Physics of Solar Cells : From Principles to New Concepts

by Peter Würfel (University of Karlsruhe, Germany)

• ISBN13: 9783527404285
• ISBN10: 3527404287
• Format: Hardcover
• Copyright: 2005-03-01
• Publisher: Wiley-VCH

Summary

Wurfel's book describes in detail all aspects of solar cell function, the physics behind every single step, as well as all the issues to be considered when improving solar cells and their efficiency. Based on the highly successful German version, but thoroughly revised and updated, this edition contains the latest knowledge on the mechanisms of solar energy conversion. Requiring no more than standard physics knowledge, it enables readers to understand the factors driving conversion efficiency and to apply this knowledge to their own solar cell development.

Author Biography

Peter Wurfel was Professor at the University of Karlsruhe.

Table of Contents

List of Symbols	ix
Preface	xi
1 Problems of the Energy Economy	1	(8)
1.1 Energy economy	1	(2)
1.2 Estimate of the maximum reserves of fossil energy	3	(2)
1.3 The greenhouse effect	5	(4)
1.3.1 Combustion	5	(1)
1.3.2 The temperature of the earth	6	(3)
2 Photons	9	(28)
2.1 Black-body radiation	9	(10)
2.1.1 Photon density ηγ in a cavity (Planck's law of radiation)	9	(5)
2.1.2 Energy current through an area dΑ into the solid angle dΩ	14	(2)
2.1.3 Radiation from a spherical surface into the solid angle dΩ	16	(1)
2.1.4 Radiation from a surface element into a hemisphere (Stefan-Boltzmann radiation law)	17	(2)
2.2 Kirchhoff's law of radiation for non-black bodies	19	(2)
2.2.1 Absorption by semiconductors	21	(1)
2.3 The solar spectrum	21	(3)
2.3.1 Air Mass	23	(1)
2.4 Concentration of the solar radiation	24	(5)
2.4.1 The Abbé sine condition	26	(1)
2.4.2 Geometrical optics	26	(2)
2.4.3 Concentration of radiation using the sine condition	28	(1)
2.5 Maximum efficiency of solar energy conversion	29	(8)
3 Semiconductors	37	(48)
3.1 Electrons in semiconductors	38	(7)
3.1.1 Distribution function for electrons	38	(1)
3.1.2 Density of states De(epsilone) for electrons	39	(4)
3.1.3 Density of electrons	43	(2)
3.2 Holes	45	(2)
3.3 Doping	47	(4)
3.4 Quasi-Fermi distributions	51	(7)
3.4.1 Fermi energy and electrochemical potential	53	(4)
3.4.2 Work function	57	(1)
3.5 Generation of electrons and holes	58	(7)
3.5.1 Absorption of photons	59	(3)
3.5.2 Generation of electron-hole pairs	62	(3)
3.6 Recombination of electrons and holes	65	(14)
3.6.1 Radiative recombination, emission of photons	65	(2)
3.6.2 Non-radiative recombination	67	(10)
3.6.3 Lifetimes	77	(2)
3.7 Light emission by semiconductors	79	(6)
3.7.1 Transition rates and absorption coefficient	79	(6)
4 Conversion of Thermal Radiation into Chemical Energy	85	(8)
4.1 Maximum efficiency for the production of chemical energy	88	(5)
5 Conversion of Chemical Energy into Electrical Energy	93	(16)
5.1 Transport of electrons and holes	93	(5)
5.1.1 Field current	94	(1)
5.1.2 Diffusion current	95	(1)
5.1.3 Total charge current	96	(2)
5.2 Separation of electrons and holes	98	(3)
5.3 Diffusion length of minority carriers	101	(1)
5.4 Dielectric relaxation	102	(1)
5.5 Ambipolar diffusion	103	(1)
5.6 Dember effect	104	(2)
5.7 Mathematical description	106	(3)
6 Basic Structure of Solar Cells	109	(28)
6.1 A chemical solar cell	109	(3)
6.2 Basic mechanisms in solar cells	112	(2)
6.3 Dye solar cell	114	(1)
6.4 The pn-junction	115	(10)
6.4.1 Electrochemical equilibrium of electrons in a pn-junction in the dark	116	(1)
6.4.2 Potential distribution across a pn-junction	117	(3)
6.4.3 Current-voltage characteristic of the pn-junction	120	(5)
6.5 pn-junction with impurity recombination, two-diode model	125	(2)
6.6 Hetero-junctions	127	(2)
6.7 Semiconductor-metal contact	129	(4)
6.7.1 Schottky contact	131	(1)
6.7.2 MIS contact	132	(1)
6.8 The role of the electric field in solar cells	133	(4)
7 Limitations on Energy Conversion in Solar Cells	137	(18)
7.1 Maximum efficiency of solar cells	137	(3)
7.2 Efficiency of solar cells as a function of their energy gap	140	(1)
7.3 The optimal silicon solar cell	141	(6)
7.3.1 Light trapping	142	(5)
7.4 Thin-film solar cells	147	(2)
7.4.1 Minimal thickness of a solar cell	147	(2)
7.5 Equivalent circuit	149	(1)
7.6 Temperature dependence of the open-circuit voltage	149	(2)
7.7 Intensity dependence of the efficiency	151	(1)
7.8 Efficiencies of the individual energy conversion processes	151	(4)
8 Concepts for Improving the Efficiency of Solar Cells	155	(22)
8.1 Tandem cells	155	(5)
8.1.1 The electrical interconnection of tandem cells	158	(2)
8.2 Concentrator cells	160	(1)
8.3 Thermo-photovoltaic energy conversion	161	(2)
8.4 Impact ionization	163	(5)
8.4.1 Hot electrons from impact ionization	165	(1)
8.4.2 Energy conversion with hot electrons and holes	165	(3)
8.5 Two-step excitation in three-level systems	168	(9)
8.5.1 Impurity photovoltaic effect	168	(4)
8.5.2 Up- and down-conversion of photons	172	(5)
9 Prospects for the Future	177	(4)
Appendix	181	(2)
Index	183