Diffusion-Limited Crystallization: A Rationale for the Thermal Stability of Non-Fullerene Solar Cells
Journal article, 2019

© 2019 American Chemical Society. Organic solar cells are thought to suffer from poor thermal stability of the active layer nanostructure, a common belief that is based on the extensive work that has been carried out on fullerene-based systems. We show that a widely studied non-fullerene acceptor, the indacenodithienothiophene-based acceptor ITIC, crystallizes in a profoundly different way as compared to fullerenes. Although fullerenes are frozen below the glass-transition temperature Tg of the photovoltaic blend, ITIC can undergo a glass-crystal transition considerably below its high Tg of ∼180 °C. Nanoscopic crystallites of a low-temperature polymorph are able to form through a diffusion-limited crystallization process. The resulting fine-grained nanostructure does not evolve further with time and hence is characterized by a high degree of thermal stability. Instead, above Tg, the low temperature polymorph melts, and micrometer-sized crystals of a high-temperature polymorph develop, enabled by more rapid diffusion and hence long-range mass transport. This leads to the same detrimental decrease in photovoltaic performance that is known to occur also in the case of fullerene-based blends. Besides explaining the superior thermal stability of non-fullerene blends at relatively high temperatures, our work introduces a new rationale for the design of bulk heterojunctions that is not based on the selection of high-Tg materials per se but diffusion-limited crystallization. The planar structure of ITIC and potentially other non-fullerene acceptors readily facilitates the desired glass-crystal transition, which constitutes a significant advantage over fullerenes, and may pave the way for truly stable organic solar cells.

organic solar cell

thermally stable photovoltaics

non-fullerene acceptor

glass-transition temperature

diffusion-limited crystallization

Author

Liyang Yu

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Christian Müller Group

Sichuan University

D. P. Qian

Linköping University

Sara Marina

Institute for Polymer Materials, San Sebastian

Ferry Nugroho

Chalmers, Physics, Chemical Physics

A. Sharma

Flinders University

University of Bordeaux

Sandra Hultmark

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Christian Müller Group

Anna Hofmann

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Christian Müller Group

Renee Kroon

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Christian Müller Group

Johannes Benduhn

Technische Universität Dresden

Detlef M. Smilgies

Cornell University

K. Vandewal

Universiteit Hasselt

Mats Andersson

Flinders University

Christoph Langhammer

Chalmers, Physics, Chemical Physics

Jaime Martín

Basque Foundation for Science (Ikerbasque)

Institute for Polymer Materials, San Sebastian

Feng Gao

Linköping University

Christian Müller

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Christian Müller Group

ACS Applied Materials & Interfaces

1944-8244 (ISSN) 1944-8252 (eISSN)

Subject Categories

Inorganic Chemistry

Materials Chemistry

Condensed Matter Physics

DOI

10.1021/acsami.9b04554

More information

Latest update

8/26/2019