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.