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  3. Diffusion-Limited Crystallization: A Rationale for the Thermal Stability of Non-Fullerene Solar Cells

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

  • ACS Appl Mater Interfaces. 2019 Jun 19;11(24):21766-21774. doi: 10.1021/acsami.9b04554.
Liyang Yu 1,  Deping Qian 2,  Sara Marina 3,  Ferry A A Nugroho,  Anirudh Sharma 4 5,  Sandra Hultmark,  Anna I Hofmann,  Renee Kroon,  Johannes Benduhn 6,  Detlef-M Smilgies 7,  Koen Vandewal 8,  Mats R Andersson 4,  Christoph Langhammer,  Jaime Martín 3 9,  Feng Gao 2,  Christian Müller
Affiliations

Affiliations

  • 1 College of Chemistry , Sichuan University , Chengdu 610064 , P. R. China.
  • 2 Department of Physics, Chemistry and Biology (IFM) , Linköping University , SE-581 83 Linköping , Sweden.
  • 3 POLYMAT and Polymer Science and Technology Department, Faculty of Chemistry , University of the Basque Country UPV/EHU , Paseo Manuel de Lardizabal 3 , 20018 Donostia-San Sebastián , Spain.
  • 4 Flinders Institute for Nanoscale Science and Technology , Flinders University , Sturt Road , Bedford Park, Adelaide , SA 5042 , Australia.
  • 5 Laboratoire de Chimie des Polymères Organiques (LCPO) , University of Bordeaux, UMR 5629 , B8 Allée Geoffroy Saint Hilaire , 33615 Pessac Cedex , France.
  • 6 Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics , Technische Universität Dresden , Nöthnitzer Straße 61 , 01187 Dresden , Germany.
  • 7 Cornell High Energy Synchrotron Source (CHESS) , Ithaca , New York 14850 , United States.
  • 8 Institute for Materials Research (IMO-IMOMEC) , Hasselt University , Wetenschapspark 1 , 3590 Diepenbeek , Belgium.
  • 9 Ikerbasque, Basque Foundation for Science , E-48011 Bilbao , Spain.
PMID: 31185565 DOI: 10.1021/acsami.9b04554
Abstract

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.

Keywords

diffusion-limited crystallization; glass-transition temperature; non-fullerene acceptor; organic solar cell; thermally stable photovoltaics.

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