Different agglomeration properties of PC61BM and PC71BM in photovoltaic inks – a spin-echo SANS study

Gabriel Bernardo; Manuel Melle-Franco; Adam L. Washington; Robert M. Dalgliesh; Fankang Li; Adélio Mendes; Steven R. Parnell

doi:10.1039/C9RA08019H

Different agglomeration properties of PC₆₁BM and PC₇₁BM in photovoltaic inks – a spin-echo SANS study†

Gabriel Bernardo,

*^a Manuel Melle-Franco,

^b Adam L. Washington,

^c Robert M. Dalgliesh,

^c Fankang Li,

^d Adélio Mendes

^a and Steven R. Parnell*^e

Author affiliations

* Corresponding authors

^a LEPABE – Laboratory for Process Engineering, Environment, Biotechnology and Energy, Faculty of Engineering, University of Porto, Rua Dr Roberto Frias, 4200-465 Porto, Portugal
E-mail: gbernardo@fe.up.pt

^b CICECO—Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal

^c ISIS Pulsed Neutron and Muon Source, STFC, Rutherford Appleton Laboratory, Harwell, Oxon, UK

^d Neutron Technologies Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA

^e Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft, Netherlands
E-mail: S.R.Parnell@tudelft.nl

Abstract

Fullerene derivatives are used in a wide range of applications including as electron acceptors in solution-processable organic photovoltaics. We report agglomeration of fullerene derivatives in optically opaque solutions of PC₆₁BM and PC₇₁BM, with concentrations ranging from 30 mg mL⁻¹ up to 90 mg mL⁻¹, in different solvents with relevance to organic photovoltaics, using a novel neutron scattering technique, Spin-Echo Small Angle Neutron Scattering (SESANS). From SESANS, agglomerates with correlation lengths larger than 1 μm are found in some PC₆₁BM solutions, in contrast no agglomerates are seen in PC₇₁BM solutions. These results clearly show that PC₇₁BM is fundamentally more soluble than PC₆₁BM in the solvents commonly used in photovoltaic inks and corroborating similar observations previously achieved using other experimental techniques. Computer models are presented to study the energetics of solution and agglomeration of both species, ascribing the difference to a kinetic effect probably related to the larger anisotropy of PC₇₁BM. Also, this work showcases the power of SESANS to probe agglomerates of fullerene derivatives in completely opaque solutions for agglomerates of the order of one to several microns.

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Article information

DOI: https://doi.org/10.1039/C9RA08019H
Article type: Paper
Submitted: 02 Oct 2019
Accepted: 10 Dec 2019
First published: 29 Jan 2020
This article is Open Access

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RSC Adv., 2020,10, 4512-4520

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Different agglomeration properties of PC₆₁BM and PC₇₁BM in photovoltaic inks – a spin-echo SANS study

G. Bernardo, M. Melle-Franco, A. L. Washington, R. M. Dalgliesh, F. Li, A. Mendes and S. R. Parnell, RSC Adv., 2020, 10, 4512 DOI: 10.1039/C9RA08019H

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