Achieving High Efficiency and Stability in Organic Photovoltaics with a Nanometer-Scale Twin p–i–n Structured Active Layer

High Resolution Image Download MS PowerPoint Slide In pursuing high stability and power conversion efficiency for organic photovoltaics (OPVs), a sequential deposition (SD) approach to fabricate active layers with p–i–n structures (where p, i, and n represent the electron donor, mixed donor:acceptor, and electron acceptor regions, respectively, distinctively different from the bulk heterojunction (BHJ) structure) has emerged. Here, we present a novel approach that by incorporating two polymer donors, PBDBT-DTBT and PTQ-2F, and one small-molecule acceptor, BTP-3-EH-4Cl, into the active layer with sequential deposition, we formed a device with nanometer-scale twin p–i–n structured active layer. The twin p–i–n PBDBT-DTBT:PTQ-2F/BTP-3-EH-4Cl device involved first depositing a PBDBT-DTBT:PTQ-2F blend under layer and then a BTP-3-EH-4Cl top layer and exhibited an improved power conversion efficiency (PCE) value of 18.6%, as compared to the 16.4% for the control BHJ PBDBT-DTBT:PTQ-2F:BTP-3-EH-4Cl device or 16.6% for the single p–i–n PBDBT-DTBT/BTP-3-EH-4Cl device. The PCE enhancement resulted mainly from the twin p–i–n active layer’s multiple nanoscale charge carrier pathways that contributed to an improved fill factor and faster photocurrent generation based on transient absorption studies. The PBDBT-DTBT:PTQ-2F/BTP-3-EH-4Cl film possessed a vertical twin p–i–n morphology that was revealed through secondary ion mass spectrometry and synchrotron grazing-incidence small-angle X-ray scattering analyses. The thermal stability ( T 80 ) at 85 °C of the twin p–i–n PBDBT-DTBT:PTQ-2F/BTP-3-EH-4Cl device surpassed that of the single p–i–n PBDBT-DTBT/BTP-3-EH-4Cl devices (906 vs 196 h). This approach of providing a twin p–i–n structure in the active layer can lead to substantial enhancements in both the PCE and stability of organic photovoltaics, laying a solid foundation for future commercialization of the organic photovoltaics technology.