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.