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Photovoltaics: The Basics

Vítezslav Benda
ˇ
CZECH TECHNICAL UNIVERSITY IN PRAGUE, PRAGUE, CZECH REPUBLIC
benda@fel.cvut.cz

8.1 Introduction

The photovoltaic (PV) industry has recently shown an unprecedented rate of growth with
the installed global PV power increasing by more than 30-fold over the last 10 years: from
9.1 GW p in 2007 to over 300 GW p in 2016. This impressive progress has been due to a num-
ber of factors, including a lowering to production costs, an increase in PV panel efficiency,
and a greater improvement in PV panel reliability.
The success of the PV industry lies with the development of the PV (solar) cells. PV cells
are simply semiconductor diode structures that have been carefully designed and con-
structed to efficiently absorb and convert solar irradiation energy into electrical energy.
For practical purposes, PV cells are interconnected and environmentally protected in PV
modules that form the basic elements of PV systems.
This chapter introduces the basic principles and information concerning PV cells,
module, characteristics, and design rules. Monographs [1–7] describing particular phe-
nomena in details are used as references.

8.2 Light Absorption in Materials and Excess Carrier
Generation

Light of the wavelength λ can be represented by a flux of photons that have energy hc/λ
8
−1
(h = 6.626 × 10 −34 J s is the Planck’s constant and c = 2.998 × 10 ms is speed of the light
in vacuum). When a flux of photons Φ in falls on a material surface, a part is reflected and a
part, the flux of photons Φ 0 , penetrates the material
λ = Φ ()[1
Φ () in λ − R λ()], (8.1) Φ 0 (λ)=Φin(λ)[1−R(λ)],
0
where R λ() is the surface reflectivity that depends on the photon energy. R(λ)
The photons penetrating into the material interact with material particles. In the case
of monochromatic light of wavelength λ, the interaction can be considered as an interac-
tion of a photon with energy hν = hc/λ and momentum ≈0 with the particles of the material
(electrons and nucleus). The interaction has to satisfy the conservation of both energy and

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