Optimized Self-Assembled Monolayer Coverage using Molybdenum Trioxide-Modified Indium Tin Oxide for High-Performance Organic Solar Cells

Self-assembled monolayers (SAMs) have recently emerged as promising candidates for interfacial materials in organic photovoltaics (OPVs). However, the quality and integrity of SAM growth are significantly influenced by the surface morphology of indium tin oxide (ITO) substrates, which can compromise the performance and reproducibility of OPVs. To achieve controlled and high-quality SAMs assembly, this study presents an effective strategy to eliminate the sensitivity of SAM growth to polycrystalline ITO by depositing an amorphous molybdenum trioxide (MoO₃) thin layer on top. The application of MoO₃ can homogenize surface roughness and circumvent issues related to preferential grain orientation and distinct grain boundaries associated with ITO. This results in a more uniform and denser SAM coverage compared to direct growth on bare ITO. Consequently, the resulting OPVs based on the PM6/BTP-eC9 system exhibit an outstanding power conversion efficiency of 19.9% (certified at 19.3%), primarily due to reduced interfacial defects and optimized active layer morphology. More importantly, the introduction of MoO₃ between ITO and SAMs enhances the reproducibility of efficiency and the long-term stability of devices compared to those based solely on SAMs. This progress highlights the importance of refining the ITO surface microstructure to facilitate favorable SAM formation and subsequently construct high-performance OPVs.