205 Nanostructured conjugated polymeric systems for photovoltaic applications Corresponding author: V.G.Solovyev, e-mail. solovyev@uni-wuppertal.de Rev.Adv.Mater.Sci. 5 (2003) 205-210 © 2003 Advanced Study Center Co. Ltd. NANOSTRUCTURED CONJUGATED POLYMERIC SYSTEMS FOR PHOTOVOLTAIC APPLICATIONS C.Akbayir, F.Bulut, T.Farrell, A.Goldschmidt, R.Güntner, A.P.Kam, P.Miclea, U.Scherf, J.Seekamp, V.G.Solovyev and C.M.Sotomayor Torres University of Wuppertal, Gauß Straße 20, 42097 Wuppertal, Germany Received: June 11, 2003 Abstract. In this work, conjugated block copolymer polyfluorene/polyaniline (PF/PANI) has been studied as a potential candidate for photovoltaic applications. We used two techniques based on nanoimprint lithography (NIL) for phase alignment of this block copolymer blend PF/PANI, polyaniline being the donor and polyfluorene - the acceptor phase. In the first technique, metallic nanostructures induce nanostructuring in the polymer layer, whereas in the second technique, the PF/PANI is directly patterned with a stamp. The electrical and photoelectrical properties of the polymeric systems were studied and the morphology was characterized by AFM and SEM. 1. INTRODUCTION In the last decade, investigations into the physical properties of organic semiconductors have shown that these materials have several interesting fea- tures as regards applications in photoelectrical de- vices [1]. Of crucial importance to the fabrication of polymeric based solar cells is the requirement of a bicontinuous partition of the donor and acceptor phases to allow effective charge separation and transport to the electrodes. Block copolymers are extremely attractive as candidates for photovoltaic applications as they can phase separate in the 50- 200 nm scale and allow the possibility of fine tun- ing the donor-acceptor energy levels. Conjugated block copolymer polyfluorene/ polyaniline (PF/PANI) is a novel attractive system for photovoltaic applications [2]. It consists of the conjugated homopolymers polyfluorene (PF) and polyaniline (PANI). The conjugated polymer PANI acts as the donor, whereas PF is the acceptor. The light absorption is caused by a π-π* transitions with a maxima at ca. 385 nm for PF and ca. 550 nm for PANI [2]. To obtain a nanostructure formation within the polymeric blend, two experimental techniques based on nanoimprint lithography (NIL) have been used in this work: (i) metallic nanostructures induce a nanostructuring of the polymer layer; and (ii) the PF/PANI is directly patterned by NIL. Two point photoelectrical measurements, atomic force micros- copy (AFM) and scanning electron microscopy (SEM) have been used to visualize the different phases of PF/PANI. 2. EXPERIMENTAL TECHNIQUE 2.1. Synthesis of conjugated rod-rod block copolymers We have developed an improved synthetic route to- wards 4-aminophenyl end-functionalized poly- fluorenes and PF/PANI block copolymers wherein, we have switched from the initially used aryl-aryl cross coupling reaction according to Suzuki to the Yamamoto aryl-aryl coupling procedure. The advan- tage of the Yamamoto route is that it allows the use of unprotected 4-aminophenyl derivatives as endcappers instead of a 4-nitrobenzene derivate, which must be reduced in an additional reaction step. Moreover, the novel method guarantees a complete end-functioanlization of the PF block. The one-step synthesis of 4-aminophenyl end-functionalized