ABSTRACT
530It is the objective of this chapter to show the correlation between optoelectronic properties of different donor polymer-fullerene acceptor combinations (acceptors: C60, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), and bismorpholino-C60) as well as their influence on the parameters of corresponding photovoltaic devices. Therefore the following optoelectronic properties have been considered: absorption coefficients, detection of photoinduced donor-acceptor charge transfer (CT) (by photoluminescence (PL) quenching experiments and light-induced electron spin resonance spectroscopy), and the determination of highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels of donors and acceptors by means of cyclic voltammetry. Regio-regular poly(3-alkylthiophene)s (P3AT) (poly(3-hexylthiophene), poly(3-ocylthio-phene), poly(3-dodecylthiophene)) were investigated concerning the influence of the alkyl side chain length on the optoelectronic properties and on the photovoltaic device parameters in P3AT/PCBM (1:3 wt.%) composites. Novel phenylene ethynylene/phenylene vinylene (PPE-PPV) hybrid polymers DE69 and DE21 were compared with the state-of-the-art material poly[2-methoxy-5-(3′,7′-dimethyl-octyloxy)-1,4-phenylene vinylene] (MDMO-PPV). The presence of — C≡C— within the polymer backbone leads to a higher oxidation potential (helpful to improve the intrinsic material stability), energetically lower HOMO-LUMO levels and higher optical bandgaps for the hybrid polymers. Photovoltaic devices were prepared on ambient conditions on flexible PET-ITO foils with MDMO-PPV/PCBM, giving ηAM1.5 = 3% and the new polymers DE69 or DE21/ PCBM with ηAM1.5 = 1.75% and 0.5% (A = 0.25 cm2, P IN = 100mW/cm2).
