University of Groningen. Photophysics of nanomaterials for opto-electronic applications Kahmann, Simon

Transcription

1 University of Groningen Photophysics of nanomaterials for opto-electronic applications Kahmann, Simon 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: 2018 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Kahmann, S. (2018). Photophysics of nanomaterials for opto-electronic applications. [Groningen]: Rijksuniversiteit 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): For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date:

2 A Thesis submitted for the degree of Doctor of Philosophy Photophysics of nanomaterials for opto-electronic applications Simon Kahmann November 8, 2017 University of Groningen Friedrich-Alexander Universität Erlangen-Nürnberg

3

4 CONTENTS Contents 1 Introduction 1 2 Materials Nanoscale Semiconductors Organic Semiconductors Conjugated Polymers Interaction with Light Excited States in Organic Solids Carrier Transport in Disordered Systems Charge Generation Carbon Nanotubes Opto-electronic properties Single Walled Carbon Nanotube Spectroscopy Sorting and Selecting Carbon Nanotubes Colloidal Quantum Dots Physical Properties Lead Sulphide Colloidal Quantum Dots Colloidal Quantum Dot Solids Surface Chemistry Experimental Techniques for Optical Spectroscopy FTIR spectroscopy Measurement Principle and Advantages Fourier Transformation Photoluminescence Spectroscopy Principle Ultrafast Techniques Photoinduced Absorption Spectroscopy Basic Principle Steady State Photoinduced Absorption Spectroscopy Transient Absorption Spectroscopy i

5 PHOTOPHYSICS OF NANOMATERIALS FOR OPTO-ELECTRONICS CONTENTS 4 Monitoring Polarons in Narrow Band Gap Polymers Introduction Results and discussion Conclusion Methods Working Mechanism of Ternary Organic Solar Cells Introduction Results and Discussion Conclusion Methods Hybrid Excited States in Polymer Wrapped CNTs Introduction Results and Discussion Conclusion Methods Charge Transfer between Polymers and CQDs Introduction Results and Discussion Conclusion Methods Trap States in Lead Sulphide Colloidal Quantum Dots Introduction Results and discussion Conclusion Methods Summary and Outlook 127 Sammenvatting 130 Appendix 132 Symbols and Abbreviations 141 List of Publications 147 Acknowledgements 148 ii Simon Kahmann

6 LIST OF FIGURES List of Figures 2.1 Semiconductor density of states with respect to dimensionality Hybridisation of atomic orbitals in carbon Molecular orbitals and their energy levels Overview of different semiconducting polymers Energy levels of donor-acceptor polymers Jablsonski scheme Frank-Condon principle and vibronic side peaks Wannier-Mott and Frenkel excitons in semiconductors Polaron stabilistion mechanisms Polaron energy levels and optically allowed transitions Energy levels in different states of condensed matter Mechanisms for exciton migration Exciton motion through a Gaussian distribution of states Charge transfer state formation and dissociation CNT chirality indices and lattice vectors from graphene Construction of the CNT band dispersion DOS and band gap of metallic and semiconducting CNTs Optically allowed and forbidden transitions in CNTs Excited many body states reported for CNTs Absorption- and 2D-PL spectrum of CNTs Energy gap for PbS CQDs with respect to their size Impact of disorder and coupling on the transport in CQD solids Surface chemistry of PbS CQDs Main components of a Michelson interferometer Explanation of the Fourier transformation Illustration of the transient PL set-up Measurement principle and signals in PIA spectroscopy Steady state set-ups for PIA spectroscopy Transient absorption spectroscopy set-up Optically allowed transitions for differently charged polymers iii

7 PHOTOPHYSICS OF NANOMATERIALS FOR OPTO-ELECTRONICS LIST OF FIGURES 4.2 Absorbance and PIA spectra of C-/Si-PCPDTBT Calculated absorption spectra for C-/Si-PCPDTBT oligomers Electron-hole density of a PCPDTBT oligomer and aggregate Explanation of polymer IRAVs in the MIR spectral region Different exciation PIA spectra of neat polymers Materials and solar cell characterisation for the ternary device PL spectra of neat and blended organic films PL spectra for polymer blends of different concentration Steady state PIA spectra of the organic blends Energy levels and absorption spectra of polymer wrapped CNTs Photoluminescence spectra of polymer wrapped CNTs NIR PIA and TA of polymer wrapped CNTs MIR PIA of polymer wrapped CNTs Calculated first excitation for a polymer wrapped CNT Representative molecular orbitals for P3DDT wrapped CNTs Energy levels and absorption spectra of PbS CQDs and PCPDTBT PL spectra of neat and blended films of PCPDTBT and PbS CQDs TA and EQE of neat and blended films of PCPDTBT and PbS J-V curves of fabricated solar cells and AFM images of their ALs Sketch and TEM images of employed ligands and CQDs Absorbance spectra of CQDs in solution and as a film PIA spectra of PbS CQDs with different size and ligands PL upon ligand variation and TEM image of degraded CQDs Data ffor degradaed or differently washed PbS_OA Vibrational spectra and Fano calculations for PbS CQDs A1 Additonal electrical charactersation of organic solar cells A2 PL spectra of PDCBT:PC 70 BM A3 Absorption spectra of PF12-related samples A4 MIR PIA spectra of neat P3DDT A5 PIA spectra of a P3DDT:PCBM blend with different energy A6 PIA spectra of P3DDT wrapped CNTs A7 PIA spectra of P3DDT wrapped CNTs with excess polymer A8 PIA spectra of neat PF12 upon above and below gap excitation A9 PIA spectra of a PF12:PCBM blend A10 PIA spectra of PF12 wrapped CNTs iv Simon Kahmann

8 LIST OF TABLES List of Tables 2.1 Exciton Bohr radii of relevant semiconductors Electrical parameters of organic solar cells Extracted PL lifetimes for organic films Extracted PL lifetimes for polymer blends PL lifetimes of hybrid blends A1 Calculated transition energies for PCPDTBT aggregates A2 Calculated transition energies for trions in CNTs A3 Composition of excited states for P3DDT wrapped CNTs A4 Peak positions and widts of PIA bands of Pbs CQDs A5 Molecular vibrations associated with oleic acid A6 Molecular vibrations associated with 1,4-benzenedithiol v

9