Influence of poly(3-alkylthiophene) (P3ATs) structure on P3AT/Gaq3 films for organic solar cells

Abstract

In this research work, poly(3-hexylthiophene), poly(3-octylthiophene) and poly(3-decylthiophene) with three different alkyl side chain lengths of poly(3-alkylthiophene)-2,5-diyl (P3AT) have been used as electron donor polymeric materials. These polymer materials were mixed with a low molecular weight material of tris-(8-hydroxyquinoline)-gallium (Gaq3) to form the blends of poly(3-hexylthiophene)/Gaq3, poly(3-octylthiophene)/Gaq3 and poly(3-decylthiophene)/Gaq3. The mixtures were spin coated onto solid substrates to produce photoactive layer films. The influence of the alkyl side chain length of P3AT on the optical, morphology and surface properties of P3AT/Gaq3 active layers has been investigated. The light absorption intensity decreases with the increase in the side chain length of the polymer due to the distortion of polymer packing in the film. Rougher surface morphologies were observed for films containing a longer side chain. Additionally, the device with the shortest polymer side chain produces the best photovoltaic properties with a fill factor of 0·36.