routes leading to passivated BSi surfaces, which are essential for improving the electrical properties of any devices incorporating BSi, with a special focus on atomic layer deposition of Al2O3. Finally, three potential research directions worth exploring for practical solar cell applications are highlighted, namely, encapsulation effects, the development of micro-nano dual-scale BSi, and the incorporation of BSi into thin solar cells. It is intended that this paper will serve as a useful introduction to this novel material and its properties, and provide a general overview of recent progress in research currently being undertaken for renewable energy applications.

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Black silicon: fabrication methods, properties and solar energy applications

The evolution of silicon cryoetching is reported in this topical review, from its very first introduction by a Japanese team to today's advanced technologies. The main advances in terms of the performance and comprehension of the mechanisms are chronologically presented. After presenting the principle of silicon cryoetching, the main defects encountered in cryoetching (such as undercut, bowing and crystal orientation dependent etching) are presented and discussed. Mechanisms involved in SiOxFy passivation layer growth in standard cryoetching are investigated through several in situ characterization experiments. The STiGer process and alternative cryoetching processes for high-aspect-ratio structures are also proposed to enhance the process robustness. The over-passivation regime, which can provide self-organized columnar microstructures, is presented and discussed. Finally, advanced technologies, such as the cryoetching of sub-20 nm features and porous OSG low-k cryoetching, are described.

https://iopscience.iop.org/article/10.1088/0022-3727/47/12/123001/pdf

Plasma cryogenic etching of silicon: from the early days to today's advanced technologies

We investigate the optical and opto-electronic properties of black silicon (b-Si) nanostructures passivated with Al2O3. The b-Si nanostructures significantly improve the absorption of silicon due to superior anti-reflection and light trapping properties. By coating the b-Si nanostructures with a conformal layer of Al2O3 by atomic layer deposition, the surface recombination velocity can be effectively reduced. We show that control of plasma-induced subsurface damage is equally important to achieve low interface recombination. Surface recombination velocities of Seff<13 cm/s have been measured for an optimized structure which, like the polished reference, exhibits lifetimes in the millisecond range.

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Extremely low surface recombination velocities in black silicon passivated by atomic layer deposition

This article presents an overview of the fabrication methods of black silicon, their resulting morphologies, and a quantitative comparison of their optoelectronic properties. To perform this quantitative comparison, different groups working on black silicon solar cells have cooperated for this study. The optical absorption and the minority carrier lifetime are used as benchmark parameters. The differences in the fabrication processes plasma etching, chemical etching, or laser processing are discussed and compared with numerical models. Guidelines to optimize the relevant physical parameters, such as the correlation length, optimal height of the nanostructures, and the surface defect densities for optoelectronic applications are given.

Black Silicon Photovoltaics

Large-area multicrystalline silicon solar cell fabrication using reactive ion etching (RIE)

Front surface texturing processed by wet or dry etching improves efficiencies of solar cells, due to reduced reflection and light trapping with antireflection coatings. Random reactive ion etching (RIE) techniques are very effective for application with low-cost, large area crystalline silicon solar cells. In this paper, we studied a SF 6 /O 2 RIE process without mask texturing of silicon. By this process, pyramids of needle-like structure (with diameters ranging from 50 nm to 70 nm) were formatted by local and regenerating oxide masking and inhomogeneous etching. After the RIE process, we also investigated damage removal etching (DRE) as a function of the etching time to determine which produced the highest cell performance for screen-printed cell fabrication sequences. Crystalline silicon solar cells fabricated in a conventional industrial production line applying optimized film deposition and annealing conditions on a large area substrate (125 mm × 125 mm) had conversion efficiencies as high as 15.1%.

Gwonjong Yu

Papers

Large-area multicrystalline silicon solar cell fabrication using reactive ion etching (RIE)

Black surface structures for crystalline silicon solar cells

Study on hydrogenated silicon nitride for application of high efficiency crystalline silicon solar cells