Physics of photovoltaic processes 

Objectives

This course concerns the main physical phenomena that occur in the active material of a photovoltaic cell: the absorption of light, the charge generation, transport.

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.

Syllabus

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 PHOTOGENERATIO

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.

Assessment

A numerical model regarding device simulation will be discussed, followed by an oral presentation on a specified sub topic of the program