Correlation of Nano-morphology with Structural and Spectroscopic Studies in Organic Solar Cells

Published

October 27, 2020

Author(s)

Eliot Gann, Christopher McNeill, Wenchao Huang, Dinesh Kabra, Urvashi Bothra, Nakul Jain, Amelia C. Liu

Abstract

The nano-morphology of bulk heterojunction blends based on poly[[4,8-bis[(2- ethylhexyl)oxy]benzo[1,2-b:4,5- b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) blended with [6,6]- phenyl-C71-butyric acid methyl ester (PC71BM) is systematically varied by varying the volume fraction of the solvent additive 1,8-diiodooctane (DIO) from 0 vol% to 20 vol% in the casting solution. With increasing addition of DIO, the photoluminescence (PL) from the blend is reduced, however, a relative increase in PL from 750 nm onwards is observed for blends with 20 vol% DIO. As quenching of the blend PL is related to the donor/acceptor (D/A) interface, structural characterizations are performed to unravel the morphology of blend systems to correlate nano- morphology with photophysical and charge transport processes. Blends prepared with 0 vol% DIO form large phase separated domains of PCBM, hundreds of nanometers in diameter. With the addition of 3 vol% DIO the size of PCBM domains is supressed resulting in a more mixed morphology due to the selective dissolution of DIO in PC71BM. On the addition of up to 20 vol% of DIO, the film becomes rougher with a finer interconnected morphology due to polymer aggregation, which contrasts with previous reports. Electron transport lengths measured by scanning photocurrent microscopy are found to increase with the addition of up to 3 vol% DIO associated with the break-up of the large PC71BM aggregates, while the hole transport length is found to increase on adding DIO up to 20 vol% due to aggregation of polymer chains. The structural results are found to be in good agreement with the PL quenching and the transport lengths. This work represent a unique set of results systematically examining the effect of nano- morphology on structural and opto-electronic properties of PTB7:PCBM blends on the addition of solvent additive DIO, which has implications beyond the system studied.

Citation

ACS Applied Nano Materials

Pub Type

Journals

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Keywords

organic solar cells, solvent additive, morphology, domain size, spectroscopy

Citation

Gann, E. , McNeill, C. , Huang, W. , Kabra, D. , Bothra, U. , Jain, N. and Liu, A. (2020), Correlation of Nano-morphology with Structural and Spectroscopic Studies in Organic Solar Cells, ACS Applied Nano Materials, [online], https://doi.org/10.1021/acsanm.0c02256 (Accessed April 18, 2024)