Journal Article

FZJ-2020-02874

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Relationship between Fill Factor and Light Intensity in Solar Cells Based on Organic Disordered Semiconductors: The Role of Tail States

Xiao, B. ; Calado, P. ; MacKenzie, R. C. I. ; Kirchartz, T.FZJ* ; Yan, J. (Corresponding author) ; Nelson, J.

2020
American Physical Society College Park, Md. [u.a.]

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Please use a persistent id in citations: http://hdl.handle.net/2128/25695  doi:10.1103/PhysRevApplied.14.024034

Abstract: The origin of the relationship between fill factor (FF) and light intensity (I) in organic disordered-semiconductor-based solar cells is studied. An analytical model describing the balance between transport and recombination of charge carriers, parameterized with a factor, Γm, is introduced to understand the FF-I relation, where higher values of Γm correlate to larger FFs. Comparing the effects of direct and tail-state-mediated recombination on the FF-I plot, we find that, for low-mobility systems, direct recombination with constant transport mobility can deliver only a negative dependence of Γm,dir on light intensity. By contrast, tail-state-mediated recombination with trapping and detrapping processes can produce a positive Γm,t versus sun dependency. The analytical model is validated by numerical drift-diffusion simulations. To further validate our model, two material systems that show opposite FF-I behavior are studied: poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-[4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene)-2-carboxylate-2-6-diyl]} (PTB7-Th):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) devices show a negative FF-I relation, while PTB7-Th:(5Z,5′Z)-5,5′-{[7,7′ -(4,4,9,9-tetraoctyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(benzo[c][1,2,5]thiadiazole-7,4-diyl)]bis(methanylylidene)}bis(3-ethyl-2-thioxothiazolidin-4-one) (O-IDTBR) devices show a positive correlation. Optoelectronic measurements show that the O-IDTBR device presents a higher ideality factor, stronger trapping and detrapping behavior, and a higher density of trap states, relative to the PC71BM device, supporting the theoretical model. This work provides a comprehensive understanding of the correlation between FF and light intensity for disordered-semiconductor-based solar cells.

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Contributing Institute(s):

1. Photovoltaik (IEK-5)

Research Program(s):

1. 121 - Solar cells of the next generation (POF3-121) (POF3-121)

Appears in the scientific report 2020

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Database coverage:
; ; ; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; Essential Science Indicators ; IF < 5 ; JCR ; SCOPUS ; Science Citation Index Expanded ; Web of Science Core Collection

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