Photo-Cross-Linkable Azide-Functionalized Polythiophene for Thermally Stable Bulk Heterojunction Solar Cells

• Published in: Macromolecules 2012-03, Vol.45 (5), p.2338-2347
• Main Authors: Nam, Chang-Yong, Qin, Yang, Park, Young S, Hlaing, Htay, Lu, Xinhui, Ocko, Benjamin M, Black, Charles T, Grubbs, Robert B
• Format: Article
• Language: English
• Subjects: Applied sciences; Energy; Exact sciences and technology; Natural energy; Organic polymers; Photovoltaic conversion; Physicochemistry of polymers; Polymers with particular properties; Preparation, kinetics, thermodynamics, mechanism and catalysts; Solar cells. Photoelectrochemical cells; Solar energy
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma3001725

We have synthesized photo-cross-linkable azide-functionalized poly(3-hexylthiophene) to explore improvements in the thermal stability of bulk heterojunction solar cells. Exposing blends of photo-cross-linkable polythiophene and [6,6]-phenyl-C61-butyric acid methyl ester to ultraviolet light preferentially cross-linked the polythiophene without degrading its optical or electrical properties. X-ray scattering measurements showed that cross-linking slightly compacted the polythiophene chain lamellar stacking while increasing the polymer crystal coherence length by 20%. Optimized solar cells having cross-linked active blend layers retained 65% of their initial photovoltaic power conversion efficiency after 40 h of thermal annealing at 110 °C, while devices using un-cross-linked commercial polythiophene underwent significant phase separation and retained less than 30% of their initial efficiency after annealing.