Preface by Richard H. Friend .................................. vii
List of abbreviations ......................................... ix
Introduction .................................................. xi
Part One: Concepts: Electronic and optical
processes in organic solids
Chapter I: Band and electronic structures in
regular 1-dimensional media .................................... 3
I. An introduction to approximations of weak and
strong bonds ............................................... 3
1. Materials with weak bonds ............................... 3
2. Materials with strong bonds ............................. 4
II. Band Structure in weak bonds ............................... 6
1. Prior result for zero order
approximation ........................................... 6
2. Physical origin of forbidden bands ...................... 6
3. Simple estimation of the size of the
forbidden band .......................................... 8
III. Floquet's theorem: wavefunctions for strong
bonds ...................................................... 9
1. Form of the resulting potential ......................... 9
2. The form of the wavefunction ........................... 10
3. Floquet's theorem: effect of potential
periodicity on wavefunction form ....................... 11
IV. A study on energy ......................................... 12
1. Defining equations (with x ≡ r: 1 — D) ................. 12
2. Calculation of energy for a chain of N
atoms .................................................. 13
3. Additional comments: physical significance
of terms (E0 — α) and β simple
calculation of E; and the appearance of
allowed and forbidden bands in strong
bonds .................................................. 16
V. 1-D crystal and the distorted chain ....................... 19
1. AB type crystal ........................................ 19
2. The distorted chain .................................... 20
VI. Density function and its application, the
metal insulator transition and calculation of
Erelax ..................................................... 22
1. State density functions ................................ 22
2. Filling up zones and Peierls insulator-
metal transition ....................................... 24
3. Principle of the calculation of Erelax
for a distorted chain .................................. 25
VII. Practical example: calculation of wavetunction
energy levels, orbital density function and
band filling for a regular chain of atoms ................. 26
1. Limits of variation ink ................................ 26
2. Representation of energy and the orbital
density function using N = 8 ........................... 26
3. Wavefunction forms for bonding and
antibonding states ..................................... 27
4. Generalisation regarding atomic chain
states ................................................. 30
VIII.Conclusion ................................................ 30
Chapter II: Electron and band structure ....................... 33
I. Introduction ............................................... 33
II. Going from 1-D to 3-D ...................................... 34
1. 3-D General expression of permitted
energy .................................................. 34
2. Expressions for effective mass, band size
and mobility ............................................ 35
III.3-D covalent crystal from a molecular model:
sp3 hybrid states at nodal atoms ........................... 36
1. General notes ........................................... 36
2. Independent bonds: formation of molecular
orbitals ................................................ 38
3. Coupling of molecular orbitals and band
formation ............................................... 40
IV. Band theory limts and the origin of levels
and bands from localised states ............................ 41
1. Influence of defaults on evolution of band
structure and the introduction of
'localised levels' ...................................... 41
2. The effects of electronic repulsions,
Hubbard's bands and the insulator-metal
transition .............................................. 43
3. Effect of geometrical disorder and
Anderson localisation ................................... 47
V. Conclusion ................................................. 57
Chapter III: Electron and band structures of
'perfect' organic solids ................................... 59
I. Introduction: organic solids ............................... 59
1. Context ................................................. 59
2. Generalities ............................................ 59
3. Definition of conjugated materials; an
aide-mémoire for physicians and
electricians ............................................ 62
II. Electronic structure of organic intrinsic
solids: π-conjugated polymers ............................. 63
1. Degenerate π-conjugated polymers ........................ 63
2. Band scheme for a non-degenerate n-
conjugated polymer: poly(para-phenylene) ................ 65
III.Electronic structure of organic intrinsic
solids: small molecules .................................... 68
1. Evolution of energy levels in going from
an isolated chain to a system of solid
state condensed molecules ............................... 68
2. Energy level distribution in Alq3 ....................... 69
3. Fullerene electronic levels and states................... 70
IV. Conclusion: energy levels and electron
transport .................................................. 74
Chapter IV: Electron and band structures of
'real' organic solids ......................................... 77
I. Introduction: 'real' organic solids ........................ 77
II. Lattice-charge coupling—polarons ........................... 77
1. Introduction ............................................ 77
2. Polarons ................................................ 78
3. Model of molecular crystals ............................. 79
4. Energy spectrum of small polaron ........................ 83
5. Polarons in π-conjugated polymers ....................... 85
6. How do we cross from polaron-exciton to
polaron? ................................................ 87
7. Degenerate π-conjugated polymers and
solitons ................................................ 88
III.Towards a complete band scheme ............................ 90
1. Which effects can intervene? ............................ 90
2. Complete band scheme accumulating
different possible effects .............................. 91
3. Alq3 and molecular crystals ............................. 93
IV. Conclusion ................................................. 95
Chapter V: Conduction in delocalised, localised
and polaronic states .......................................... 99
I. Introduction ............................................... 99
II. General theories of conduction in delocalised
states ................................................... 100
1. General results of conductivity in a real
crystal: limits of classical theories .................. 100
2. Electrical conduction in terms of
mobilities and the Kubo-Greenwood
relationship: reasoning in reciprocal
space and energy space for delocalised
states ................................................. 101
III.Conduction in delocalised band states:
degenerate and non-degenerate organic
solids .................................................... 103
1. Degenerate systems ..................................... 103
2. Non-degenerate systems: limits of
applicability of the conduction theory
in bands of delocalised states for
systems with large or narrow bands
mobility condition) .................................... 105
IV. Conduction in localised state bands ....................... 109
1. System 1: Non-degenerated regime;
conductivity in the tail band .......................... 110
2. System 2: degenerate regime;
conductivity in deep localised states .................. 111
V. Transport mechanisms with polarons ........................ 116
1. Displacements in small polaron bands and
displacements by hopping ............................... 116
2. Characteristics of hopping by small
polarons ............................................... 117
3. Precisions for the 'semi-classical'
theory: transition probabilities ....................... 120
4. Relationships for continuous
conductivity through polaron transport ................. 122
5. Conduction in 3D in π-conjugated
polymers ............................................... 124
VI. Other envisaged transport mechanisms ...................... 128
1. Sheng's granular metal model ........................... 128
2. Efros—Shklovskii's model from Coulombic
effects ................................................ 128
3. Conduction by hopping from site to site
in a percolation pathway ............................... 128
4. Kaiser's model for conduction in a
heterogeneous structure ................................ 129
VII.Conclusion: real behaviour ................................ 129
1. A practical guide to conducting
polymers ............................................... 129
2. Temperature dependence analysed using the
parameter w = —[(δ In ρ)/δ
In T] .................................................. 131
Chapter VI: Electron transport properties ................... 133
I. Introduction .............................................. 133
II. Basic mechanisms .......................................... 133
1. Injection levels ....................................... 133
2. Three basic mechanisms ................................. 134
III.Process A: various (emission) currents
produced by electrodes .................................... 135
1. Rectifying contact (blocking metal
insulator) ............................................. 135
2. Thermoelectronic emission (T ≠ 0; Ea=0) ................ 136
3. Field effect emission (Shottky): Ea
is 'medium intense' .................................... 136
4. Tunnelling effect emissions and
Fowler-Nordheim's equation ............................. 137
IV. Process В (simple injection): ohmic contact
and current limited by space charge ....................... 138
1. Ohmic contact (electron injection) ..................... 138
2. The space charge limited current law and
saturation current (Js) for simple
injection in insulator without traps.................... 139
3. Transitions between regimes ............................ 143
4. Insulators with traps and characteristics
of trap levels ......................................... 144
5. Expression for current density due to one
carrier type (JsP) with traps at one
discreet level (Et); effective mobility ................ 147
6. Deep level traps distributed according to
Gaussian or exponential laws ........................... 151
V. Double injection and volume controlled
current: mechanism С in Figure VI-2 ....................... 154
1. Introduction: differences in properties
of organic and inorganic solids ........................ 154
2. Fundamental equations for planar double
injection (two carrier types) when both
currents are limited by space charge:
form of resulting current JVCC (no trap
nor recombination centres) ............................. 155
3. Applications ........................................... 157
VI. The particular case of conduction by the
Poole-Frenkel effect ...................................... 159
1. Coulombic traps ........................................ 160
2. Conduction due to Poole-Frenkel effect
(as opposed to Schottky effect) ........................ 160
Chapter VII: Optical processes in molecular and
macromolecular solids ........................................ 163
I. Introduction .............................................. 163
II. Matrix effects due to insertion of atoms
with incomplete internal electronic levels ................ 164
1. Electronic configuration of transition
elements and rare earths ............................... 164
2. Incorporation of transition metals and
rare earths into dielectric or a
semiconductor matrix: effects on energy
levels ................................................. 165
3. Transitions studied for atoms with
incomplete layers inserted in a matrix ................. 167
III.Classic optical applications using
transition and rare earth elements ........................ 171
1. Electroluminescence in passive matrices ................ 171
2. Insertion into semiconductor matrix .................... 172
3. Light amplification: erbium lasers ..................... 173
IV. Molecular edifices and their general
properties ................................................ 174
1. Aide mचmoire: basic properties ......................... 174
2. Selection rule with respect to orbital
parities for systems with centre of
symmetry ............................................... 176
3. More complicated molecules: classical
examples of existing chromophores ...................... 177
V. Detailed description of the absorption and
emission processes in molecular solids .................... 179
1. Electron-lattice coupling effects during
electron transitions ................................... 179
2. Selection rules and allowed transitions ................ 180
3. Modified Jablonsky diagram and
modification of selection rules:
fluorescence and phosphorescence ....................... 181
4. Experimental results: discussion ....................... 183
VI. Excitons .................................................. 185
1. Introduction ........................................... 185
2. Wannier and charge transfer excitons ................... 186
3. Frenkel excitons ....................................... 188
4. States, energy levels and transitions in
physical dimers ........................................ 189
5. System containing an infinite number of
interacting molecules and exciton band:
Davidov displacement and breakdown ..................... 192
6. Aggregates ............................................. 194
7. Forster and Dexter mechanisms for
transfer of electron excitation energy ................. 195
Part Two: Components: OLEDs, photovoltaic cells
and electro-optical modulators
Chapter VIII:Fabrication and characterisation of
molecular and macromolecular optoelectronic
components ................................................... 201
I. Deposition methods ........................................ 201
1. Spin coating ........................................... 201
2. Vapour phase deposition ................................ 202
3. Polymerisation in the vapour phase
(VDP method) ........................................... 203
4. Film growth during vapour deposition:
benefits due to deposition assisted by
ion beams .............................................. 204
5. Comment: substrate temperature effects ................. 209
II. Fabrication methods: OLEDs and optical
guides for modulator arms ................................. 210
1. OLED fabrication ....................................... 210
2. Fabrication of modulator guides/arms
from polymers .......................................... 212
III.Photometric characterisation of organic
LEDs (OLEDs or PLEDs) ..................................... 217
1. General definitions .................................... 217
2. Internal and external fluxes and
quantum yields: emissions inside and
outside of components .................................. 221
3. Measuring luminance and yields with a
photodiode ............................................. 226
IV. Characterisation of polymer based linear
wave guides ............................................... 232
1. Measuring transversally diffused light ................. 232
2. Loss analyses using 'Cut - Back' and
'Endface Coupling' methods ............................. 233
Chapter IX: Organic structures and materials in
optoelectronic emitters ...................................... 235
I. Introduction ............................................. 235
II. How CRTs work ............................................ 235
III. Electroluminescent inorganic diodes ...................... 236
1. How they work ......................................... 236
2. Display applications .................................. 237
3. Characteristic parameters ............................. 237
4. In practical terms .................................... 238
IV. Screens based on liquid crystals ......................... 239
1. General points ......................................... 239
2. How liquid crystal displays work ....................... 240
3. LCD screen structure and the role of
polymers ............................................... 242
4. Addressing in LCD displays ............................. 243
5. Conclusion ............................................. 244
V. Plasma screens ............................................ 244
VI. Micro-point screens (field emission displays
(FED)) .................................................... 245
VII.Electroluminescent screens ................................ 246
1. General mechanism ...................................... 246
2. Available transitions in an inorganic
phosphor ............................................... 247
3. Characteristics of inorganic phosphors
from groups II-VI ...................................... 249
4. Electroluminescent think film displays:
how they work with alternating currents ................ 250
5. Electroluminescent devices operating
under direct current conditions ........................ 251
VIII.Organic (OLED) and polymer (PLED)
electroluminescent diodes ................................. 253
1. Brief history and resume ............................... 253
2. The two main developmental routes ...................... 253
3. How OLEDs function and their interest .................. 254
Chapter X: Electroluminescent organic
diodes ....................................................... 257
I. Introduction .............................................. 257
II. Comparing electronic injection and
transport models with experimental
results ................................................... 258
1. General points: properties and methods
applied to their study ................................. 258
2. Small molecules (Alq3) ................................. 259
3. Polymers ............................................... 267
III.Strategies for improving organic LEDs and
yields .................................................... 272
1. Scheme of above detailed processes ..................... 272
2. Different types of yields .............................. 273
3. Various possible strategies to improve
organic LED performances ............................... 274
IV. Adjusting electronic properties of organic
solids for electroluminescent applications ................ 276
1. A brief justification of n- and p-type
organic conductivity ................................... 276
2. The problem of equilibrating electron
and hole injection currents ............................ 277
3. Choosing materials for electrodes and
problems encountered with interfaces ................... 277
4. Confinement layers and their interest .................. 279
V. Examples of organic multi-layer structures ................ 279
1. Mono-layer structures and the origin of
their poor performance ................................. 279
2. The nature of supplementary layers ..................... 280
3. Classic examples of the effects of
specific organic layers ................................ 280
4. Treatment of the emitting zone in
contact with the anode ................................. 284
VI. Modification of optical properties of
organic solids for applications ........................... 285
1. Adjusting the emitted wavelength ....................... 285
2. Excitation energy transfer mechanisms
in films doped with fluorescent or
phosphorescent dyes .................................... 286
3. Circumnavigating selection rules:
recuperation of non-radiative triplet
excitons ............................................... 288
4. Energy transfer with rare earths and
infrared LEDs .......................................... 290
5. Microcavities .......................................... 292
6. Electron pumping and the laser effect .................. 292
VII.Applications in the field of displays:
flexible screens .......................................... 294
1. The advantages ......................................... 294
2. The problem of ageing .................................. 294
3. The specific case of white diodes ...................... 296
4. The structure of organic screens ....................... 296
5. A description of the fabrication
processes used for organic RGB pixels .................. 298
6. Emerging organic-based technologies:
flexible electronic 'pages' ............................ 304
VIII.The prospective and actual production at
2002 ...................................................... 306
IX.Conclusion ................................................ 309
X.Actual state-of-the-art and prospectives ................... 310
Chapter XI: Organic photovoltaic devices .................... 313
I. Principles and history of organic based
photovoltaics ............................................. 313
1. General points: the photovoltaic effect ................ 313
2. Initial attempts using organic
materials: the phthalocyanines ......................... 316
3. Solar cells based on pentacene doped
with iodine ............................................ 318
4. The general principle of Graetzel and
current organic solar cells ............................ 320
II. π-Conjugated materials under development
for the conversion of solar energy ........................ 321
1. Metal-Insulator-Metal structures ....................... 321
2. How bilayer hetero-structures work and
their limits ........................................... 322
3. Volume heterojunctions ................................. 325
III.Additional informations about photovoltaic
cells and organic components .............................. 328
1. Discussion about mechanisms leading to
the generation of charge carriers in
organics ............................................... 328
2. Electric circuit based on an irradiated
pn-junction; photovoltaic parameters ................... 330
3. Circuit equivalent to a solar cell ..................... 334
4. Possible limits ........................................ 336
5. Examples; routes under study and the
role of various parameters ............................. 337
6. Conclusion ............................................. 339
Chapter XII: The origin of non-linear optical
properties ................................................... 341
I. Introduction: basic equations for electro-
optical effects ........................................... 341
1. Context ................................................ 341
2. Basic equations used in non-linear
optics ................................................. 341
II. The principle of phase modulators and
organic materials ......................................... 343
1. Phase modulator ........................................ 343
2. The advantages of organic materials .................... 345
3. Examples of organic donor-acceptor non-
linear optical systems ................................. 346
4. General structure of molecules used in
non-linear optics ...................................... 348
III.The molecular optical diode ............................... 349
1. The centrosymmetric molecule ........................... 349
2. Non-centrosymmetric molecules .......................... 350
3. Conclusion ............................................. 351
IV. Phenomenological study of the Pockels
effect in donor-spacer-acceptor systems ................... 353
1. Basic configuration .................................... 353
2. Fundamental equation for a dynamic
system ................................................. 355
3. Expressions for polarisability and
susceptibility ......................................... 355
4. Expression for the indice—and the
insertion of the electro-optical
coefficient r .......................................... 356
V. Organic electro-optical modulators and
their basic design ........................................ 358
1. The principal types of electro-optical
modulators ............................................. 358
2. Figures of merit ....................................... 359
3. The various organic systems available
for use in electro-optical modulators .................. 361
VI. Techniques such as etching and polyimide
polymer structural characteristics ........................ 363
1. Paired materials: polyimide/DR 1 ....................... 363
2. Device dimensions—resorting to
lithography ............................................ 364
3. Etching ................................................ 365
4. Examples of polymer based structures ................... 367
VII.Conclusion ................................................ 368
Appendices
Appendix A-l: Atomic and molecular
orbitals ................................................... 373
I. Atomic and molecular orbitals ............................. 373
1. Atomic s- and p-orbitals ............................... 373
2. Molecular orbitals ..................................... 376
3. σ- and π-bonds ......................................... 380
II. The covalent bond and its
hybridisation ............................................. 381
1. Hybridisation of atomic orbitals ....................... 381
2. sp3 Hybridisation ...................................... 383
Appendix A-2: Representation of states in a
chain of atoms ............................................ 389
I. A chain of atoms exhibiting σ-orbital
overlapping ............................................... 389
1. σ-orbitals and a compliment to the
example of 8 atoms in a chain .......................... 389
2. General representation of states in
a chain of overlapping σ s-orbitals .................... 391
3. General representation of states in
a chain of overlapping a p-orbitals .................... 393
II. π Type overlapping of p-orbitals in a
chain of atoms: π-p- and π*-p-orbitals .................... 393
III.σ-s- and σ-p-bonds in chains of atoms ..................... 394
IV. Comments .................................................. 395
1. The Bloch function ..................................... 395
2. Expression for the effective mass
(m*) ................................................... 396
Appendix A-3: Electronic and optical
properties of fullerene-C60 in the solid
(film) state .............................................. 397
I. Electronic properties of fullerene-C60 .................... 397
II. Optical properties and observed
transitions ............................................... 401
Appendix A-4: General theory of conductivity
for a regular lattice ..................................... 403
I. Electron transport effected by an
external force and its study .............................. 403
1. Effect of force on electron movement
and reasoning within reciprocal
space .................................................. 403
2 Boltzmann's transport equation .......................... 404
II. State density function, carrier flux
and current density in the reciprocal
space ..................................................... 406
1. General expressions for fluxes of
particles .............................................. 406
2. Expressions for the state density
function ............................................... 406
3. Expression for flux .................................... 408
4. Expression for current density in
reciprocal space ....................................... 408
III.Different expressions for the current
density ................................................... 409
1. Usual expression for current
density in energy space ................................ 409
2. Studies using various examples ......................... 410
3. Expressions for mobility ............................... 412
4. The Kubo - Greenwood expression for
conductivity ........................................... 413
IV. Complementary comments .................................... 414
1. Concerning the approximation of the
effective mass and isotropic
diffusions ............................................. 414
2. General laws for changes in mobility
with temperature ....................................... 415
Appendix A-5: General theory of
conductivity in localised states .......................... 417
I. Expression for current intensity
associated with hopping transport ......................... 417
1. Transcribing transport phenomena
into equations ......................................... 417
2. Calculating the current intensity
due to hopping mechanisms .............................. 419
II. Expression for current density and
thermally activated mobility .............................. 419
1. Expression for current density
relative to transport at a
particular energy level ................................ 419
2. Generalisation of the form of Kubo-
Greenwood conductivity ................................. 420
3. Thermally activated mobility ........................... 420
III.Approximations for localised and
degenerate states ......................................... 421
Appendix A-6: Expressions for thermoelectric
power in solids: conducting polymers ...................... 423
I. Definition and reasons for use ............................ 423
1. Definition ............................................. 423
2. Reasons for use ........................................ 423
II. ТЕР of metals (EF within a band of
delocalised states) ....................................... 424
III.ТЕР of semiconductors (SC) (EF in the
gap) ...................................................... 424
1. Preliminary remark ..................................... 425
2. An ideal n-type semiconductor .......................... 425
3. An ideal n-type semiconductor .......................... 426
4. Comment on amorphous semiconductors .................... 426
5. A non-ideal amorphous semiconductor
with ЕF below its states in the
band tails ............................................. 426
IV. ТЕР under a polaronic regime .............................. 427
1. High temperature regime ................................ 427
2. Intermediate temperature regime ........................ 427
3. Other regimes .......................................... 427
V. The ТЕР for a high density of localised
states around ЕF .......................................... 427
1. Initial hypothesis ..................................... 427
2. The result in VRH ...................................... 428
VI. General representation .................................... 429
VII.Real behaviour ............................................ 429
1. General laws ........................................... 429
2. Behaviour as a function of doping
levels ................................................. 430
3. Representational graph ................................. 431
4. An example result ...................................... 431
Appendix A-7: Stages leading to emission and
injection laws at interfaces .............................. 433
I. Thermoelectric emission and the
Dushman-Richardson law .................................... 433
II. Schottky injection (field effect
emissions) ................................................ 434
1. The potential barrier at the atomic
scale .................................................. 435
2. Emission conditions: Schottky
emission law and the decrease
in the potential barrier by
field effect ........................................... 435
III.Injection through tunnelling effect
and the Fowler-Nordheim equation .......................... 437
1. The problem ............................................ 437
2. Form of the transparency (T) of a
triangular barrier ..................................... 438
3. The Fowler-Nordheim equation ........................... 440
Appendix A-8: Energy levels and permitted
transitions (and selection rules) in
isolated atoms ............................................ 443
I. Spherical atoms with an external
electron .................................................. 443
1. Energy levels and electron
configuration .......................................... 443
2. Selection rules ........................................ 444
II. An atom with more than one peripheral
electron .................................................. 445
1. First effect produced from the
perturbation Hee due to exact
electronic interactions ................................ 445
2. Perturbation involving the coupling
energy between different magnetic
moments exactly tied to kinetic
moments ................................................ 446
3. Selection rules ........................................ 447
Appendix A-9: Etching polymers with
ion beams: characteristics and results .................... 449
I. Level of pulverisation (Y) ................................ 449
1. Definition ............................................. 449
2. The result Yphysical = f(E):
3 zones ................................................ 450
3. Level of chemical pulverisation ........................ 451
II. The relationship between etching speed
and degree of pulverisation ............................... 451
1. At normal incidence .................................... 451
2. At oblique incidence ................................... 452
III.Speed of reactive etching (IBAE Ar+/02
or 0+/02).................................................. 452
IV. Preliminary modelling of Yphysical
for PI 2566 ............................................... 454
1. Levels of carbon pulverisation using
0+ ions ................................................ 454
2. Comparing simulations of
Yphysical(Θ) = f(Θ) and
the Thompson and Sigmund models ........................ 454
V. Results from etching of polyimides ........................ 455
1. Self-supporting polyimide: UPILEX ...................... 455
2. A study of the etching of PI 2566 ...................... 456
Appendix A-10: An aide-mémoire on
dielectrics ............................................... 459
I. Definitions of various dielectric
permittivities ............................................ 459
1. Absolute permittivity .................................. 459
2. Relative permittivity .................................. 459
3. Complex relative permittivity .......................... 460
4. Limited permittivities ................................. 460
5. Dielectric conductivity ................................ 461
6. Classification of diverse dielectric
phenomena .............................................. 461
II. Relaxation of a charge occupying two
position separated by a potential
barrier .................................................. 463
1. Aide-mémoire .......................................... 463
2. Transportation in a dielectric with
trapping levels, and the effect of
an electric field on transitions
between trap levels ................................... 464
3. Expression for the polarisation at
an instant t following the
displacement of electrons ............................. 466
4. Practical determination of potential
well depths ........................................... 467
Appendix A-11: The principal small
molecules and polymers used in organic
optoelectronics ........................................... 471
I. Chemical groups and electron transport .................... 471
II. Examples of polymers used for their
electroluminescence ....................................... 471
1. The principal emitting polymers ........................ 471
2. 'The' polymer for hole injection
layers (HIL) ........................................... 472
3. Example of a polymer used in hole
transport layers (HTL) ................................. 473
4. Example of a polymer used in
electron transport layer (ETL) ......................... 473
III.Small molecules ........................................... 473
1. The principal green light emitting
ligands ................................................ 473
2. Principal electron transporting small
molecules emitting green light ......................... 474
3. Example electron transporting small
molecules emitting blue light .......................... 474
4. Example small molecules which emit
red light .............................................. 474
5. Examples of small molecules which
serve principally as hole injection
layers (HIL) ........................................... 475
6. Examples of small molecules serving
principally in hole transport layers
(HTL) .................................................. 475
7. Example of a small molecule serving
principally to confine holes in 'hole
blocking layers' (HBL) ................................. 476
Appendix A-12: Mechanical generation of the
second harmonic and the Pockels effect .................... 477
I. Mechanical generation of the second
harmonic (in one-dimension) ............................... 477
1. Preliminary remark: the effect of
an intense optical field (Еω) .......................... 477
2. Placing the problem into equations ..................... 477
3. Solving the problem .................................... 480
II. Excitation using two pulses and the
Pockels effect ............................................ 481
1. Excitation from two pulses ............................. 481
2. The Pockels Effect ..................................... 482
Bibliography ................................................. 485
Index ........................................................ 495
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