Fa-Jun Ma

Bio: Fa-Jun Ma is an academic researcher from National University of Singapore. The author has contributed to research in topics: Silicon & Passivation. The author has an hindex of 10, co-authored 27 publications receiving 388 citations. Previous affiliations of Fa-Jun Ma include Agency for Science, Technology and Research.

Advanced modeling of the effective minority carrier lifetime of passivated crystalline silicon wafers

Abstract: A strong injection level dependence of the effective minority carrier lifetime (τeff) is typically measured at low injection levels for undiffused crystalline silicon (c-Si) wafers symmetrically passivated by a highly charged dielectric film. However, this phenomenon is not yet well understood. In this work, we concentrate on two of those possible physical mechanisms to reproduce measured τeff data of c-Si wafers symmetrically passivated by atomic layer deposited Al2O3. The first assumes the existence of a defective region close to the c-Si surface. The second assumes asymmetric electron and hole lifetimes in the bulk. Both explanations result in an adequate reproduction of the injection dependent τeff found for both n- and p-type c-Si wafers. However, modeling also predicts a distinctly different injection dependence of τeff for the two suggested mechanisms if the polarity of the effective surface charge is inverted. We test this prediction by experimentally inverting the polarity of the effective surfac...

Modeling of Stress-Retarded Thermal Oxidation of Nonplanar Silicon Structures for Realization of Nanoscale Devices

Abstract: Accurate modeling of stress-retarded orientation-dependent 2-D oxidation is carried out by matching the experimental and simulated oxide thicknesses of silicon FIN nanostructures over a wide range of temperatures and times in dry oxygen. Experimentally observed initial oxidation rate enhancement, orientation-dependent stress retardation, and self-limiting phenomena are modeled, and a new universal stress retardation parameter set is obtained for the first time. The new parameter set has been validated against oxidation experiments presented here and those reported in the literature. Furthermore, the new model is used to explore silicon nanowire shape engineering.

Progress in Surface Passivation of Heavily Doped n-Type and p-Type Silicon by Plasma-Deposited AlO $_{\bm x}$ /SiN $_{\bm x}$ Dielectric Stacks

Abstract: We report an outstanding level of surface passivation for both n+ and p+ silicon by AlOx/SiNx dielectric stacks deposited in an inline plasma-enhanced chemical vapor deposition (PECVD) reactor for a wide range of sheet resistances. Extremely low emitter saturation current densities (J0e) of 12 and 200 fA/cm2 are obtained on 165 and 25 Ω/sq n+ emitters, respectively, and 8 and 45 fA/cm2 on 170 and 30 Ω/sq p+ emitters, respectively. Using contactless corona-voltage measurements and device simulations, we demonstrate that the surface passivation mechanism on both n+ and p + silicon is primarily due to a relatively low interface defect density of <;1011 eV-1cm-2 in combination with a moderate fixed negative charge density of (1-2) × 1012 cm-2. From advanced modeling, the fundamental surface recombination velocity parameter is shown to be in the order of 104 cm/s for PECVD AlOx/SiNx passivated heavily doped n+ and p+ silicon surfaces.

Black silicon: fabrication methods, properties and solar energy applications

Abstract: 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.

Optical Properties of (Oxy)Nitride Materials: A Review

Abstract: (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.

Dielectric surface passivation for silicon solar cells: A review

Abstract: 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.

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

Abstract: 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.

Input Parameters for the Simulation of Silicon Solar Cells in 2014

Abstract: Within the silicon photovoltaics (PV) community, there are many approaches, tools, and input parameters for simulating solar cells, making it difficult for newcomers to establish a complete and representative starting point and imposing high requirements on experts to tediously state all assumptions and inputs for replication In this review, we address these problems by providing complete and representative input parameter sets to simulate six major types of crystalline silicon solar cells Where possible, the inputs are justified and up-to-date for the respective cell types, and they produce representative measurable cell characteristics Details of the modeling approaches that can replicate the simulations are presented as well The input parameters listed here provide a sensible and consistent reference point for researchers on which to base their refinements and extensions