Tris-homoleptic cyclometalated Ir(III) complexes based on oligothiophene-derived ligands as electron donors for organic solar cells

Herein, two octahedral homoleptic tris-Ir(III) complexes namely Py3T3Ir and Py5T3Ir are designed from pyridine/oligothiophene hybridized cyclometalated ligands with different conjugation lengths. Py5T3Ir with enlarged conjugation shows bathochromic absorption, strengthened absorptivity in longer-wavelength region and lower-lying energy levels compared to Py3T3Ir. Moreover, Py3T3Ir bearing small-sized backbones presents stronger triplet characteristic with boosted phosphorescence and prolonged exciton lifetimes. Blending ZY-4Cl acceptor to construct all-small-molecule organic solar cells, Py5T3Ir performs evidently increased power conversion efficiency of 8.62% than 3.04% of Py3T3Ir. The pronounced improvement in photovoltaic performance is originated from the advantageous carrier dynamics and superior blend morphology. Our results indicate coordinated Ir complexes are expected as potential photovoltaic materials by judicious molecular design.