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

(Oxy)nitride materials, consisting mainly of transition metal and ionic-covalent (oxy)nitrides, show a vast number of interesting physical and chemical properties due to their substantial structural diversity. The optical properties of these (oxy)nitrides, in combination with their excellent mechanical strength, thermal properties, and chemical stability, enable (oxy)nitrides to be used in a variety of industrial fields, such as photovoltaic, photothermal, photocatalytic, pigment, lighting and display, optoelectronic, and defense industries. The optical properties are extremely related to the electronic band structure of (oxy)nitrides, and can be varied significantly by changing the chemical composition (e.g., the oxygen to nitrogen ratio) and preparation/processing conditions. This article overviews the optical properties (including refractive index, reflectance, absorbance, band gap, photoluminescence, and transmittance) of (oxy)nitride materials that are in the form of thin films, powders, or bulk ceramics, and highlights their applications as antireflection coatings, solar spectral selectivity coatings, visible-light-driven photocatalysts, ecological pigments, phosphors for light-emitting diodes, and transparent window materials.

Optical Properties of (Oxy)Nitride Materials: A Review

Silicon wafer solar cells continue to be the leading photovoltaic technology, and in many places are now providing a substantial portion of electricity generation. Further adoption of this technology will require processing that minimises losses in device performance. A fundamental mechanism for efficiency loss is the recombination of photo-generated charge carriers at the unavoidable cell surfaces. Dielectric coatings have been shown to largely prevent these losses through a combination of different passivation mechanisms. This review aims to provide an overview of the dielectric passivation coatings developed in the past two decades using a standardised methodology to characterise the metrics of surface recombination across all techniques and materials. The efficacy of a large set of materials and methods has been evaluated using such metrics and a discussion on the current state and prospects for further surface passivation improvements is provided.

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Dielectric surface passivation for silicon solar cells: A review

Crystalline silicon (c-Si) solar cells featuring a high-temperature processed homojunction have dominated the photovoltaic industry for decades, with a global market share of around 93%. Integrating commercially available crystalline silicon solar cells with high-efficiency perovskite solar cells is a viable pathway to increase the power conversion efficiency, and hence achieve low levelized electricity costs for the photovoltaic systems. However, the fabrication process for this type of cell is challenging due to the many, and often conflicting, material processing requirements and limitations. Here, we present an innovative design for a monolithic perovskite/silicon tandem solar cell, featuring a mesoscopic perovskite top subcell and a high-temperature tolerant homojunction c-Si bottom subcell. The improved temperature tolerance of the c-Si bottom cell permits significantly increased flexibility in the design and fabrication of the perovskite cell. We demonstrate an efficiency of 22.5% (steady-state) and a Voc of 1.75 V on a 1 cm2 cell. The method developed in this work opens up new possibilities in designing, fabricating and commercialising low-cost high-efficiency perovskite/c-Si tandem solar cells.

Monolithic perovskite/silicon-homojunction tandem solar cell with over 22% efficiency

24.58% total area efficiency of screen-printed, large area industrial silicon solar cells with the tunnel oxide passivated contacts (i-TOPCon) design

Optimised Antireflection Coatings using Silicon Nitride on Textured Silicon Surfaces based on Measurements and Multidimensional Modelling

monoPoly™ cells: Large-area crystalline silicon solar cells with fire-through screen printed contact to doped polysilicon surfaces

Approaching 23% with large‐area monoPoly cells using screen‐printed and fired rear passivating contacts fabricated by inline PECVD

By combining commonly available solar cell characterization methods with easy-to-prepare test structures and partially processed rear-passivated solar cells from the production line, we show that various cell loss mechanisms can be quantified in exquisite detail to generate process-related diagnostics. An example monocrystalline silicon localized back surface field solar cell type is examined using a systematic routine that breaks down the factors limiting open-circuit voltage, short-circuit current, and fill factor (FF) to identify the cell structure's headroom for improvement.

Shubham Duttagupta

Papers

Optimised Antireflection Coatings using Silicon Nitride on Textured Silicon Surfaces based on Measurements and Multidimensional Modelling

monoPoly™ cells: Large-area crystalline silicon solar cells with fire-through screen printed contact to doped polysilicon surfaces

Approaching 23% with large‐area monoPoly cells using screen‐printed and fired rear passivating contacts fabricated by inline PECVD

A Systematic Loss Analysis Method for Rear-Passivated Silicon Solar Cells

Metal contact recombination in monoPoly solar cells with screen-printed & fire-through contacts