WORK FUNCTION OF SOLAR CELL

Calculation of the Work Function at Materials Interfaces in Solar Cells

[Name of the Institute]

Table of Contents

CHAPTER 1: INTRODUCTION1

1.1 History1

1.2 Introduction2

Aims and Objectives5

Experimental Approach6

A short comparison with organic light emitting diodes8

Different organic solar cells families10

REFERENCING18

Calculation of the Work Function at Materials Interfaces in Solar Cells

CHAPTER 1: INTRODUCTION

1.1 History

The energy sector has a constrained future, since increasing demand coincides with “prise de conscience” of the negative implications of fossil energy use. Global warming is finally a clear evidence of the fundamental idea of the “old” Newtonian physics: there is no action without reaction. Fundamental principle neglected by the occidental world during the last century. That is to say, we cannot continue to emit continuously carbon dioxide, nitrogen dioxide… and others pollutants produced from the burning of fossil energies into our environment without suffering the consequences. Some environmental scientists have highlighted this problem for some time [Lüthi et al., Nature, 2008], but only now are some governments giving the issue the attention that it deserves. Man-made climate change is one of the greatest threats our world faces (Blochwitz, 2001, pp. 97).

Renewable energies issued from our natural environment, such as wind power, solar thermal, photovoltaic, geothermal heat, marine and hydro power…, can help reduce our dependence on fossil energies. The present review is dedicated to photovoltaic energy and more precisely to some specific photovoltaic devices based on organic materials. Photovoltaic cells belong to the family of the optoelectronic devices.

As evidenced by their denomination, such devices use the optical and electronic transport properties of different materials to either produce electromagnetic radiation (light emitting diodes) or to generate electricity (photovoltaic cells -PV cells) (Zehner, 1999, pp. 1121). Photovoltaic cells also called solar cells are used to generate electrical power. A PV cell is a device based on the photoconductive properties of semiconductor materials -for carriers generation- coupled with the ability of these semiconductors to form junctions -for carriers' separation. The photoconductivity is the process in which electromagnetic energy is absorbed by a material and converted to excitation energy of electric charge carriers so that the material becomes quite conductor. When irradiated by a light, PV cells produce electrical energy across any connected external load.

1.2 Introduction

The occurrence of a photo-induced electron transfer from non-degenerate ground-state conjugated polymers to fullerenes allows us to explore them as materials for photovoltaic applications w1,2x. The excellent photosensitivity and relatively high-energy conversion efficiencies obtained from interpenetrating network bulk-heterojunction devices are promising. We have recently demonstrated that the power conversion efficiency of bulk heterojunction plastic solar cells produced from a soluble poly(para-phenylene vinylene) (MDMOPPV) and a soluble methanofullerene (PCBM) can be improved up to 2.5% under AM1.5 irradiation w3,4x, thus already reaching a power performance close to industrial application (Bagus, 2002, pp. 26).

The built-in potential of solar cells, which can be estimated from the open circuit voltage VOC, is an essential parameter of thin film photovoltaic devices, influencing charge dissociation and charge collection and thus mirroring the diode principle as well as the photophysical properties of ...