Influence of Order and Disorder on the Photogeneration of Charge Carriers

• Applicants: Dr. Wichard Johann Daniel Beenken; Privatdozent Dr. Harald Hoppe; Professor Dr. Frédéric Laquai
• Subject Area: Experimental Condensed Matter Physics ; Organic Molecular Chemistry - Synthesis and Characterisation ; Theoretical Condensed Matter Physics
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 255377421

• Final Report Year: 2020

Final Report Abstract

The completed project provides an improved understanding on the impact of organic semiconductor order, induced by either molecular building blocks or by blending and processing induced aggregation, on charge generation and recombination. The optimized and customized selective syntheses of double dissymmetric functionalized phenylene building blocks offer great potential for the realization of elaborate side chain configurations, resulting in well-controlled induction of order along the backbone of such polymers and in potential π-stacks. Anthracene-containing poly(arylene ethynylene)-alt-poly(phenylene vinylene)s with individual side chain sequences – highly defined, partly defined and random – were produced and investigated spectroscopically. The comprehensive spectral UV-vis absorption and PL characteristics of the numerous polymer sample sets, in solution and in film, allowed the verification of side chain combination- and succession-specific structure–property relationships. The impact of the distribution of branched (2-ethylhexyloxy) and linear side chains (octyloxy) on optical and opto-electronic properties of AnE-PVs and photovoltaic devices made thereof was further elucidated. With various polymer samples quite extensive possibilities to fine-tune material characteristics, such as photophysical response, by elaborate side chain engineering were demonstrated. We further confirmed by theoretical calculation that an order-disorder control by substituting straight with branched sidechains is possible and results either in polymer-polymer stacking for more straight and polymer-fullerene intercalation for more branched sidechains. The latter results in low photovoltaic performance for low mobility of electrons along the intercalated fullerenes due to insufficient molecular orbital overlap. We experimentally demonstrated that the order of organic semiconductors could be tuned via ternary blending of ordered- and disordered-donor representatives with a fullerene acceptor, and that the state of order directly impacts on energy levels at the heterojunction relevant for charge generation and recombination. The investigations were extended for application of novel non-fullerene-acceptors, which indicated a stronger dependence of charge generation on the formation of the donor-acceptor interface morphology.

Publications

• Density Functional Study of Stacking Structure and Electronic Behaviors of AnE-PV Copolymer, J. Phys. Chem. B 2016, 120, 10854-10859
  Dong C.-D.; Beenken C.
  
• Effect of Side Chains on Molecular Conformation of Anthracene-Ethynylene-Phenylene-Vinylene Oligomers: A Comparative Density Functional Study with and Without Dispersion Interaction, J. Phys. Chem. A 2016, 120, 3835
  Dong C.-D.; Hoppe H., Beenken C.
  
• Locally resolved large phase separation in polymer fullerene blends, J. Mater. Chem. A 2016, 4, 1244-1250
  Kästner, C.; Seeland, M.; Egbe, D. A. M.; Hoppe, H.
  
• Density Functional Study on the Intercalation of Fullerene into AnE- PV Co-polymer Layers, J. Phys. Chem. B 2017, 121, 2202-2206
  Dong C.-D.; Beenken C.
  
• Revelation of interfacial energetics in organic multi-heterojunctions, Adv. Sci. 2017, 4, 1600331
  Kästner, C.; Vandewal, K.; Egbe, D. A. M.; Hoppe, H.
  
• Controlling donor crystallinity and phase separation in bulk heterojunction solar cells by the introduction of orthogonal solvent additives, MRS Adv. 2018, 3 (33), 1891- 1900
  Alam, S.; Meitzner, R.; Kaestner, C.; Ulbricht, C.; Höppener, S.; Egbe, D. A. M.; Schubert, U. S.; Hoppe, H.
  
• Improvement of polymer: Fullerene bulk heterojunction morphology via temperature and anti-solvent effect, Synth. Met. 2018, 243, 8-16
  Hleli, E.; Alam, S.; Saaidia, A.; Kästner, C.; Höppener, S.; Ulbricht, C.; Romdhane, S.; Ben Fredj, A.; Egbe, D. A. M.; Schubert, U. S.; Bouchriha, H.; Hoppe, H.
  
• Organic solar cells based on anthracene-containing PPE–PPVs and non-fullerene acceptors, Chem. Pap. 2018, 72, 1769-1779
  Alam, S.; Meitzner, R., Nwadiaru, O. V.; Friebe, C.; Cann, J.; Ahner, J.; Ulbricht, C.; Kan, Z.; Höppener, S.; Hager, M. D.; Egbe, D. A. M.; Welch, G. C.; Laquai, F.; Schubert, U. S.; Hoppe, H.
  
• Temperature-Tuning of Optical Properties and Molecular Aggregation in AnE-PVstat Copolymer Solution, J. Phys. Chem. C 2018, 122, 3965-3969
  Saaidia, A.; Saidani, M. A.; Hleli, E.; Alam, S.; Ulbricht, C.; Romdhane, S.; Fredj, A. B.; Kästner, C.; Egbe, D. A. M.; Schubert, U. S.; Bouchrina, H.; Hoppe, H.