@article{Xiao:2020:10.1103/PhysRevApplied.14.024034,
author = {Xiao, B and Calado, P and Mackenzie, R and Kirchartz, T and Yan, J and Nelson, J},
doi = {10.1103/PhysRevApplied.14.024034},
journal = {Physical Review Applied},
pages = {024034  1--024034  17},
title = {Relationship between fill factor and light intensity in solar cells based on organic disordered semiconductors: The role of tail states},
url = {http://dx.doi.org/10.1103/PhysRevApplied.14.024034},
volume = {14},
year = {2020}
}

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TY  - JOUR
AB  - 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.
AU  - Xiao,B
AU  - Calado,P
AU  - Mackenzie,R
AU  - Kirchartz,T
AU  - Yan,J
AU  - Nelson,J
DO  - 10.1103/PhysRevApplied.14.024034
EP  - 1
PY  - 2020///
SN  - 2331-7019
SP  - 024034
TI  - Relationship between fill factor and light intensity in solar cells based on organic disordered semiconductors: The role of tail states
T2  - Physical Review Applied
UR  - http://dx.doi.org/10.1103/PhysRevApplied.14.024034
UR  - https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.14.024034
UR  - http://hdl.handle.net/10044/1/81296
VL  - 14
ER  - 

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