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.
diffusion-limited crystallization
non-fullerene acceptor
thermally stable photovoltaics
glass-transition temperature
organic solar cell
Author
Liyang Yu
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry
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
Anna Hofmann
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry
Renee Kroon
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry
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
Institute for Polymer Materials, San Sebastian
Basque Foundation for Science (Ikerbasque)
Feng Gao
Linköping University
Christian Müller
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry
ACS Applied Materials & Interfaces
1944-8244 (ISSN) 1944-8252 (eISSN)
Vol. 11Subject Categories
Inorganic Chemistry
Materials Chemistry
Condensed Matter Physics
Areas of Advance
Nanoscience and Nanotechnology
Materials Science
Infrastructure
Chalmers Materials Analysis Laboratory
Nanofabrication Laboratory
DOI
10.1021/acsami.9b04554