Configuration-dependent photovoltaic properties of diketopyrrolopyrrole (DPP) based Ir complexes for organic solar cells

Organometallic complexes with diverse spatial configurations have been rarely investigated in organic solar cells (OSCs). In this work, two octahedral cyclometalated Ir(III) complexes of bis-heteroleptic DPPTBzIr and tris-homoleptic DPPTBz3Ir are designed from a highly planar diketopyrrolopyrrole (DPP)-containing ligand DPPTBz. Upon coordination, gradually increased optical absorption was observed with the maximum molar extinction coefficient (ε) of 3.80×10⁴, 5.19×10⁴ and 1.39×10⁵ M^-1 cm^-1 for DPPTBz, DPPTBzIr and DPPTBz3Ir, respectively. Unexpectedly, owing to the large π-conjugation and strong intraligand donor-acceptor interactions from the cyclometalated DPPTBz ligand, no obvious triplet character is determined for the DPP-containing Ir complexes from both experimental and theoretical methods. When employed as electron donor materials for OSCs by blending with fused-ring electron acceptor N3, substantially improved power conversion efficiency (PCE) with average values from 0.74%, 2.2% to 3.41% are achieved for DPPTBz, DPPTBzIr and DPPTBz3Ir, respectively. The best photovoltaic performance for DPPTBz3Ir is originated from strengthened light harvest, suitable energy levels, manipulated blend morphologies and favorable carrier dynamics in the corresponding devices.