Special Section on Organic Photovoltaics

Connecting physical properties of spin-casting solvents with morphology, nanoscale charge transport, and device performance of poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester bulk heterojunction solar cells

[+] Author Affiliations
Pavel Dutta, Yu Xie, Mukesh Kumar, David Galipeau, Qiquan Qiao, Venkat Bommisetty

South Dakota State University, Department of Electrical Engineering, Brookings, South Dakota 57007 venkat.bommisetty@sdstate.edu

Monika Rathi, Phil Ahrenkiel

South Dakota School of Mines and Technology, Nanoscience and Nanoengineering Department, Rapid City, South Dakota 57701

J. Photon. Energy. 1(1), 011124 (November 18, 2011). doi:10.1117/1.3662467
History: Received July 25, 2011; Revised October 06, 2011; Accepted October 28, 2011; Published November 18, 2011; Online November 18, 2011
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The correlation between the physical properties of spin-casting solvents, film morphology, nanoscale charge transport, and device performance was studied in poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) blends, spin cast with two halogenated aromatic solvents: chlorobenzene (CB) and ortho-dichlorobenzene (1,2-DCB). 1,2-DCB–based blends exhibited fine phase separation of ∼10 to 15 nm length scale with ordered self-assembly of P3HT whereas blends spin cast from CB showed coarse phase separation with large isolated clusters of ∼25 to 100 nm of donor- and acceptor-rich regions. Higher solubility of both P3HT and PCBM in 1,2-DCB and a slower drying rate of 1,2-DCB (because of higher boiling point) facilitated self-organization and ordering of P3HT and promoted finer phase separation. Higher local hole mobility in 1,2-DCB–based blend was attributed to efficient hole transport through the ordered network of P3HT chains. Moreover, higher local illuminated current (dark + photocurrent) in 1,2-DCB–based blend suggested efficient diffusion and dissociation of excitons due to finer phase separation. As a consequence, 1,2-DCB–based devices exhibited higher short circuit current density (Jsc), external quantum efficiency and power conversion efficiency in contrast to the CB-based device. It was also observed that the device performance was not limited by light absorption and exciton generation; rather morphology dependent processes subsequent to exciton generation, primarily charge transport to the electrodes, limited device performance.

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© 2011 Society of Photo-Optical Instrumentation Engineers (SPIE)

Citation

Pavel Dutta ; Yu Xie ; Mukesh Kumar ; Monika Rathi ; Phil Ahrenkiel, et al.
"Connecting physical properties of spin-casting solvents with morphology, nanoscale charge transport, and device performance of poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester bulk heterojunction solar cells", J. Photon. Energy. 1(1), 011124 (November 18, 2011). ; http://dx.doi.org/10.1117/1.3662467


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