Determining the optimum morphology in high-performance polymer-fullerene organic photovoltaic cells

Gordon J. Hedley; Alexander J. Ward; Alexander Alekseev; Calvyn T. Howells; Emiliano R. Martins; Luis A. Serrano; Graeme Cooke; Arvydas Ruseckas; Ifor D.W. Samuel

doi:10.1038/ncomms3867

Determining the optimum morphology in high-performance polymer-fullerene organic photovoltaic cells

Gordon J. Hedley, Alexander J. Ward, Alexander Alekseev, Calvyn T. Howells, Emiliano R. Martins, Luis A. Serrano, Graeme Cooke, Arvydas Ruseckas, Ifor D.W. Samuel

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Abstract

The morphology of bulk heterojunction organic photovoltaic cells controls many of the performance characteristics of devices. However, measuring this morphology is challenging because of the small length-scales and low contrast between organic materials. Here we use nanoscale photocurrent mapping, ultrafast fluorescence and exciton diffusion to observe the detailed morphology of a high-performance blend of PTB7:PC 71 BM. We show that optimized blends consist of elongated fullerene-rich and polymer-rich fibre-like domains, which are 10-50 nm wide and 200-400 nm long. These elongated domains provide a concentration gradient for directional charge diffusion that helps in the extraction of charge pairs with 80% efficiency. In contrast, blends with agglomerated fullerene domains show a much lower efficiency of charge extraction of ∼45%, which is attributed to poor electron and hole transport. Our results show that the formation of narrow and elongated domains is desirable for efficient bulk heterojunction solar cells.

Original language	British English
Article number	2867
Journal	Nature Communications
Volume	4
DOIs	https://doi.org/10.1038/ncomms3867
State	Published - 17 Dec 2013

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@article{7839bfa0a53f4804962a32675afeee54,

title = "Determining the optimum morphology in high-performance polymer-fullerene organic photovoltaic cells",

abstract = "The morphology of bulk heterojunction organic photovoltaic cells controls many of the performance characteristics of devices. However, measuring this morphology is challenging because of the small length-scales and low contrast between organic materials. Here we use nanoscale photocurrent mapping, ultrafast fluorescence and exciton diffusion to observe the detailed morphology of a high-performance blend of PTB7:PC 71 BM. We show that optimized blends consist of elongated fullerene-rich and polymer-rich fibre-like domains, which are 10-50 nm wide and 200-400 nm long. These elongated domains provide a concentration gradient for directional charge diffusion that helps in the extraction of charge pairs with 80% efficiency. In contrast, blends with agglomerated fullerene domains show a much lower efficiency of charge extraction of ∼45%, which is attributed to poor electron and hole transport. Our results show that the formation of narrow and elongated domains is desirable for efficient bulk heterojunction solar cells.",

author = "Hedley, {Gordon J.} and Ward, {Alexander J.} and Alexander Alekseev and Howells, {Calvyn T.} and Martins, {Emiliano R.} and Serrano, {Luis A.} and Graeme Cooke and Arvydas Ruseckas and Samuel, {Ifor D.W.}",

note = "Funding Information: This work was supported by the Engineering and Physical Sciences Research Council (grant number EP/I013288/1) and from the European Union Seventh Framework Programme under grant agreement 321305. Travel to Russia was supported by The Ministry of Education and Science of Russian Federation, project 14.A18.21.0887. Underlying research materials can be accessed by contacting the corresponding author. We are grateful to Sylvia Williamson for assistance and advice with the DSC measurements.",

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doi = "10.1038/ncomms3867",

language = "British English",

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journal = "Nature Communications",

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AU - Hedley, Gordon J.

AU - Ward, Alexander J.

AU - Alekseev, Alexander

AU - Howells, Calvyn T.

AU - Martins, Emiliano R.

AU - Serrano, Luis A.

AU - Cooke, Graeme

AU - Ruseckas, Arvydas

AU - Samuel, Ifor D.W.

N1 - Funding Information: This work was supported by the Engineering and Physical Sciences Research Council (grant number EP/I013288/1) and from the European Union Seventh Framework Programme under grant agreement 321305. Travel to Russia was supported by The Ministry of Education and Science of Russian Federation, project 14.A18.21.0887. Underlying research materials can be accessed by contacting the corresponding author. We are grateful to Sylvia Williamson for assistance and advice with the DSC measurements.

PY - 2013/12/17

Y1 - 2013/12/17

N2 - The morphology of bulk heterojunction organic photovoltaic cells controls many of the performance characteristics of devices. However, measuring this morphology is challenging because of the small length-scales and low contrast between organic materials. Here we use nanoscale photocurrent mapping, ultrafast fluorescence and exciton diffusion to observe the detailed morphology of a high-performance blend of PTB7:PC 71 BM. We show that optimized blends consist of elongated fullerene-rich and polymer-rich fibre-like domains, which are 10-50 nm wide and 200-400 nm long. These elongated domains provide a concentration gradient for directional charge diffusion that helps in the extraction of charge pairs with 80% efficiency. In contrast, blends with agglomerated fullerene domains show a much lower efficiency of charge extraction of ∼45%, which is attributed to poor electron and hole transport. Our results show that the formation of narrow and elongated domains is desirable for efficient bulk heterojunction solar cells.

AB - The morphology of bulk heterojunction organic photovoltaic cells controls many of the performance characteristics of devices. However, measuring this morphology is challenging because of the small length-scales and low contrast between organic materials. Here we use nanoscale photocurrent mapping, ultrafast fluorescence and exciton diffusion to observe the detailed morphology of a high-performance blend of PTB7:PC 71 BM. We show that optimized blends consist of elongated fullerene-rich and polymer-rich fibre-like domains, which are 10-50 nm wide and 200-400 nm long. These elongated domains provide a concentration gradient for directional charge diffusion that helps in the extraction of charge pairs with 80% efficiency. In contrast, blends with agglomerated fullerene domains show a much lower efficiency of charge extraction of ∼45%, which is attributed to poor electron and hole transport. Our results show that the formation of narrow and elongated domains is desirable for efficient bulk heterojunction solar cells.

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Determining the optimum morphology in high-performance polymer-fullerene organic photovoltaic cells

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