Synergetic Effect of the Iridium Complex for Morphology Optimization in Efficient and Thermally Stable Polymer Solar Cells

Active layer morphology is one of the crucial factors for achieving excellent device performance in polymer solar cells. Recently, solid additives have drawn great attention due to their great potential in morphology control, but a detailed explanation about the working mechanism of solid additive systems is still lacking. In this work, we provided an iridium complex-based solid additive (Ir-OH) to control the morphology and crystallinity of the photoactive layer by utilizing the synergetic effect of dual additives 1-chloronaphthalene and Ir-OH. The morphology of the devices with dual additives exhibited appropriate phase separation and domain size, which provided more continuous pathways for charge transport and also exhibited condensed pi-pi stacking and fine molecular ordering of photoactive materials, resulting in enhanced charge collection probability. Consequently, the treatment of dual additives exhibited enhanced power conversion efficiency (PCE) with enhanced exciton dissociation, charge collection, and reduced bimolecular recombination. In addition, we found that the device with dual additives exhibited strong thermal stability under a constant heat treatment at 130 degrees C, and the device performance retained 65% during 24 h, showing an improved PCE of 13.89%. We expected that the favorable morphology of active materials in metal complexes can suppress thermal degradation and lead to improved device performance.