In/Outdoor Organic Solar Cells with Effective Photon‐Harvesting by Introducing Light‐Amplification Layer with Eco‐Friendly QDs

Quantum dot organic solar cells (QD‐OSCs) have received considerable attention because of the luminescent property of QDs and the good miscibility due to the organic ligand in the shell. However, the use of Cd‐ or Pb‐based QDs is limited due to toxicity. Hence, Zn–Cu–In–S/ZnS QDs (ZQs) as nontoxic QDs are used in this study for the light‐amplification layer (LAL), consisting of sub‐donor (sub‐D, D18‐Cl) and QDs. The LAL applied between the hole transfer layer (HTL) and bulk heterojunction (BHJ, PM6:BTP‐eC9), ensurs effective photon amplification and high morphological stability. In particular, the ligands of ZQs constituting LAL interact with D18‐Cl and PM6:BTP‐eC9 to align molecular orientation and improve interface contact. The sub‐D/BHJ structure in which sub‐D and BHJ are introduced by layer‐by‐layer (LBL) coating method solves problems such as morphology degradation and stability degradation due to the complexity of existing ternary system. The sub‐D/BHJ, an effective ternary structure, shows a higher performance (17.06%) than the BHJ system (16.66%). Meanwhile, the LAL/BHJ shows not only the highest performance of 17.6% but also outstanding stability (93.6% after 1000 h). This study demonstrates effective energy harvesting through QDs and introduces an optimal QD‐OSCs structure strategy for high‐efficiency, high‐stability OSCs.