Probing the annealing induced molecular ordering in bulk heterojunction polymer solar cells using in-situ Raman spectroscopy

• Published in: Solar energy materials and solar cells Vol. 120; pp. 526 - 535
• Main Authors: Veerender, P., Saxena, Vibha, Chauhan, A.K., Koiry, S.P., Jha, P., Gusain, Abhay, Choudhury, Sipra, Aswal, D.K., Gupta, S.K.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-01-2014; Elsevier
• Subjects: Annealing; Applied sciences; Cooling; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Energy; Evolution; Exact sciences and technology; Heating; in-situ Raman spectroscopy; Natural energy; Optical microscopy; Order disorder; P3HT:PCBM; Photoelectric conversion; Photovoltaic cells; Photovoltaic conversion; Polymer solar cell; Solar cells; Solar cells. Photoelectrochemical cells; Solar energy; Thermal annealing; in-situ Raman spectroscopy; P3HT:PCBM; Thermal annealing; Polymer solar cell; Atomic force microscopy; Heat treatment; Disordered system; Fullerene compounds; In situ; Temperature effect; Mapping; Organic solar cells; Butyric acid; Ester; Optical microscopy; Thiophene derivative polymer; Ordering; Raman spectrometry; Stretching; Heterojunction; Temperature dependence; Scanning electron microscopy; Cooling; Solar cell; Heating; Morphology; Ultraviolet visible spectrometry
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2013.09.034

We have carried out temperature dependent in-situ Raman as well as optical microscopy of poly(3-hexylthiophene) and [6,6]-phenyl-C71 butyric acid methyl ester (P3HT:PCBM) films to investigate the structural and morphological evolution during heating and cooling cycles of thermal annealing. The full-width half-maximum of symmetric CåC stretching mode, CåC/C–C intensity ratio and Raman shift of CåC mode of P3HT measured during heating upto 130°C as well as subsequent cooling revealed that: (i) molecular disorder in P3HT chains increase during heating cycle and (ii) on cooling the molecular ordering enhances rapidly at ~100°C. However, heating to higher temperatures (>150°C) leads to the formation of PCBM aggregates. The mechanism of morphology evolution in P3HT:PCBM films envisaged through in-situ Raman and optical microscopy has been confirmed by other ex-situ techniques, such as, atomic force microscopy, scanning electron microscopy, UV–vis spectroscopy and X-ray elemental mapping. A correlation between the morphological evolution and various photovoltaic parameters of the fabricated P3HT:PCBM solar cells has been established.
[Display omitted]
•In-situ Raman as well as optical microscopy of poly(3-hexylthiophene) and [6,6]-phenyl-C71 butyric acid methyl ester films to investigate structural and morphological evolution.•Molecular disorder in P3HT chains increases during heating cycle and enhances rapidly at ~100°C during cooling.•A correlation between morphological evolution and photovoltaic parameters of fabricated P3HT:PCBM solar cells has been established.