Customized Energy Down-Shift Using Iridium Complexes for Enhanced Performance of Polymer Solar Cells

The spectral absorption range of polymer solar cells can be efficiently increased by molecular compatibility and energy level control in the energy transfer system. However, there has been limited research on energy transfer materials for both amorphous and highly crystalline polymer active materials. For the first time, we developed customized iridium (Ir(III) complexes that are incorporated into the active materials, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexy)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7, amorphous) or poly(3-hexylthiophene) (P3HT, high crystalline) as energy donor additives. The Ir(III) complex with the 2-phenyl quinolone ligand increased the power conversion efficiency of the corresponding devices by approximately 20%. The enhancements are attributed to the improved molecular compatibility and energy level matching between the Ir(III) complex and the active material, long Forster resonance energy transfer radius, and high energy down-shift efficiency. Overall, we reveal Ir(III) complex additives for amorphous and highly crystalline polymer active materials. These additives would enable efficient energy transfer in polymer solar cells while retaining the desirable active layer morphology, thereby improving the light absorption and conversion.