Effect of main ligands on organic photovoltaic performance of Ir(III) complexes

The photovoltaic performance of devices fabricated using three iridium complexes (1, 2, and 3) containing different main ligands (1-phenylisoquinoline, (4-isoquinolin-1-yl-phenyl) diphenylamine, and 1-pyren-1-yl-isoquinoline for 1, 2, and 3, respectively) was investigated. Two different devices, one fabricated by spin coating and one produced by vacuum deposition, were tested. Among the bulk heterojunction solar cells (BHJCs) fabricated by spin coating, the cell fabricated using 2 had the highest power conversion efficiency (PCE, 0.50%). The PCEs of 1 and 3 were 0.43% and 0.34%, respectively. These results suggested that the superior hole-transport ability of the triphenylamine moiety in 2 was responsible for the high photovoltaic performance of the device fabricated using this complex. This assumption was confirmed by fabricating electron-only devices using the three Ir complexes and comparing the turn-on voltage of each device. The photovoltaic performance of device C fabricated by the vacuum co-deposition of 2 and C-60 in a 50 nm-thick active layer was 50% higher than that of device A (bilayer heterojunction solar cell) and device B (fabricated by the co-deposition of 2 and C-60 with a 30 nm-thick active layer).