HOPV12 - Blogs

4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 168
C51 - Oligomers and alternating copolymers designed for bulk heterojunction solar
cells: synthesis, opto-electronic properties and device performances.
Renaud Demadrille a , Zaireen Yahya a , Evan Spadafora a , Benjamin Grevin a , Mathieu Linares b ,
Patrice Rannou a , Adam Pron a , Remi Debettignies c , Jean-Pierre Travers a
a, CEA-INAC-SPRAM, 17 rue des Martyrs , Grenoble, 38054, FR
b, Department of Computational Physics, IFM, Linkoping University, S-58183, Linkoping, Sweden, SE
c, INES-CEA-RDI-DTS, Laboratoire Cellules Solaires, Le Bourget du Lac, Technolac Chambery, F-73370, France, FR
Nanostructured bulk heterojunctions (BHJ) solar cells, which consist of pi-conjugated
oligomers or polymers as electron donors and fullerenes as electron acceptors, are very
promising in view of their relatively high power conversion efficiency. The inherent advantages
of organic materials such as their light weight and low cost, and the possibility of fabricating
large active area devices facilitated by their solution processability, have stimulated intensive
research in this field during the last decade.
Up to now, BHJ solar cells employing pi-conjugated oligomers or polymers have
demonstrated power conversion efficiencies of ca. 6.7% and 8.3% respectively [1-2]. However,
further improvement in the device performance could be expected, by developping new
materials better matching the solar spectrum and more efficiently converting the sunlight to
electricity.
In the first part of this communication, we will discuss the design rules and the synthesis of
new solution processable oligomers suitable for the use as active components in molecular BHJ
solar cells. Their design is based on the combination of tailor-made oligothiophene segments
as peripheral electron-donor subunits and indacenodithiophenone, benzothiadiazole or
fluorenone as central electron-withdrawing units [3]. The use of this strategy which results in a
significant extension of the absorption spectral range, affords the possibility to finely tune the
energy levels position and the value of their band gap. We will discuss basic supramolecular
chemistry concepts enabling the preparation of molecular nanowires [4-5] and the fabrication
of nanostructured composites using these oligomers.
Figure 1 Chemical structures of fluorenone-based oligomer and polymer studied in this work.
In the second part, we will demonstrate that some of these oligomers can also be
considered as smart building blocks to achieve the synthesis of copolymers showing perfectly
controlled structures, well-suited for solar cells applications.
In the final part, optoelectronic properties of the materials will be described in details and
their electrical performances in devices will be discussed [6]. Promising reliminary results
demonstrate high open circuit voltages (of ca. 0.8-0.9V) and power conversion efficiencies up
to 2.2% for tested devices with an active area of 0.28 cm².
© SEFIN 2012