Solution processable benzotriazole and fluorene containing copolymers for photovoltaic applications

2-Dodecyl benzotriazole and 9,9-dioctylfluorene containing alternating copolymers poly((9,9-dioctylfluorene)-2,7-diyl-(2-dodecyl-benzo[1,2,3]triazole)) (P1), poly((9,9-dioctylfluorene)-2,7-diyl-(4,7-bis(thien-2-yl) 2-dodecyl-benzo[1,2,3]triazole)) (P2), poly((9,9-dioctylfluorene)-2,7-diyl-(4,7-bis(3-hexylthien-5-yl) 2-dodecyl benzo[1,2,3]triazole)) (P3) were synthesized via a typical Suzuki coupling polymerization. UV–vis and electrochemical studies indicated that polymers have desirable HOMO–LUMO and band gap energy levels, enabling efficient electron transfer when blending them with fullerene derivatives. Photovoltaic properties of the copolymers mixed with [6,6] phenyl-C61-butyric acid methyl ester (PCBM), were investigated. P2 exhibited the best device performance with an open circuit voltage of 0.6 V, short circuit current of 3.4 mA/cm2 and power conversion efficiency of 0.56% under Air mass 1.5 Global (AM 1.5G, 100 mW/cm2) illumination. Hole mobilities of the polymers were calculated using space charge limited current (SCLC) method and found to be in the order of 10−5 for P1 and P2 and 10−4 for P3.

► New donor polymers P1–P2 and P3 are synthesized via Suzuki cross coupling of a fluorene diboronic ester.
► UV–vis and electrochemistry studies confirmed suitability of polymers for solar cell applications.
► Polymers' photovoltaic outcomes are investigated.
► Highest efficiency was achieved with P2 as 0.56%.