Influence of the Electron Deficient Co‐Monomer on the Optoelectronic Properties and Photovoltaic Performance of Dithienogermole‐based Co‐Polymers. (27th October 2013)

• Record Type: Journal Article
• Authors: Yau, Chin Pang; Fei, Zhuping; Ashraf, Raja Shahid; Shahid, Munazza; Watkins, Scott E.; Pattanasattayavong, Pichaya; Anthopoulos, Thomas D.; Gregoriou, Vasilis G.; Chochos, Christos L.; Heeney, Martin
• Is Part Of: Advanced functional materials. Volume 24:Number 5(2014)
• Page Start: 678
• Page End: 687
• Publication Date: 2013-10-27
• Subjects: Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adfm.201302270
• Languages: English
• ISSNs: 1616-301X

Abstract

<abstract abstract-type="main" xml:lang="en"> <title> <x xml:space="preserve">Abstract</x> </title> <p>A series of donor–acceptor (D–A) conjugated polymers utilizing 4, 4‐bis(2‐ethylhexyl)‐4<italic>H</italic>‐germolo[3, 2‐<italic>b</italic>:4, 5‐<italic>b</italic>′]dithiophene (<bold>DTG</bold>) as the electron rich unit and three electron withdrawing units of varying strength, namely 2‐octyl‐2<italic>H</italic>‐benzo[<italic>d</italic>][1, 2, 3]triazole (<bold>BTz</bold>), 5, 6‐difluorobenzo[<italic>c</italic>][1, 2, 5]thiadiazole (<bold>DFBT</bold>) and [1, 2, 5]thiadiazolo[3, 4‐<italic>c</italic>]pyridine (<bold>PT</bold>) are reported. It is demonstrated how the choice of the acceptor unit (<bold>BTz</bold>, <bold>DFBT</bold>, <bold>PT</bold>) influences the relative positions of the energy levels, the intramolecular transition energy (ICT), the optical band gap (<italic>E</italic><sub>g</sub><sup>opt</sup>), and the structural conformation of the <bold>DTG</bold>‐based co‐polymers. Moreover, the photovoltaic performance of poly[(4, 4‐bis(2‐ethylhexyl)‐4<italic>H</italic>‐germolo[3, 2‐<italic>b</italic>:4, 5‐<italic>b</italic>′]dithiophen‐2‐yl)‐([1, 2, 5]thiadiazolo[3, 4‐<italic>c</italic>]pyridine)] (<bold>PDTG‐PT</bold>), poly[(4, 4‐bis(2‐ethylhexyl)‐4<italic>H</italic>‐germolo[3, 2‐<italic>b</italic>:4, 5‐<italic>b</italic>′]dithiophen‐2‐yl)‐(2‐octyl‐2<italic>H</italic>‐benzo[<italic>d</italic>][1, 2, 3]triazole)] (<bold>PDTG‐BTz</bold>), and poly[(4, 4‐bis(2‐ethylhexyl)‐4<italic>H</italic>‐germolo[3, 2‐<italic>b</italic>:4, 5‐<italic>b</italic>′]dithiophen‐2‐yl)‐(5, 6‐difluorobenzo[<italic>c</italic>][1, 2, 5]thiadiazole)] (<bold>PDTG‐DFBT</bold>) is studied in blends with [6, 6]‐phenyl‐C<sub>70</sub>‐butyric acid methyl ester (<bold>PC<sub>70</sub>BM</bold>). The highest power conversion efficiency (PCE) is obtained by <bold>PDTG‐PT</bold> (5.2%) in normal architecture. The PCE of <bold>PDTG‐PT</bold> is further improved to 6.6% when the device architecture is modified from normal to inverted. Therefore, <bold>PDTG‐PT</bold> is an ideal candidate for application in tandem solar cells configuration due to its high efficiency at very low band gaps (<italic>E</italic><sub>g</sub><sup>opt</sup> = 1.32 eV). Finally, the 6.6% PCE is the highest reported for all the co‐polymers containing bridged bithiophenes with 5‐member fused rings in the central core and possessing an <italic>E</italic><sub>g</sub><sup>opt</sup> below 1.4 eV.</p> </abstract>