This course concerns the main physical phenomena that occur in the active material of a photovoltaic cell: the absorption of light, the charge generation, the charge transport and recombination. The approach is phenomenological even if it makes extensive use of the concepts and basic tools of quantum mechanics, which are anyway briefly introduced. The proposed models are then compared with existing technologies, describing the photovoltaic cells of the first, second and third generation. The goal is to provide the wealth of basic knowledge needed to design new materials for photovoltaics.

Students:

-will learn the fundamentals regarding photovoltaic cell devices

-will acquire knowledge on the state of art in photovoltaic conversion and on the existing technologies, both on the market and at research stage

-will learn the fundamental concepts in photophysics for designing and characterizing new materials and devices for photovoltaic conversion

INTRODUCTION

Solar radiation.

Ultimate theoretical limit of a cell and detailed balance.

Two level system,
Density matrix.

Susceptibility and refractive index.

ABSORPTION

Molecular absorption. Adibatic approximation, Vibronic linewidth and Franck-Condon principle.
Einstein A and B coefficients. Strickler-Berg relation.

Kasha molecular exciton in aggregates.

Energy transfer (Foerster, Dexter, Frenkel exciton).
Absorption in a crystal (band structure, carrier relaxation,
Wannier-Mott exciton, dimensionality).

MOLECULAR DYNAMICS

Jablonski diagram, internal conversion, vibrational energy redistribution, radiative decay, inter system crossing, phosphorescence. Mono and bi molecular recombination. Vavilov-Kasha rule.

CHARGE PHOTOGENERATION

Charge transfer states.

Marcus theory.
Band to band transition, Onsager, Poole-Frenkel. Donor-Acceptor system.

TRANSPORT

Mobility
Hopping in disordered systems.
Coherent transport.

Experimental techniques to determine mobility.

PHOTOVOLTAIC DEVICES

General characteristics of a PV cell.

Polymer solar cells.
Dye sensitized solar cells.
Inorganic semiconductor cells (Si p-n junction and thin films).
Luminescent solar collectors.
Natural systems.

It is assumed a basic knowledge on electromagnetic waves, atomic and molecular physics and radiation-matter interaction. A basic knowledge of quantum mechanics is useful, but it is not strictly required.

For students attending all lectures evaluation is based on assignments handed in during the course.

For those students randomly or not attending lectures an oral exam.