Low exciton binding energies from computational predictions de Gier, Hilde Dorothea

IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record

Publication date: 2016 Link to publication in University of Groningen/UMCG research database

Citation for published version (APA): de Gier, H. D. (2016). Low exciton binding energies from computational predictions: Towards the next generation of organic photovoltaics [Groningen]: University of Groningen

Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum.

Download date: 29-01-2017

Low exciton binding energies from computational predictions Towards the next generation of organic photovoltaics

Hilde D. de Gier

Low exciton binding energies from computational predictions Towards the next generation of organic photovoltaics Hilde D. de Gier PhD thesis University of Groningen The Netherlands Zernike Institute PhD thesis series 2016-01 ISSN: 1570-1530 ISBN: 978-90-367-8346-0 ISBN: 978-90-367-8347-7

printed version electronic version

The research presented in this thesis was performed in the research group Theoretical Chemistry of the Zernike Institute for Advanced Materials at the University of Groningen, The Netherlands. Parts of the work were carried out at the Dutch National Supercomputers Huygens and Cartesius with grants from The Netherlands eScience Center and at the Titan Supercomputer at the Oak Ridge Leadership Computing Facility (USA) through an INCITE-DD grant. This PhD project was funded by the Foundation of Fundamental Research on Matter (FOM), which is part of The Netherlands Organisation for Scientific Research (NWO). This is a publication of the FOM-focus group ‘Next Generation Organic Photovoltaics’, participating in the Dutch Institute for Fundamental Energy Research (DIFFER). © 2016 Hilde D. de Gier

Printed by Gildeprint Drukkerijen – Enschede

Low exciton binding energies from computational predictions Towards the next generation of organic photovoltaics

Proefschrift

ter verkrijging van de graad van doctor aan de Rijksuniversiteit Groningen op gezag van de rector magnificus prof. dr. E. Sterken en volgens besluit van het College voor Promoties. De openbare verdediging zal plaatsvinden op maandag 1 februari 2016 om 12.45 uur

door

Hilde Dorothea de Gier geboren op 13 mei 1988 te Dongeradeel

Promotores Prof. dr. H.B. Broer-Braam Prof. dr. J.C. Hummelen Copromotor Dr. R.W.A. Havenith Beoordelingscommissie Prof. dr. S.J. Marrink Prof. dr. A. Meijerink Prof. dr. M.A. Ratner

C’est le temps que tu as perdu pour ta rose qui fait ta rose si importante. Le Petit Prince, 1943 Antoine de Saint-Exupéry

Aan mijn grootouders Pie en Rein die met mij meegaan

Contents 1

Introduction into the field of organic photovoltaics

11

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10

11 12 15 16 19 20 22 24 26

1.11

2

Technology and energy market Operating principle Device architecture Typical donor and acceptor molecules Models for the description of electronic properties Photovoltaic process Exciton binding energy and charge-transfer exciton binding energy Proposed mechanisms for charge separation Aim and approach of the research programme Aim of the theoretical research within the programme and thesis outline References

Theory 2.1 2.2 2.3 2.4 2.5

2.6

2.7

30 31

35 Schrödinger equation Born-Oppenheimer approximation Pauli principle Hartree-Fock theory Post Hartree-Fock methods 2.5.1 Configuration interaction 2.5.2 Multiconfiguration and multireference theories 2.5.3 Møller-Plesset many-body perturbation theory 2.5.4 Coupled-cluster theory Density Functional Theory 2.6.1 Hohenberg-Kohn theorems 2.6.2 Kohn-Sham theory 2.6.3 Exchange-correlation hole 2.6.4 Approximations to the functional for the exchange-correlation energy 2.6.5 Self-interaction Time-dependent Density Functional Theory 2.7.1 Runge-Gross theorem and time-dependent Kohn-Sham equation 2.7.2 Known failures

35 36 37 37 40 40 41 41 42 43 43 45 47 47 49 49 49 50

2.8 2.9 2.10 2.11

2.12

3

Non-innocent side-chains with dipole moments in organic solar cells improve charge separation 3.1 3.2 3.3

51 52 53 54 55 55 57 57 60

65

Introduction Computational details Results and discussion 3.3.1 Geometry of the central donor-acceptor complex 3.3.2 Results for the donor-acceptor complex 1-3 3.3.3 Results for the donor-acceptor complex 2-3 Conclusions Acknowledgements References

66 69 73 73 73 75 78 78 79

Promising strategy to improve charge separation in organic photovoltaics: installing permanent dipoles in PCBM analogues

81

4.1 4.2 4.3

82 86 89

3.4 3.5 3.6

4

2.7.2.1 Charge-transfer excitations Valence Bond theory Band theory Molecular Dynamics Computational modelling of organic photovoltaics 2.11.1 Multiscale modelling 2.11.2 Modelling the molecular environment 2.11.3 Motivation for the (TD-)DFT approach applied in the studies described in this thesis References

4.4 4.5 4.6

Introduction Computational details Results and discussion 4.3.1 Comparison between experimental and calculated electronic and optical properties 4.3.2 Isotropic polarisabilities and dipole moments 4.3.3 Electronic state diagrams Conclusions Acknowledgements References

89 91 91 95 96 97

5

Influence of push-pull group substitution patterns on excited state properties of donor-acceptor co-monomers and their trimers 101 5.1 5.2 5.3

Introduction Computational details Results and discussion 5.3.1 Monomers 5.3.1.1 Geometries 5.3.1.2 Molecular orbitals 5.3.1.3 Excited state properties 5.3.1.4 Properties relevant for OPV applications 5.3.2 Trimers 5.3.2.1 Geometries 5.3.2.2 Molecular orbitals 5.3.2.3 Excited state properties 5.3.2.4 Properties relevant for OPV applications Conclusions Acknowledgements References

102 106 108 108 108 108 110 112 114 114 115 116 118 120 122 123

On the relation between local and charge-transfer exciton binding energies in organic photovoltaic materials

125

5.4 5.5 5.6

6

6.1 6.2

6.3

6.4 6.5

Introduction Computational details 6.2.1 Charge transfer and charge separation upon excitation 6.2.2 Effect of an embedding on the vertical local exciton binding energy 6.2.3 Monomer-PCBM complexes Results and discussion 6.3.1 Charge transfer and charge separation upon excitation 6.3.1.1 Monomers 6.3.1.2 Trimers 6.3.2 Effect of an embedding on the vertical local exciton binding energy 6.3.3 Monomer-PCBM complexes 6.3.3.1 Excited state properties 6.3.3.2 Charge-transfer exciton binding energies Conclusions Acknowledgements

126 131 131 133 133 134 134 134 137 140 141 141 144 145 146

6.6

7

References

147

Outlook

151

7.1 7.2 7.3 7.4

151 153 155 156

Worm’s eye view Bird’s eye view Future perspective for organic photovoltaics References

Appendix A A.1 A.2 A.3

159 Analysis of the TD-DFT (BHandH/DZP) calculations of 1-3 in vacuum, embedded in 4 and embedded in 1 Analysis of the TD-DFT (BHandH/DZP) calculations of 2-3 in vacuum, embedded in 4 and embedded in 2 Analysis of the TD-DFT (CAMYB3LYP/DZP) calculation of 1-3 in vacuum

Appendix B B.1

159 161 165

167 Analysis of the TD-DFT (BHandH/DZP) calculations of Si-CPDTBT-PCBDN in vacuum, embedded in PCBBz and embedded in PCBDN

167

Summary

171

Samenvatting

175

Curriculum Vitae

179

Acknowledgements

181