Extending Exciton Diffusion Length via an Organic‐Metal Platinum Complex Additive for High‐Performance Thick‐Film Organic Solar Cells

The long exciton diffusion length ( L D ) plays an important role in promoting exciton dissociation, suppressing charge recombination, and improving the charge transport process, thereby improving the performance of organic solar cells (OSCs), especially in thick‐film OSCs. However, the limited L D hinders further improvement in device performance as the film thickness increases. Here, an organic‐metal platinum complex, namely TTz‐Pt, is synthesized and served as a solid additive into the D18‐Cl:L8‐BO system. The addition of TTz‐Pt enhanced the crystallinity of blends, reduced energy disorder, and trap density, and decreased non‐radiative recombination and exciton binding energy, which is conducive to prolonging the L D in the TTz‐Pt‐treated film, thereby facilitating the exciton dissociation and charge transport process along with inhibiting the charge recombination. Consequently, the TTz‐Pt‐treated D18:L8‐BO:IDIC device (100 nm) exhibits a champion power conversion efficiency (PCE) of 20.12% (certified as 19.54%), one of the highest PCEs reported for OSCs to date. Remarkably, a record‐breaking PCE of 18.84% is yielded for the active layer thickness of 300 nm. Furthermore, the TTz‐Pt exhibits superior universality in improving the performance of OSCs. This work provides a simple and universal approach to extending L D by introducing an organic‐metal platinum complex as a solid additive to achieve highly efficient thick‐film OSCs.