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Key molecular perspectives for high stability in organic photovoltaics

Nature Reviews Materials volume 8, pages 839–852 (2023)Cite this article

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Abstract

Organic photovoltaics (OPVs) have rapidly improved in efficiency, with single-junction cells now exceeding 18% efficiency. These improvements have been driven by the adoption of new non-fullerene acceptors and the fine tuning of their molecular structures. Although OPVs are highly efficient, they often show extremely poor operational stability, primarily owing to the complex interplay between the morphological instability of the blended bulk heterojunction photoactive layers and the intrinsically poor photostability of the organic semiconductor materials themselves. To realize commercialization, it is vital to understand the degradation mechanisms of these organic materials to improve their stability. Efficiency increases have, in part, been driven by the rational molecular design of materials. In this Perspective, we examine how a similar bottom-up molecular design can be applied to OPV stability. Specifically, we highlight key molecular design parameters and demonstrate how each parameter impacts different degradation pathways. Looking forward, we propose that fundamental understanding of the molecular origin of OPV stability is a key research theme for next-generation OPVs. Additionally, we discuss the tools required, across length scales, to implement these design rules, particularly the use of in situ Raman spectroscopy as a critical bridge linking the molecular scale to the nanoscale and beyond.

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Fig. 1: Key advances in organic photovoltaic development.
Fig. 2: Controllable molecular parameters.
Fig. 3: Molecular structure impact on stability.
Fig. 4: Key molecular design rules for non-fullerene acceptors to improve stability.
Fig. 5: Raman spectroscopy as a probe for molecular-level understanding of stability.

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Acknowledgements

The authors would like to acknowledge the UK Engineering and Physical Sciences Research Council for funding through both the Application Targeted and Integrated Photovoltaics programme grant (EP/T028513/1) and the Centre for Doctoral Training in Plastic Electronic Materials (EP/L016702/1). Thanks also go to Samsung Electronics for funding. Special thanks also go to M. Heeney (Imperial College London, KAUST Solar Center) for his helpful thoughts and comments.

Author information

Authors and Affiliations

  1. Department of Physics, Imperial College London, London, UK

    Joel Luke, Emily J. Yang, Chiara Labanti, Song Yi Park & Ji-Seon Kim

  2. Centre for Processable Electronics, Imperial College London, London, UK

    Joel Luke, Emily J. Yang, Chiara Labanti, Song Yi Park & Ji-Seon Kim

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  1. Joel Luke
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  2. Emily J. Yang
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  4. Song Yi Park
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Contributions

All authors researched data for the article and contributed substantially to discussion of the content. J.L. wrote the article with assistance from E.Y., C.L. and S.Y.P. J.-S.K. and J.L. reviewed and/or edited the manuscript before submission.

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Correspondence to Joel Luke or Ji-Seon Kim.

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Glossary

D18

poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-5,5′-(5,8-bis(4-(2-butyloctyl)thiophen-2-yl)dithieno[3′,2′:3,4;2″,3″:5,6]benzo[1,2-c][1,2,5]thiadiazole)].

IDTBR

(5Z)-3-ethyl-2-sulfanylidene-5-[[4-[9,9,18,18-tetrakis(R)-15-[7-[(Z)-(3-ethyl-4-oxo-2-sulfanylidene-1,3-thiazolidin-5-ylidene)methyl]-2,1,3-benzothiadiazol-4-yl]-5,14-dithiapentacyclo[10.6.0.03,10.04,8.013,17]octadeca-1(12),2,4(8),6,10,13(17),15-heptaen-6-yl]-2,1,3-benzothiadiazol-7-yl]methylidene]-1,3-thiazolidin-4-one where R is either n-octyl in O-IDTBR or 2-ethylhexyl in EH-IDTBR.

IT-4F

2-[(2Z)-2-[[20-[(Z)-[1-(dicyanomethylidene)-5,6-difluoro-3-oxoinden-2-ylidene]methyl]-12,12,24,24-tetrakis(4-hexylphenyl)-5,9,17,21-tetrathiaheptacyclo[13.9.0.03,13.04,11.06,10.016,23.018,22]tetracosa-1(15),2,4(11),6(10),7,13,16(23),18(22),19-nonaen-8-yl]methylidene]-5,6-difluoro-3-oxoinden-1-ylidene]propanedinitrile.

ITIC

2-[2-[[20-[(Z)-[1-(dicyanomethylidene)-3-oxoinden-2-ylidene]methyl]-12,12,24,24-tetrakis(4-hexylphenyl)-5,9,17,21-tetrathiaheptacyclo[13.9.0.03,13.04,11.06,10.016,23.018,22]tetracosa-1(15),2,4(11),6(10),7,13,16(23),18(22),19-nonaen-8-yl]methylidene]-3-oxoinden-1-ylidene]propanedinitrile.

ITIC-DM

2-[(2Z)-2-[[20-[(E)-[1-(dicyanomethylidene)-5,6-dimethyl-3-oxoinden-2-ylidene]methyl]-12,12,24,24-tetrakis(4-hexylphenyl)-5,9,17,21-tetrathiaheptacyclo[13.9.0.03,13.04,11.06,10.016,23.018,22]tetracosa-1(15),2,4(11),6(10),7,13,16(23),18(22),19-nonaen-8-yl]methylidene]-5,6-dimethyl-3-oxoinden-1-ylidene]propanedinitrile.

L8-BO

2-[2-[[23-[[1-(dicyanomethylidene)-5,6-difluoro-3-oxoinden-2-ylidene]methyl]-3,27-bis(2-ethylhexyl)-8,22-di(2-butyloctyl)-6,10,15,20,24-pentathia-3,14,16,27-tetrazaoctacyclo[16.9.0.02,12.04,11.05,9.013,17.019,26.021,25]heptacosa-1(18),2(12),4(11),5(9),7,13,16,19(26),21(25),22-decaen-7-yl]methylidene]-5,6-difluoro-3-oxoinden-1-ylidene]propanedinitrile.

O-IDFBR

(5Z)-3-ethyl-5-[[4-[2-[7-[(Z)-(3-ethyl-4-oxo-2-sulfanylidene-1,3-thiazolidin-5-ylidene)methyl]-2,1,3-benzothiadiazol-4-yl]-6,6,12,12-tetraoctylindeno[1,2-b]fluoren-8-yl]-2,1,3-benzothiadiazol-7-yl]methylidene]-2-sulfanylidene-1,3-thiazolidin-4-one.

P3HT

poly(3-hexylthiophene-2,5-diyl).

PBDB-T

poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione)].

PM6

poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione)].

PTIC

2-((Z)-2-((5-(4-(5-(((1E,2Z)-1-(cyano(isocyano)methylene)-5,6-difluoro-3-oxo-1,3-dihydro-2H-inden-2-ylidene)methyl)-4-hexylthiophen-2-yl)-2-((2-hexyldecyl)oxy)-5-(pentadecan-7-yloxy)phenyl)-3-hexylthiophen-2-yl)methylene)-5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile.

Y6

2-[2-[[23-[[1-(dicyanomethylidene)-5,6-difluoro-3-oxoinden-2-ylidene]methyl]-3,27-bis(2-ethylhexyl)-8,22-di(undecyl)-6,10,15,20,24-pentathia-3,14,16,27-tetrazaoctacyclo[16.9.0.02,12.04,11.05,9.013,17.019,26.021,25]heptacosa-1(18),2(12),4(11),5(9),7,13,16,19(26),21(25),22-decaen-7-yl]methylidene]-5,6-difluoro-3-oxoinden-1-ylidene]propanedinitrile.

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Luke, J., Yang, E.J., Labanti, C. et al. Key molecular perspectives for high stability in organic photovoltaics. Nat Rev Mater 8, 839–852 (2023). https://doi.org/10.1038/s41578-023-00606-5

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