Synthesis and application of H-Bonded cross-linking polymers containing a conjugated pyridyl H-Acceptor side-chain polymer and various carbazole-based H-Donor dyes bearing symmetrical cyanoacrylic acids for organic solar cells

A series of novel hydrogen-bonded (H-bonded) cross-linking polymers were generated by complexing various proton-donor (H-donor) solar cell dyes containing 3,6- and 2,7-functionalized electron-donating carbazole cores bearing symmetrical thiophene linkers and cyanoacrylic acid termini with a proton-acceptor (H-acceptor) side-chain homopolymer carrying pyridyl pendants (with 1/2 M ratio of H-donor/H-acceptor). The supramolecular H-bonded structures between H-donor dyes and the H-acceptor side-chain polymer were confirmed by FTIR measurements. The effects of the supramolecular architecture on optical, electrochemical, and organic photovoltaic (OPV) properties were investigated. From DFT (density functional theory) calculations, the optimized geometries of organic dyes reflected that the carbazole cores of H-donor dyes were coplanar with the conjugated thiophenes and cyanoacrylic acids, which is essential for strong conjugations across the donor-acceptor units in D1-D4 dyes. Under 100 mW/cm² of AM 1.5 white-light illumination, bulk heterojunction (BHJ) OPV cell devices containing an active layer of H-bonded polymers (PDFTP/D1-D4) as an electron donor blended with [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM) as an electron acceptor in a weight ratio of 1:1 were explored. From the preliminary investigations, the OPV device containing 1:1 weight ratio of H-bonded polymer PDFTP/D2 and PCBM showed the best power conversion efficiency (PCE) value of 0.31% with a short-circuit current (J_sc) of 1.9 mA/cm², an open-circuit voltage (V_oc) of 0.55 V, and a fill factor (FF) of 29%, which has a higher PCE value than the corresponding H-donor D2 dye (PCE = 0.15%) or H-acceptor PDFTP homopolymer (PCE = 0.02%) blended with PCBM in 1:1 weight ratio.