The reduction in electronic recombination losses by the passivation of silicon surfaces is a critical enabler for high-efficiency solar cells. In 2006, aluminum oxide (Al2O3) nanolayers synthesized by atomic layer deposition (ALD) emerged as a novel solution for the passivation of p- and n-type crystalline Si (c-Si) surfaces. Today, high efficiencies have been realized by the implementation of ultrathin Al2O3 films in laboratory-type and industrial solar cells. This article reviews and summarizes recent work concerning Al2O3 thin films in the context of Si photovoltaics. Topics range from fundamental aspects related to material, interface, and passivation properties to synthesis methods and the implementation of the films in solar cells. Al2O3 uniquely features a combination of field-effect passivation by negative fixed charges, a low interface defect density, an adequate stability during processing, and the ability to use ultrathin films down to a few nanometers in thickness. Although various methods can be used to synthesize Al2O3, this review focuses on ALD—a new technology in the field of c-Si photovoltaics. The authors discuss how the unique features of ALD can be exploited for interface engineering and tailoring the properties of nanolayer surface passivation schemes while also addressing its compatibility with high-throughput manufacturing. The recent progress achieved in the field of surface passivation allows for higher efficiencies of industrial solar cells, which is critical for realizing lower-cost solar electricity in the near future.

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Status and prospects of Al2O3-based surface passivation schemes for silicon solar cells

The miniaturization of power sources aimed at integration into micro- and nano-electronic devices is a big challenge. To ensure the future development of fully autonomous on-board systems, electrodes based on self-supported 3D nanostructured metal oxides have become increasingly important, and their impact is particularly significant when considering the miniaturization of energy storage systems. This review describes recent advances in the development of self-supported 3D nanostructured metal oxides as electrodes for innovative power sources, particularly Li-ion batteries and electrochemical supercapacitors. Current strategies for the design and morphology control of self-supported electrodes fabricated using template, lithography, anodization and self-organized solution techniques are outlined along with different efforts to improve the storage capacity, rate capability, and cyclability.

Three‐Dimensional Self‐Supported Metal Oxides for Advanced Energy Storage

Batteries have become fundamental building blocks for the mobility of modern society. Continuous development of novel battery chemistries and electrode materials has nourished progress in building better batteries. Simultaneously, novel device form factors and designs with multi-functional components have been proposed, requiring batteries to not only integrate seamlessly to these devices, but to also be a multi-functional component for a multitude of applications. Thus, in the past decade, along with developments in the component materials, the focus has been shifting more and more towards novel fabrication processes, unconventional configurations, and additional functionalities. This work attempts to critically review the developments with respect to emerging electrochemical energy storage configurations, including, amongst others, paintable, transparent, flexible, wire or cable shaped, ultra-thin and ultra-thick configurations, as well as hybrid energy storage-conversion, or graphene-incorporated batteries and supercapacitors. The performance requirements are elaborated together with the advantages, but also the limitations, with respect to established electrochemical energy storage technologies. Finally, challenges in developing novel materials with tailored properties that would allow such configurations, and in designing easier manufacturing techniques that can be widely adopted are considered.

Design Considerations for Unconventional Electrochemical Energy Storage Architectures

Applications of the non-line-of-sight vapor deposition techniques, such as chemical vapor deposition (CVD) and atomic layer deposition (ALD), offer unique opportunities to produce well-defined high surface area current collectors, thin films or various nanostructures of active (ion-storage) materials, protective coatings, solid electrolytes and improved separators. These features hold significant promise for solving emerging issues in advanced LiBs and supercapacitors. This paper reviews recent developments and applications of CVD and ALD for these energy storage devices, providing selected examples and outlining critical challenges for further exploration.

Chemical vapor deposition and atomic layer deposition for advanced lithium ion batteries and supercapacitors

Addressing Interfacial Issues in Liquid-Based and Solid-State Batteries by Atomic and Molecular Layer Deposition

The influence of a short high-temperature step, comparable to the so-called “firing” of the metallization on silicon solar cells, on properties of high-rate (>0.5 nm/s) plasma deposited silicon nitride (a-SiNx:H) films has been investigated. These a-SiNx:H films are used as antireflection coating on multicrystalline silicon (mc-Si) solar cells and, after the firing process, they also induce hydrogen bulk passivation in the mc-Si. Three different types of remote plasma deposited a-SiNx:H films have been investigated: (i) expanding thermal plasma (ETP) deposited a-SiNx:H films from a N2–SiH4 gas mixture, (ii) ETP deposited a-SiNx:H films from a NH3–SiH4 mixture, and (iii) microwave plasma deposited a-SiNx:H films from a NH3–SiH4 mixture. The atomic composition and optical and structural properties of the films have been studied before and after the high-temperature step by the combination of elastic recoil detection, spectroscopic ellipsometry, and Fourier transform infrared spectroscopy. It has been observed that the high-temperature step can induce significant changes in hydrogen content, bonding types, mass density, and optical absorption of the films. These thermally induced effects are more enhanced for Si- than for N-rich films, which in some cases have a high thermal stability. Furthermore, the material properties and the influence of the high-temperature step have been related to the bulk passivation properties of the a-SiNx:H coated mc-Si solar cells. It is found that in particular the density and thermal stability of the a-SiNx:H films seem to be important for the degree of the bulk passivation obtained.

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Influence of the high-temperature “firing” step on high-rate plasma deposited silicon nitride films used as bulk passivating antireflection coatings on silicon solar cells

One of the remaining challenges in the field of portable electronics is the miniaturization of lithium-ion batteries. To prepare all-solid-state batteries with a sufficient high storage capacity it is vital to prepare high quality thin films for battery stacks on 3D-structured substrates. A remote plasma atomic layer deposition (ALD) process has therefore been developed for LiCoO2 which can serve as a cathode material. A combination of CoCp2 as cobalt precursor, LiOtBu as lithium precursor and O2 plasma as oxidant source was used to create super-cycles to deposit LiCoO2 from Co3O4 and Li2CO3 cycles. The thin films were deposited at a temperature of 325°C and showed linear growth with a rate of 0.06 nm/cycle. After annealing the samples at 700°C for 6 minutes high temperature phase LiCoO2 was obtained, as was demonstrated by XRD and Raman spectroscopy. A new procedure was proposed to obtain the composition of all three chemical elements in the LiCoO2 films. Elastic Backscattering Spectroscopy (EBS) measurements turned out to be very convenient and reliable to obtain the quantities of all chemical elements, including lithium. Moreover, the ALD-deposited LiCoO2 thin film electrodes were electrochemically characterized, revealing good electrochemical performance. To the best of our knowledge this paper provides the first evidence that electrochemically active LiCoO2 can be deposited by ALD.

https://iopscience.iop.org/article/10.1149/2.011305jes/pdf

WM Wim ArnoldBik

Papers

Influence of the high-temperature “firing” step on high-rate plasma deposited silicon nitride films used as bulk passivating antireflection coatings on silicon solar cells

Atomic Layer Deposition of LiCoO2 Thin-Film Electrodes for All-Solid-State Li-Ion Micro-Batteries