Supramolecular assembly of h-bonded side-chain polymers containing conjugated pyridyl h-acceptor pendants and various low-band-gap h-donor dyes bearing cyanoacrylic acid groups for organic solar cell applications

Novel supramolecular side-chain polymers were constructed by complexation of proton acceptor (H-acceptor) polymers, i.e., side-chain conjugated polymers P1-P2 containing pyridyl pendants, with low-band-gap proton donor (H-donor) dyes S1-S4 (bearing terminal cyanoacrylic acids) in a proper molar ratio. Besides unique mesomorphic properties confirmed by DSC and XRD results, the H-bonds of supramolecular side-chain structures formed by pyridyl H-acceptors and cyanoacrylic acid H-donors were also confirmed by FTIR measurements. H-donor dyes S1-S4 in solid films exhibited broad absorption peaks located in the range of 471-490 nm with optical band-gaps of 1.99-2.14 eV. Furthermore, H-bonded polymer complexes P1/S1-P1/ S4 and P2/S1-P2/S4 exhibited broad absorption peaks in the range of 440-462 nm with optical band-gaps of 2.11-2.25 eV. Under 100 mW/cm2 of AM 1.5 white-light illumination, the bulk heterojunction polymer solar cell (PSC) devices containing an active layer of H-bonded polymer complexes P1/S1-P1/S4 and P2/S1-P2/S4 (as electron donors) mixed with [6,6]-phenyl C61 butyric acid methyl ester (i.e., PCBM, as an velectron acceptor) in the weight ratio of 1:1 were investigated. The PSC device containing H-bonded polymer complex P1/S3 mixed with PCBM (1:1 w/w) gave the best preliminary result with an overall power conversion efficiency (PCE) of 0.50%, a short-circuit current of 3.17 mA/cm2, an open-circuit voltage of 0.47 V, and a fill factor of 34%.