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Abstract: New random poly{benzo[1,2-b:4,5-b'']dithiophene-thieno[3,4-c]pyrrole-4,6-dione-pyrrolo[3,4-c]pyrrole-1,4-dione} (PBDT-TPD-DPP) based on benzo[1,2-b:4,5-b'']dithiophene (BDT) as donor and thieno[3,4-c]pyrrole-4,6-dione (TPD, 60–90%), pyrrolo[3,4-c]pyrrole-1,4-dione (DPP, 10–40%) as acceptors were synthesized through Stille coupling reaction. The photophysical, electrochemical and photovoltaic properties of random polymers were investigated. The random polymers with high molecular weight (M n = 33.5–41.7 kDa) exhibited broad and strong absorption covering the spectra range from 350 nm up to 922 nm with absorption maxima at around 700 nm, the relatively deep highest occupied molecular orbital (HOMO) energy levels vary between −5.25 and −5.42 eV and suitable lowest unoccupied molecular orbital (LUMO) energy levels ranging from −3.85 to −3.91 eV. Polymer solar cells (PSC) based on these new random polymers were fabricated with device structures of ITO/PEDOT: PSS/random polymers: PC71BM (1:2, w/w)/Ca/Al. The photovoltaic properties of random polymers were evaluated under AM 1.5G illumination (100 mW/cm2). Devices based on the random polymers showed open circuit voltage (V oc) of 0.71–0.83 V, and power conversion efficiency (PCE) of 0.82–1.80%. [Copyright &y& Elsevier]

Abstract: Red light-emitting electrophosphorescent polymers with poly(fluorene-alt-carbazole) (PFCz) and poly(3,6-carbazole) (PCz) as the main chain, and the quinoline-based iridium (Ir) complex as the side chain have been synthesized by Suzuki and modified Yamamoto polymerization, respectively. The triplet energy of the polymeric backbone is tuned from 2.1 eV of polyfluorene (PF) to 2.3 eV of PFCz and 2.6 eV of PCz. We find that, with the increasing triplet energy, the lifetime of the triplet excitons gradually increases, but the device efficiency becomes worse. The reason is that the alteration of the main chain structure leads to the increase of the highest occupied molecular orbital (HOMO) level of the polymeric host, which can facilitate the efficient hole injection and transportation. As a consequence of this enhancement of the hole current, charge balance in the emitting layer is destroyed, and correspondingly, the poorer device performance is achieved. Our results, we believe, indicate that besides the triplet energy, charge balance is a crucial determinant to develop high efficiency red light-emitting electrophosphorescent polymers. [Copyright &y& Elsevier]