Quantitative comparison of organic photovoltaic bulk heterojunction photostability under laser illumination

Journal Article · Thu Nov 20 00:00:00 EST 2014 · Journal of Physical Chemistry. C

DOI:https://doi.org/10.1021/jp509589g· OSTI ID:1234517

Lesoine, Michael D. ^[1]; Bobbitt, Jonathan M. ^[1]; Carr, John A. ^[2]; Elshobaki, Moneim ^[3]; Chaudhary, Sumit ^[2]; Smith, Emily A. ^[1]

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1. Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)
2. Iowa State Univ., Ames, IA (United States)
3. Iowa State Univ., Ames, IA (United States); Mansoura Univ., Mansoura (Egypt)

The photostability of bulk heterojunction organic photovoltaic films containing a polymer donor and a fullerene-derivative acceptor was examined using resonance Raman spectroscopy and controlled laser power densities. The polymer donors were poly(3-hexylthiophene-2,5-diyl) (P3HT), poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] (PCDTBT), or 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). Four sample preparation methods were studied: (i) thin or (ii) thick films with fast solvent evaporation under nitrogen, (iii) thick films with slow solvent evaporation under nitrogen, and (iv) thin films dried under nitrogen followed by thermal annealing. Polymer order was assessed by monitoring a Raman peak’s full width at half-maximum and location as a function of illumination time and laser power densities from 2.5 × 10³ to 2.5 × 10⁵ W cm^–2. Resonance Raman spectroscopy measurements show that before prolonged illumination, PCDTBT and PTB7 have the same initial order for all preparation conditions, while P3HT order improves with slow solvent drying or thermal annealing. All films exhibited changes to bulk heterojunction structure with 2.5 × 10⁵ Wcm^–2 laser illumination as measured by resonance Raman spectroscopy, and atomic force microscopy images show evidence of sample heating that affects the polymer over an area greater than the illumination profile. Furthermore, photostability data are important for proper characterization by techniques involving illumination and the development of devices suitable for real-world applications.

• Research Organization: Ames Lab., Ames, IA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: ECCS1055930; AC02-07CH11358; GM915
• OSTI ID: 1234517
• Report Number(s): IS-J-8422
• Journal Information: Journal of Physical Chemistry. C, Vol. 118, Issue 51; ISSN 1932-7447
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
resonance raman spectroscopy
thin films
P3HT
PCDTBT
PTB7