Substrate-driven switchable molecular orientation in bulk heterojunction films identified using infrared reflection absorption spectroscopy

Shahiduzzaman, Md.; Hirayama, Tomoki; Chikamatsu, Tatsuki; Koganezawa, Tomoyuki; Nakano, Masahiro; Miyadera, Tetsuhiko; Karakawa, Makoto; Takahashi, Kohshin; Taima, Tetsuya

doi:10.1039/c9me00165d

Cited by 6 publications

(12 citation statements)

References 35 publications

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“…graphite) to weakly ( e.g. silica) interacting substrate has been shown experimentally 19,45,47,52–56 and computationally 46 to influence the orientation at the solid interface for a range of OSCs. Fig.…”

Section: Resultsmentioning

confidence: 95%

“…45–50 In general, the orientation at the solid interface depends on both the strength and anisotropy of the fluid–substrate interactions, 44 and the strength of the fluid–fluid interactions. 51 A number of experimental studies report control of orientation at this interface for specific small molecules, 19,45,47,52–56 and the strength of the interactions with the substrate has been shown to directly influence the orientation, again for a specific set of interaction parameters. 46…”

Section: Introductionmentioning

confidence: 99%

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A simple predictor of interface orientation of fluids of disk-like anisotropic particles and its implications for organic semiconductors

Boehm

Huang

2022

Soft Matter

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Section: Resultsmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

A simple predictor of interface orientation of fluids of disk-like anisotropic particles and its implications for organic semiconductors

Boehm

Huang

2022

Soft Matter

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“…graphite) to weakly (e.g. silica) interacting substrate has been shown experimentally 19,44,46,[51][52][53][54][55] and computationally 45 to influence the orientation at the solid interface for a range of OSCs. Fig.…”

Section: Solid Interfacementioning

confidence: 99%

“…There are many examples in the literature of this behaviour. 19,[44][45][46][52][53][54][55] Choosing a substrate that interacts favourably with either OSC backbone or side-chains would also be an effective means of tuning the orientation at this interface.…”

Section: Guidelines For Controlling Osc Interface Orientationmentioning

confidence: 99%

“…[44][45][46][47][48][49] In general, the orientation at the solid interface depends on both the strength and anisotropy of the fluid-substrate interactions, 43 and the strength of the fluid-fluid interactions. 50 A number of experimental studies report control of orientation at this interface for specific small molecules, 19,44,46,[51][52][53][54][55] and the strength of the interactions with the substrate has been shown to directly influence the orientation, again for a specific set of interaction parameters. 45 An interesting illustration of the contrasting behaviour of hard particles at solid and vapour interfaces is the case of a penetrable wall, from which a particle's centre-of-mass is repelled but which the rest of the molecule can penetrate to varying degrees.…”

Section: Introductionmentioning

confidence: 99%

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A simple predictor of interface orientation of mesogenic fluids and its implications for organic semiconductors

Boehm

Huang

2022

Preprint

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From classical molecular dynamics simulations, we identify a simple and general predictor of molecular orientation at solid and vapour interfaces of isotropic fluids of anisotropic particles based on their shape and interaction anisotropy. For a wide variety of inter-particle interactions, temperatures, and substrate types within the range of typical organic semiconductors and their processing conditions, we find remarkable universal scaling of the orientation at the interface with the free energy calculated from pair interactions between close-packed nearest neighbours and an empirically derived universal relationship between the entropy and the shape anisotropy and bulk volume fraction of the fluid particles. The face-on orientation of fluid particles at the solid interface is generally predicted to be the equilibrium structure, although the alignment can be controlled by tuning the particle shape and substrate type, while changing the strength of fluid--fluid interactions is likely to play a less effective role. At the vapour interface, only the side-on structure is predicted, and conditions for which the face-on structure may be preferred, such as low temperature, low interaction anisotropy, or low shape anisotropy, are likely to result in little orientation preference (due to the low anisotropy) or be associated with a phase transition to an anisotropic bulk phase for systems with interactions in the range of typical organic semiconductors. Based on these results, we propose a set of guidelines for the rational design and processing of organic semiconductors to achieve a target orientation at a solid or vapour interface.

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Switchable Crystal Phase and Orientation of Evaporated Zinc Phthalocyanine Films for Efficient Organic Photovoltaics

et al. 2020

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In photovoltaic cells, increasing the light absorption coefficient enhances the photocurrent and quantum efficiency of the cell. Here, we report an efficient approach that enhances light absorption by changing the crystal phase of an evaporated ZnPc film on indium tin oxide (ITO) substrates. Under thermal treatment (>200 °C), the crystal phase of ZnPc changed from metastable α-ZnPc to stable β-ZnPc. We tested and compared the effects of this phase transition on the donor film of organic photovoltaic (OPV) cells. After treating the β-ZnPc film at 220 °C, the short-circuit current of the OPV was improved from 2.58 to 3.40 mA/cm2, and the quantum efficiency was improved from 650 to 750 nm. Moreover, on a copper iodide (CuI)–ITO substrate, the ZnPc molecules were precisely controlled in the lying-down orientation. With their lying-down orientations, the light absorbance capacities of the metastable α-ZnPc phase and stable β-ZnPc phase (annealed at 300 °C) were 1.3- and 1.5-fold higher, respectively, than that of metastable α-ZnPc standing upright on the ITO substrate. This work provides a fundamental understanding of the crystal phases and orientation changes of the ZnPc molecules, enabling maximization of the light absorption coefficient and the design of efficient small-molecule OPV cells.

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Substrate-driven switchable molecular orientation in bulk heterojunction films identified using infrared reflection absorption spectroscopy

Abstract: Substrate-driven molecular orientation switching could be possible to create electronic devices, such as transistors and solar cells.

Cited by 6 publications

References 35 publications

A simple predictor of interface orientation of fluids of disk-like anisotropic particles and its implications for organic semiconductors

A simple predictor of interface orientation of fluids of disk-like anisotropic particles and its implications for organic semiconductors

A simple predictor of interface orientation of mesogenic fluids and its implications for organic semiconductors

Switchable Crystal Phase and Orientation of Evaporated Zinc Phthalocyanine Films for Efficient Organic Photovoltaics

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