TY  - JOUR
AU  - Xiao, Biao
AU  - Calado, Philip
AU  - MacKenzie, Roderick C. I.
AU  - Kirchartz, Thomas
AU  - Yan, Jun
AU  - Nelson, Jenny
TI  - Relationship between Fill Factor and Light Intensity in Solar Cells Based on Organic Disordered Semiconductors: The Role of Tail States
JO  - Physical review applied
VL  - 14
IS  - 2
SN  - 2331-7019
CY  - College Park, Md. [u.a.]
PB  - American Physical Society
M1  - FZJ-2020-02874
SP  - 024034
PY  - 2020
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.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000560631000003
DO  - DOI:10.1103/PhysRevApplied.14.024034
UR  - https://juser.fz-juelich.de/record/878470
ER  -