List of contributors ...................................... xi
Preface ................................................. xiii
1 Engineering colloidal quantum dots: synthesis, surface
chemistry, and self-assembly ............................... 1
Maryna I. Bodnarchuk and Maksym V. Kovalenko
1.1 Colloidal synthesis of inorganic nanocrystals and quantum
dots ....................................................... 1
1.1.1 Introductory remarks: history and terminology ....... 1
1.1.2 Basics of the surfactant-assisted colloidal
synthesis of NC quantum dots ........................ 2
1.2 Long-range ordered NC solids ............................... 7
1.2.1 Single-component NC superlattices ................... 7
1.2.2 Multicomponent NC superlattices ..................... 9
1.2.3 Shape-directed self-assembly of NCs ................ 13
1.3 Surface chemistry - a gateway to applications of NCs ...... 16
1.3.1 Organic capping ligands ............................ 16
1.3.2 Complete removal of organic ligands and inorganic
surface functionalization .......................... 19
References ................................................ 20
2 Aqueous based colloidal quantum dots for optoelectronics .. 30
Vladimir Lesnyak and Nikolai Gaponik
2.1 Introduction .............................................. 30
2.2 Aqueous colloidal synthesis of semiconductor NCs .......... 32
2.2.1 ZnXNCs ............................................. 32
2.2.2 Alloyed ZnSe based NCs ............................. 34
2.2.3 CdXNCs ............................................. 35
2.2.4 Core/shell CdTe based NCs .......................... 36
2.2.5 Alloyed CdTe based NCs ............................. 37
2.2.6 CdSe, CdSe/CdS NCs ................................ 39
2.2.7 HgX and PbX NCs .................................... 39
2.2.7.1 HgXNCs .................................... 40
2.2.7.2 PbXNCs .................................... 40
2.3 Assemblies and functional architectures of NCs ........... 41
2.3.1 LbL assembly technique ............................. 43
2.3.2 Assembly of NCs on micro-and nano-beads ............ 46
2.3.3 Covalent coupling of NCs ........................... 47
2.3.4 Controllable aggregation ........................... 48
2.3.5 Nanowires and nanosheets ........................... 49
2.3.6 Nanocrystal based gels and aerogels ................ 49
2.4 Conclusions and outlook ................................... 50
References ................................................ 51
3 Electronic structure and optical transitions in colloidal
semiconductor nanocrystals ................................ 59
Todd D. Krauss and Jeffrey J. Peterson
3.1 Introduction .............................................. 59
3.2 Foundational concepts ..................................... 60
3.3 A simple model ............................................ 65
3.4 Experimental evidence for quantum confinement ............. 67
3.5 Engineered quantum dot structures ......................... 71
3.6 Advanced theoretical treatments ........................... 73
3.7 Atomistic approaches ...................................... 76
3.8 Current challenges and future outlook ..................... 80
References ................................................ 81
4 Charge and energy transfer in polymer/nanocrystal
blends: physics and devices ............................... 87
Kevin M. Noone and David S. Ginger
4.1 Introduction .............................................. 87
4.2 A brief history of QD/polymer optoelectronics ............. 88
4.2.1 Quantum dot light emitting diodes (QD-LEDs) -
size-tunable emission across the spectrum .......... 88
4.2.2 Quantum dot photovoltaics (QD-PV) and
photodetectors - converting photons to
electrons .......................................... 90
4.2.2.1 QD-PVs .................................... 90
4.2.2.2 Quantum dot photodetectors ................ 93
4.3 The QD-organic interface - ligands and more ............... 96
4.3.1 Ligands ............................................ 96
4.3.2 Energetics ......................................... 98
4.3.2.1 Charge transfer and Forster resonance
energy transfer (FRET) in QD-LEDs ......... 99
4.3.2.2 Type II heterojunctions and charge
transfer in QD-PVs ........................ 99
4.4 Conclusion and future outlook ............................ 104
References ............................................... 105
5 Multiple exciton generation in semiconductor quantum
dots and electronically coupled quantum dot arrays for
application to third-generation photovoltaic solar
cells .................................................... 112
Matthew C. Beard, Joey M. Luther, and Arthur J. Nozik
5.1 Introduction ............................................. 112
5.2 Relaxation dynamics of photogenerated electron-hole
pairs in QDs ............................................. 115
5.2.1 Transient absorption spectroscopy (ТА) ............ 117
5.3 Multiple exciton generation (MEG) ........................ 121
5.3.1 MEG in QDs ........................................ 121
5.3.2 MEG controversy and role of photocharging ......... 125
5.3.3 MEG efficiency and comparison to impact
ionization in bulk semiconductors ................. 128
5.4 QD solar cells ........................................... 131
5.4.1 MEG photocurrent and determination of the
internal quantum efficiency (IQE) in QD solar
cells ............................................. 133
5.5 QD arrays ................................................ 136
5.5.1 MEG in PbSe QD arrays ............................ 137
5.6 Conclusions .............................................. 140
References ............................................... 141
6 Colloidal quantum dot light emitting devices ............. 148
Vanessa Wood, Matthew Panzer, Seth-Coe Sullivan, and
Vladimir Bulovic
6.1 Introduction ............................................. 148
6.2 Why QDs for LEDs? ........................................ 148
6.2.1 Saturated colors .................................. 148
6.2.2 Solution processable .............................. 150
6.2.3 Stability ......................................... 150
6.3 QD and device physics influencing LED performance ........ 151
6.3.1 Quantifying the luminescence efficiency ........... 151
6.3.2 QD surface states ................................. 152
6.3.3 QD charging ....................................... 153
6.3.4 Charge transport in QD films ...................... 154
6.3.5 Field driven luminescence quenching ............... 154
6.3.6 Isolating the effects of charge and field ......... 155
6.4 Characterizing QD-LEDs ................................... 157
6.5 QD-LEDs based on optical downconversion .................. 160
6.6 QD-LEDs based on organic charge transport layers ......... 161
6.6.1 Deposition of QDs: spin casting, phase
separation, and microcontact printing ............. 161
6.6.2 Operation of colloidal QD-LEDs .................... 163
6.7 QD-LEDs with inorganic charge transport layers ........... 165
6.7.1 Reasons for inorganic charge transport layers ..... 165
6.7.2 Fabrication of all inorganic QD-LEDs .............. 165
6.7.3 Operation of QD-LED with inorganic charge
transport layers .................................. 166
6.7.4 Improving the efficiency of QD-LEDs with
inorganic charge transport layers ................. 167
6.8 Future work .............................................. 167
References ............................................... 168
7 Colloidal quantum dot photodetectors ..................... 173
Gerasimos Konstantatos
7.1 Introduction ............................................. 173
7.1.1 Applications of top-surface photodetectors ........ 173
7.1.2 Colloidal quantum dots (CQDs) for light
detection ......................................... 174
7.2 Fundamentals of photodetectors ........................... 175
7.2.1 Types of photodetectors ........................... 175
7.2.2 Figures of merit .................................. 176
7.3 Prior art in solution-processed photodetectors ........... 177
7.4 Solution-processed QD photoconductors .................... 179
7.4.1 Photoconductive gain and noise in PbS QD
photodetectors .................................... 179
7.4.2 Visible-wavelength and multispectral
photodetection .................................... 183
7.4.3 Control of temporal response in photoconductive
detectors via trap state engineering .............. 185
7.5 CQD based phototransistors ............................... 187
7.6 CQD photodiodes .......................................... 190
7.7 Conclusions - summary .................................... 193
References ............................................... 195
8 Optical gain and lasing in colloidal quantum dots ........ 199
Sjoerd Hoogland
8.1 Introduction ............................................. 199
8.2 Optical properties of colloidal nanocrystal quantum
dots ..................................................... 200
8.3 Carrier dynamics in colloidal quantum dots ............... 202
8.3.1 Auger recombination ............................... 205
8.3.2 Poisson statistics and state filling .............. 206
8.4 Gain in solid state nanocrystal quantum dot films ........ 207
8.4.1 Amplified spontaneous emission (ASE) .............. 208
8.4.2 Variable strip length (VSL) for optical gain
measurements ...................................... 209
8.4.3 Experimental techniques for waveguide loss
measurement in colloidal quantum dot films ........ 209
8.4.4 Modal gain in visible colloidal quantum dots
based on cadmium chalcogenides .................... 211
8.4.5 Modal gain in infrared colloidal quantum dots
based on lead chalcogenides ....................... 213
8.5 Spectral and temporal characteristics of optical gain
in nanocrystal quantum dots .............................. 214
8.5.1 Visible colloidal quantum dots based on cadmium
chalcogenides ..................................... 214
8.5.2 Infrared colloidal quantum dots based on lead
chalcogenides ..................................... 218
8.6 Colloidal nanocrystal lasers ............................. 221
8.6.1 Microcapillary resonators ......................... 223
8.6.2 Microsphere resonators ............................ 224
8.6.3 Distributed feedback resonators ................... 225
8.6.4 Microtoroid resonators ............................ 225
8.6.5 Other resonators .................................. 226
8.7 Future prospects ......................................... 226
8.7.1 Single exciton gain ............................... 226
References ............................................... 229
9 Heterojunction solar cells based on colloidal quantum
dots ..................................................... 233
Jeffrey J. Urban and Delia J. Milliron
9.1 Introduction ............................................. 233
9.2 Chemistry of CQDs for solar cells ........................ 234
9.3 Physics of CQDs for solar cells .......................... 238
9.3.1 Electronic structure evolution in low
dimensional systems ............................... 238
9.3.2 Fundamentals of light-matter interactions in QDs .. 240
9.3.3 Selection rules and the complications of Я ........ 241
9.4 Optical and electronic properties of CQD films for
solar cells .............................................. 241
9.5 Device physics and design of CQD heterojunction solar
cells .................................................... 246
9.6 Technology and scientific outlook ........................ 250
References ............................................... 251
10 Solution-processed infrared quantum dot solar cells ...... 256
Jiang Tang and Edward H. Sargent
10.1 Introduction ............................................. 256
10.2 Infrared CQDs for the full absorption of solar spectrum .. 257
10.2.1 Bandgap engineering for the broadband solar
spectrum match .................................... 257
10.2.2 Light absorption in CQD film ...................... 260
10.3 Semiconductor solar cell fundamentals .................... 260
10.3.1 Fundamentals of p-n junction ...................... 260
10.3.2 Fundamentals of solar cells ....................... 263
10.3.3 Implications for CQD solar cell optimization ...... 264
10.4 Electrical properties of CQD films ....................... 265
10.4.1 Measurements of electrical properties of CQD
films ............................................. 265
10.4.2 Transport in CQD film ............................. 269
10.4.3 CQD passivation ................................... 272
10.4.4 CQD film doping ................................... 275
10.4.5 Dielectric constant of CQD film ................... 276
10.5 Progress in CQD solar cell performance ................... 276
10.5.1 Schottky solar cells .............................. 276
10.5.2 Heterojunction solar cells ........................ 279
10.6 Device stability ......................................... 283
10.7 Perspectives and conclusions ............................. 285
References ............................................... 286
11 Semiconductor quantum dot sensitized TiO2 mesoporous
solar cells .............................................. 292
Lioz Etgar, Hyo Joong Lee, Sang II Seok,
Md.K. Nazeeruddin, and Michael Grätzel
11.1 Introduction ............................................. 292
11.2 Mesoscopic PbS quantum dot/TiO2 heterojunction solar
cells .................................................... 294
11.2.1 Solid-state PbS/TiO2 heterojunction solar cell .... 299
11.3 QD/TiO2 mesoporous solar cell using the SILAR process .... 301
11.4 Cobalt complex-based redox couples in CQD-TiO2
mesoporous solar cells ................................... 305
References ............................................... 308
Index .................................................... 310
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