Table Of ContentUnconventional Thin Film Photovoltaics
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RSC Energy and Environment Series
Editor-in-Chief:
Professor Laurence M. Peter, University of Bath, UK
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F Dr Heinz Frei, Lawrence Berkeley National Laboratory, USA
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6 Dr Roberto Rinaldi, Max Planck Institute for Coal Research, Germany
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2 Professor Tim S. Zhao, The Hong Kong University of Science and Technology,
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8 Hong Kong, China
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9/ Titles in the Series:
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1 1: Thermochemical Conversion of Biomass to Liquid Fuels and Chemicals
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oi:1 2: Innovations in Fuel Cell Technologies
d 3: Energy Crops
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or 4: Chemical and Biochemical Catalysis for Next Generation Biofuels
sc. 5: Molecular Solar Fuels
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htt 8: Solar Energy Conversion: Dynamics of Interfacial Electron and
on Excitation Transfer
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1 9: Photoelectrochemical Water Splitting: Materials, Processes
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e and Architectures
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n 1 Explorations from Natural Utilization Systems
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sh 12: Materials Challenges: Inorganic Photovoltaic Solar Energy
ubli 13: Catalytic Hydrogenation for Biomass Valorization
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14: Photocatalysis: Fundamentals and Perspectives
15: Photocatalysis: Applications
16: Unconventional Thin Film Photovoltaics
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Unconventional Thin Film
Photovoltaics
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40 Edited by
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1 Enrico Da Como
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9/9 University of Bath, UK
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doi: Filippo De Angelis
org | CNR Institute of Molecular Sciences and Technologies, Perugia, Italy
sc. Email: [email protected]
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htt University of Oxford, UK
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c.or PDFeISBN:978-1-78262-406-6
s.rs EPUBeISBN:978-1-78262-824-8
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he Act1988andtheCopyrightandRelatedRightsRegulations2003,thispublicationmaynot
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F Preface
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0.1 By the end of 2014, almost 50% of the world’s photovoltaic (PV) capacity of
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g | d 38 GWp. The exponential growth of PV has continued in spite of the world-
or wide economic recession. China is now catching up rapidly and even the
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s.rs UK, which has traditionally taken a conservative view of PV, has seen an
pub astonishing burst of activity, with the installed capacity exceeding 8GWp by
p:// thesecondquarterof2015.ThevastmajorityofPVinstallationsisbasedon
htt highly developed first generation silicon technology. With efficiencies of
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01 thirdsofthetheoreticallimit,settingthetargetthatmustbematchedbyany
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e alternative PV technology. However, silicon has the drawback that its
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n footprint of the technology. An important factor in this respect is the
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s of solar cell) needed to absorb sunlight efficiently. Because silicon is an
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therefore,thetypicalthicknessofthesiliconabsorberlayerisoftheorderof
200 microns. The search for alternatives to silicon has generated second
generation technologies based on thin film solar cells that utilise semi-
conductors such as cadmium telluride (CdTe) or copper indium gallium
selenide(CIGS).Thesearedirectbandgapsemiconductorsthatabsorblight
much more efficiently than silicon, so that the absorber layers only need
to be a few microns thick. All of these technologies could be called ‘con-
ventional’ in the sense that they have all progressed from lab bench to
manufacture. By contrast, this book is concerned with newer types of
photovoltaic cells that utilise what may loosely be called ‘soft’ materials,
either organic compounds such as polymers and larger single molecules
or the interesting class of hybrid perovskite materials such as
RSCEnergyandEnvironmentSeriesNo.16
UnconventionalThinFilmPhotovoltaics
EditedbyEnricoDaComo,FilippoDeAngelis,HenrySnaithandAlisonWalker
rTheRoyalSocietyofChemistry2016
PublishedbytheRoyalSocietyofChemistry,www.rsc.org
v
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vi Preface
methylammonium lead tri-iodide (MAPbI ). As the title of this book
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indicates,thesesolarcellscanbeconsideredtobeunconventionalinsofar
as they are based on emerging types of materials that differ from
conventional inorganic semiconductors. The field of unconventional PV is
developing very rapidly, and the editors are to be congratulated for having
05 managedtobringtogethersomeofthebestknownspecialistsinthefieldsof
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66- state of the art, both from an experimental and from a theoretical stand-
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24 point. These areas of research continue to attract some of our brightest
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82 minds, and the breadth of activity illustrated by this book underlines
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81 the huge importance of PV research in the context of the challenges that
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9/9 mankind faces as a consequence of its thirst for energy.
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0 Thechaptersinthisbookareintendedtopresentabalancedcombination
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10. of in-depth explorations of the experimental and theoretical aspects of the
oi: subject,allowingthereadertogainadeeperunderstandingofthetwomain
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g | types of unconventional photovoltaic cells: hybrid organolead halide per-
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c. ovskitecellsandorganicphotovoltaics(OPV).Thelistofauthorsmayappear
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s.r rather ‘eurocentric’, but this reflects in part the fact that recent research in
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http:// butionshavealsobeenmadebygroupsinAsiaandUSA.Inparticular,inthe
n case of hybrid perovskites, pioneering studies on their use as sensitizers in
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6 mesoporous solar cells have been carried out in Tokyo and Seoul(Tsutomu
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2 MiyasakaandNam-GyuPark,respectively).Thesubsequentdevelopmentof
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14 took place essentially simultaneously in labs in Lausanne (Michael Gr¨atzel)
on and Oxford (Henry Snaith).
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he Thefirstpartofthebookprovidesanexcellentoverviewofcurrentactivity
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bli in the area of hybrid perovskites. Many aspects of the behaviour of these
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variety of different explanations suggested for the hysteretic behaviour and
apparent ferroelectric properties, to give just two examples. The jury is still
out on the validity of these explanations, but the ideas presented in this
volumecertainlyrepresentausefulstepforward.Theimportanceofsolution
processing methods and nanostructuring for achieving high performance
in hybrid perovskite cells will be evident from chapter 1 (Park) and chapter
2 (DoCampo et al.), whereas chapter 3 (Bisquert et al.) and chapter 4
(Petrozzaetal.)focusoncharacterizationmethodsandonthephotophysical
processes that determine cell performance. Chapters 6 (Yan et al.), 7 (Even
etal.),8(DeAngelisetal.)and9(WalkerandRichardson)illustratethewide
rangeaswellastheextraordinarysophisticationofcurrenttheoreticalwork
on hybrid perovskites. The theme of nanostructuring contacts, in this case
for OPV devices, is addressed in chapter 5 (Schmidt-Mende and Dorman),
andtheOPVthemeisthefocusofthechaptersinthelatterpartofthebook,
whichdealwithdifferentkindsoftheoreticalapproachestounderstandthe
physicsofOPV.Leoetal.giveanauthoritativereviewofsmallmoleculeOPV
in chapter 10 and, in chapter 11, Beljonne et al. provide an excellent status
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Preface vii
assessment and identify the key issues facing OPV. In chapter 12, Zannoni
and Roscioni describe molecular dynamics simulations and show how they
canbeappliedtothinfilms,whereasKosteretal.addresstheproblemof3-D
simulations of organic systems in chapter 13. The final chapter by Michels
and Schaefer shows how modelling can be used to unravel the complex
05 processes that take place during solution processing of OPV devices
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66- separation are key issues.
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24 Iwould liketo thank theauthors who have contributedto thisbook, and
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82 Iamalso grateful to the four editors who have guidedthe process from the
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81 outset. All have taken time from their busy schedules to put together a
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9/9 book that I hope will be an important landmark that will help propel
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1 Perovskite Solar Cells 1
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Acknowledgements 29
References 29
Chapter 2 Towards Optimum Solution-processed Planar
Heterojunction Perovskite Solar Cells 32
Fabian Hanusch, Michiel Petrus and Pablo Docampo
2.1 Introduction 32
2.2 Towards Optimum Solution-processed Cells 33
2.2.1 Basic Cell Structure 33
RSCEnergyandEnvironmentSeriesNo.16
UnconventionalThinFilmPhotovoltaics
EditedbyEnricoDaComo,FilippoDeAngelis,HenrySnaithandAlisonWalker
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x Contents
2.2.2 Towards 100% Surface Coverage 34
2.2.3 Contact Materials 43
2.3 Outlook and Conclusions 48
References 51
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2 and Organic Solar Cells 57
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78 Juan Bisquert, Germa` Garcia-Belmonte and Ivan Mora-Sero
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A Mott–Schottky Analysis 79
3.4.4 Electrode Capacitance 80
3.4.5 Dependence of Capacitance on
Illumination 81
3.5 Carrier Transport 86
3.6 Recombination in Organic Solar Cells 90
3.6.1 Recombination Mechanisms 90
3.6.2 Determination of Recombination Kinetics 91
3.7 Recombination in Perovskite Solar Cells 93
3.7.1 Radiative Recombination Coefficient
of MAPbI 93
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3.7.2 Radiative and Non-radiative Recombination
in Perovskite Solar Cells 95
3.8 Conclusions 100
Acknowledgements 101
References 101
