OVERVIEW

The course describes the physical mechanisms underlying the direct conversion of solar radiation into electrical energy by exploiting the photovoltaic effect. The fundamental thermodynamic limits for efficiency and the constraints on the choice of materials and on the construction parameters of high efficiency devices will therefore be understood. Finally, a laboratory activity aimed at electro-optical and morphological characterization of commercial solar cells is planned.

AIMS AND CONTENT

LEARNING OUTCOMES

The course aims to illustrate the potential of solar resources and the physical mechanisms underlying the conversion of solar radiation into electrical energy. The elements of semiconductor physics necessary to describe the functioning of solar cells will be introduced with particular reference to those in silicon. Finally, an overview of the new concepts and materials studied to increase the efficiency of solar cells will be provided.

AIMS AND LEARNING OUTCOMES

(i)The course objectives include the acquisition of theoretical knowledge related to: Solar energy resource and the sizing of photovoltaic production potential assessed through the use of reference simulation software (PVGIS) available on Open Access platforms. Optical absorption processes in semiconductors. Physics of solar cells and semiconductors, with particular reference to silicon junction devices. Thermodynamic limits to the efficiency of a photovoltaic converter and new concepts and materials to increase the efficiency of solar cells.

(ii) The student will be able to critically discuss the physical limits to the conversion efficiency of photovoltaic devices, and the effect on the efficiency of physical parameters and constituent materials.

(iii) The student will be able to apply the knowledge acquired to complete the correct sizing of a photovoltaic system, to estimate the potential of solar radiation and photovoltaic production in a specific location, also using open source software simulation tools (PVGIS). 

(iv) The educational objectives of the course also include the acquisition of experimental skills relatively to the electro-optical and morphological characterization of commercial solar cells.

The specific training activities and skills (i-iv) are indicated both for the "Materials Scientist: Research Specialist" profile and for the "Materials Scientist: Technology Specialist" profile. Activities (iii) and (iv) are also particularly relevant for the "Materials Scientist: Technology Specialist" profile.

PREREQUISITES

The knowledge of the basic concept of Solid Physics and Quantum Machanics are considered to be acquired with particular reference to the behavior of electrons in metals and semiconductors. A prerequisite is also the knowledge of general and Modern Physics Physics with particular reference to electromagnetism, optics and radiation-matter interaction.

TEACHING METHODS

The course comprises about 42 hours of classroom lectures in which the theoretical topics are presented. Approximately 8 hours of laboratory activity are also planned in which the characterization of commercial solar cells is carried out with regards to their optical response in terms of spectral reflectivity, morphology and structure of the light-trapping layer, their electro-optical response under illuminated conditions by measuring the I-V curves and the quantum efficiency.

The laboratory experience is preceded by a preparatory/planning phase carried out in the classroom with the teacher or by the group. Students will have to learn how to manage the limited time required to carry out measurements, data analysis and drafting of the written report. Each of the reports will be evaluated by the teachers from time to time so as to allow students to become aware of their own preparation. This will allow to develop the soft skills mentioned in the LEARNING OBJECTIVES section.

SYLLABUS/CONTENT

1. Introduction:

renewable energy, global warming, energy policy

2- Solar energy resource:

Solar radiation. Spectrum of a black body; Effects terrestrial atmosphere on solar radiation: absorption from atoms and molecules and spectral distribution of solar radiation. Absorption from semiconductors; Optical processes; Concentration of solar radiation;

3- Physics of solar cells:

Recalls of semiconductor physics. Absorption of photons and generation of electron-hole pairs; Recombination of electrons and holes (radiative and non-radiative). Recombination at grain boundaries, defects and surfaces; Dissemination of minority carriers; lifetime and diffusion length of minority carriers;

4- Basic structure of a Silicon solar cell:

p-n and p-i-n Junction . Separation of electrons and holes; I-V characteristic of a solar cell. Monocrystalline solar cells; Polycrystalline solar cells; Theoretical limits for energy conversion (Schockley-Queisser approach); Efficiency and energy gap; Spectral response; Effect of parasitic resistances; temperature effects;

5- New concepts and materials to increase the efficiency of solar cells:

Losses by reflection; Concentrating solar cells. Thin-film solar cells; Amplification of Photon Collection in nanostructured cells; Introduction to other semiconductor materials of photovoltaic interest; Thermodynamic limits to the efficiency of a thermodynamic solar converter; Tandem cells (multi-junction) (outline). Intermediate band cells (outline); Cells with warm carriers (outline); Impact ionization cells (outline).

6- Laboratory activities

Electro-optical and morphological characterization of commercial solar cells

RECOMMENDED READING/BIBLIOGRAPHY

• “Handbook of Photovoltaic Science and Engineering” Eds. A.Luque and S. Hegedus, Wiley
• “The Physics of Solar cells” by Jenny Nelson (Imperial College, UK) World Scientific Press
•  “Materials Concepts for Solar Cells” by Thomas Dittrich (Imperial College Press) 2nd edition

TEACHERS AND EXAM BOARD

Exam Board

FRANCESCO BUATIER DE MONGEOT (President)

MATTEO BARELLI

MARIA CATERINA GIORDANO (President Substitute)

CORRADO BORAGNO (Substitute)

DAVIDE COMORETTO (Substitute)

LESSONS

LESSONS START

Normally the start of lessons is scheduled during the first week of March.

Class schedule

The timetable for this course is available here: Portale EasyAcademy

EXAMS

EXAM DESCRIPTION

The exam will consist in an oral interview lasting about 45 minutes, on a date that can be agreed with the teacher who must be contacted well in advance.
The oral exam will be held in the presence of two professors belonging to the commission, at least one of which chosen between F. Buatier de Mongeot and M.C. Giordano.
During the exam the student can illustrate one of the topics of the program of his choice (about 1/3 of the test) while the remaining time of the test is dedicated to deepening the remaining parts of the program.

ASSESSMENT METHODS

During the oral exam, the actual achievement of the expected learning outcomes will be verified. The level of knowledge acquired on specific points of the program will be verified, the degree of understanding with respect to the role of the physical mechanisms that determine the operation and efficiency of a photovoltaic device, and the critical ability in dealing with specific cases set by the teacher. The quality of the exposure, the correct use of the specialist vocabulary, the ability to reason critically with respect to specific cases posed by the teacher are also assessed.

Exam schedule