New iridium(III) cyclometalates with extended absorption features for bulk heterojunction solar cells

Two new iridium(III) cyclometalates (A and B) based on 2-[5-(9,9′-diethyl-9H-fluoren-7-yl)thienyl]-pyridine were synthesized, characterized and applied in bulk-heterojunction solar cells (BHJSCs). Their absorption, electrochemical, thermal and photovoltaic properties have been investigated. The results reveal that the replacement of phenyl ring by thienyl one can extend the absorption wavelength up to 530 nm, thus narrowing the energy gap (Eg) to 2.93 eV and 2.81 eV for A and B, respectively. These complexes exhibit excellent thermal stability with the onset decomposition temperature at 5% weight-loss (Td) of over 370 °C. The BHJSC device with A as donor blended with [6,6]-phenyl C61-butyric acid methyl ester (PCBM) gave the best power conversion efficiency (η) of 0.51%, with a short-circuit photocurrent density (Jsc) of 2.68 mA cm-2, an open-circuit photovoltage (Voc) of 0.66 V and a fill factor (ff) of 0.28 under illumination of an AM 1.5 solar cell simulator.