Theory of solar cells

Résumé

The theory of solar cells explains the process by which light energy in photons is converted into electric current when the photons strike a suitable semiconductor device. The theoretical studies are of practical use because they predict the fundamental limits of a solar cell, and give guidance on the phenomena that contribute to losses and solar cell efficiency. Working explanation

Photons in sunlight hit the solar panel and are absorbed by semi-conducting materials.

Electrons (negatively charged) are knocked loose from their atoms as they are excited. Due to their special structure and the materials in solar cells, the electrons are only allowed to move in a single direction. The electronic structure of the materials is very important for the process to work, and often silicon incorporating small amounts of boron or phosphorus is used in different layers.

An array of solar cells converts solar energy into a usable amount of direct current (DC) electricity.

Photo

Source officielle

https://en.wikipedia.org/wiki/Theory_of_solar_cells

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (9)

Chargement

Afficher plus

Publications associées

Chargement

Personnes associées

Aucun résultat

Personnes associées

Chargement

Unités associées

Chargement

Concepts associés (6)

Concepts associés

Chargement

Cours associés (3)

Cours associés

Chargement

Séances de cours associées (9)

Séances de cours associées

Chargement

Publications associées (9)

Solar photovoltaic energy production relies on the direct conversion of sunlight into electricity. Silicon thin-film solar cells represent a reliable and environmentally friendly technology to make photovoltaics economically viable. As these solar cells do not contain any rare or toxic materials they are an ideal candidate for the large scale deployment of solar energy. At the same time photovoltaic energy production is ideal for off-grid, stand-alone installations. This thesis presents new methods and results on computational engineering of thin-film silicon solar cells and modules. Computational engineering employs numerical methods and simulation techniques to address engineering challenges. Predictive numerical simulations allow for device optimizations that otherwise require substantial experimental effort and they may lead to new insights into the device physics which is the basis for further improvements in terms of cell efficiency and lifetime. We discuss the development of two new simulation methods and present several case studies that illustrate their use in solar cell characterization and optimization. The first presented method addresses optical simulations, i.e. the interaction of the solar cell with sunlight. Our optical model is based on the net-radiation method that considers incoherent, ray-like propagation of light. We extend the net-radiation method with thin-film optics to allow for arbitrary sequences of thick and thin layers. Experimentally, advanced techniques such as optimized surface textures have been developed to increase the absorption in the solar cell and thereby to increase the produced current. We illustrate how our optical model takes into account these textures by means of azimuth integrated light scattering properties to formulate a computationally efficient model of light propagation within the solar cell. Our optical model thus integrates coherent and incoherent propagation of light as well as a non-iterative treatment of ligth scattering. It bridges the gap between wave and ray optics that alternative approaches are most often facing. We first apply the method to study a recently proposed rear electrode architecture based on lithium fluoride and aluminum in amorphous silicon solar cells. Our model-based optical analysis identifies the increased reflectivity of this back electrode as its main advantage. Secondly, we then explore the potential performance gains in microcrystalline silicon solar cells that can be reached by eliminating absorption in layers that do not contribute to the photogeneration of solar cell current. Finally, our optical model is also suited for other solar cell technologies and we illustrate its extension and application to light extraction calculations in light emitting diodes (LEDs). Our optical model has been incorporated into the software package setfos, commercialized by Fluxim Inc. It is thus available to the research community. We then turn to address large area solar modules. A new method based on the finite element method (FEM) is presented to calculate the electrical charge and heat transport in these devices and how it is influenced by defects as well as partial shading. We identify such defects with surface temperature measurements by means of lock-in thermography and demonstrate how our model accounts for the thermal signature of localized defects. Taking into account the large aspect ratio of thin-film solar modules we show how geometrical projections can be used to reduce the model complexity, leading to a numerically efficient approach based on the finite element method. We demonstrate this by presenting full current-voltage curves of solar modules under partial shading.

EPFL2013

Chargement

Insights into photovoltaic properties of ternary organic solar cells from phase diagrams

Surendra Babu Anantharaman, Roland Hany, Jakob Heier, Philippe Schwaller

The efficiency of ternary organic solar cells relies on the spontaneous establishment of a nanostructured network of donor and acceptor phases during film formation. A fundamental understanding of phase composition and arrangement and correlations to photovoltaic device parameters is of utmost relevance for both science and technology. We demonstrate a general approach to understanding solar cell behavior from simple thermodynamic principles. For two ternary blend systems we construct and model phase diagrams. Details of EQE and solar cell parameters can be understood from the phase behavior. Our blend system is composed of PC70BM, PBDTTT-C and a near-infrared absorbing cyanine dye. Cyanine dyes are accompanied by counterions, which, in a first approximation, do not change the photophysical properties of the dye, but strongly influence the morphology of the ternary blend. We argue that counterion dissociation is responsible for different mixing behavior. For the dye with a hexafluorophosphate counterion a hierarchical morphology develops, the dye phase separates on a large scale from PC70BM and cannot contribute to photocurrent. Differently, a cyanine dye with a TRISPHAT counterion shows partial miscibility with PC70BM. A large two-phase region dictated by the PC70BM: PBDTTT-C mixture is present and the dye greatly contributes to the short-circuit current.

2018

Chargement

Optical and electrical properties of hydrogenated nanocrystalline silicon (nc-Si:H) solar cells are strongly influenced by the morphology of underlying substrates. By texturing the substrates, the photogenerated current of nc-Si:H solar cells can increase due to enhanced light scattering. These textured substrates are, however, often incompatible with defect-less nc-Si:H growth resulting in lower Vo. and FF. In this study we investigate the correlation between the substrate morphology, the nc-Si:H solar-cell performance, and the defect density in the intrinsic layer of the solar cells (i-nc-Si:H). Statistical surface parameters representing the substrate morphology do not show a strong correlation with the solar-cell parameters. Thus, we first quantify the line density of potentially defective valleys of randomly textured ZnO substrates where the opening angle is smaller than 130 degrees (rho(

Amer Chemical Soc2016

Chargement

Afficher plus

EPFL2013