Global environmental concerns and the escalating demand for energy, coupled with steady progress in renewable energy technologies, are opening up new opportunities for utilization of renewable energy resources. Solar energy is the most abundant, inexhaustible and clean of all the renewable energy resources till date. The power from sun intercepted by the earth is about 1.8 × 1011 MW, which is many times larger than the present rate of all the energy consumption. Photovoltaic technology is one of the finest ways to harness the solar power. This paper reviews the photovoltaic technology, its power generating capability, the different existing light absorbing materials used, its environmental aspect coupled with a variety of its applications. The different existing performance and reliability evaluation models, sizing and control, grid connection and distribution have also been discussed. © 2011 Published by Elsevier Ltd.

A review of solar photovoltaic technologies

Semiconductor nanowires (NWs) have been studied extensively for over two decades for their novel electronic, photonic, thermal, electrochemical and mechanical properties. This comprehensive review article summarizes major advances in the synthesis, characterization, and application of these materials in the past decade. Developments in the understanding of the fundamental principles of "bottom-up" growth mechanisms are presented, with an emphasis on rational control of the morphology, stoichiometry, and crystal structure of the materials. This is followed by a discussion of the application of nanowires in i) electronic, ii) sensor, iii) photonic, iv) thermoelectric, v) photovoltaic, vi) photoelectrochemical, vii) battery, viii) mechanical, and ix) biological applications. Throughout the discussion, a detailed explanation of the unique properties associated with the one-dimensional nanowire geometry will be presented, and the benefits of these properties for the various applications will be highlighted. The review concludes with a brief perspective on future research directions, and remaining barriers which must be overcome for the successful commercial application of these technologies.

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25th Anniversary Article: Semiconductor Nanowires – Synthesis, Characterization, and Applications

With a global market share of about 90%, crystalline silicon is by far the most important photovoltaic technology today. This article reviews the dynamic field of crystalline silicon photovoltaics from a device-engineering perspective. First, it discusses key factors responsible for the success of the classic dopant-diffused silicon homojunction solar cell. Next it analyzes two archetypal high-efficiency device architectures – the interdigitated back-contact silicon cell and the silicon heterojunction cell – both of which have demonstrated power conversion efficiencies greater than 25%. Last, it gives an up-to-date summary of promising recent pathways for further efficiency improvements and cost reduction employing novel carrier-selective passivating contact schemes, as well as tandem multi-junction architectures, in particular those that combine silicon absorbers with organic–inorganic perovskite materials.

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High-efficiency crystalline silicon solar cells: status and perspectives

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

Al2O3 is a versatile high-κ dielectric that has excellent surface passivation properties on crystalline Si (c-Si), which are of vital importance for devices such as light emitting diodes and high-efficiency solar cells. We demonstrate both experimentally and by simulations that the surface passivation can be related to a satisfactory low interface defect density in combination with a strong field-effect passivation induced by a negative fixed charge density Qf of up to 1013 cm−2 present in the Al2O3 film at the interface with the underlying Si substrate. The negative polarity of Qf in Al2O3 is especially beneficial for the passivation of p-type c-Si as the bulk minority carriers are shielded from the c-Si surface. As the level of field-effect passivation is shown to scale with Qf2, the high Qf in Al2O3 tolerates a higher interface defect density on c-Si compared to alternative surface passivation schemes.

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On the c-Si surface passivation mechanism by the negative-charge-dielectric Al2O3

Very low surface recombination velocities on p-type silicon wafers passivated with a dielectric with fixed negative charge

Chemical deposition of Al2O3 thin films on Si substrates

In this article, we report on the use of direct plasma-enhanced chemical vapor deposited silicon nitride (SiNx) films deposited at low excitation frequency (440 kHz) on low-resistivity (1.5 Ω cm) p-type Czochralski silicon substrate surfaces with different textures, to elucidate the influence of microroughness of the substrate surface on the surface-passivating properties of thin SiNx films. Whereas flat surfaces get the best passivation from Si-rich SiNx films, the optimum passivation shifts towards stoichiometric nitride as the microroughness increases, which points to the increasing relative importance of a charge-induced field effect. When short high-temperature (firing) treatments are applied upon passivation layer deposition, the process window to yield good surface passivation broadens, although very Si-rich films tend to suffer from blistering.

Influence of stoichiometry of direct plasma-enhanced chemical vapor deposited SiNx films and silicon substrate surface roughness on surface passivation

High-efficiency solar cell using a thin porous silicon layer

The present invention provides a method for dielectric passivating the surface of a solar cell by accumulation of negative fixed charges of a first type at the interface between semiconductor material and a passivating material. According to the invention the passivating material comprises an oxide system, for example a binary oxide system, comprising Al2O3 and at least one metal oxide or metalloid oxide which enhances the tetrahedral structure of Al2O3, for example, an (Al2O3)x(TiO2)1-x alloy. In this way it is possible to combine the desirable properties from at least two different oxides, while eliminating the undesirable properties of each individual material. The oxide system can be deposited onto the semiconductor surface by means of a sol-gel method, comprising the steps of formation of the metal oxide and/or metalloid oxide sol and the aluminum solution and then carefully mixing these together under stirring and ultrasonic treatment. Thin films of the oxide system can then be deposited onto the semiconductor surface by means of spin coating followed by a temperature treatment.

Petko Vitanov

Papers

Very low surface recombination velocities on p-type silicon wafers passivated with a dielectric with fixed negative charge

Chemical deposition of Al2O3 thin films on Si substrates

Influence of stoichiometry of direct plasma-enhanced chemical vapor deposited SiNx films and silicon substrate surface roughness on surface passivation

High-efficiency solar cell using a thin porous silicon layer

Method for backside surface passivation of solar cells and solar cells with such passivation