Enhancing Performance of Blade-Coated ITO-Free OPV Devices for Efficient Indoor Light Harvesting

The development of indium tin oxide (ITO)-free organic photovoltaic (OPV) devices is crucial for advancing OPV technology. This study systematically investigated two types of ITO-free OPV devices for indoor light harvesting, with a focus on evaluating performance losses introduced by the blade coating technique. Compared to spin coating, blade coating results in poorer morphological characteristics of the active layer due to the suboptimal surface properties of ITO-free substrates. This restricts exciton dissociation and quantum efficiency. Additionally, the blade coating process is found to induce pinhole defects, thereby reducing the shunt resistance and increasing leakage current, which severely limits device performance under low-light. To address these issues, a surface modification strategy is developed for the substrate electrode, using either the pure donor or acceptor material from the active layer as a surface modifier. This approach effectively transforms the substrate electrode surface from hydrophilic to hydrophobic, thereby enhacing quantum efficiency, reducing pinhole density and leakage current, and improving the device performance under both high and low illumination conditions. Ultimately, using this strategy, large-area ITO-free OPV devices with an active area approaching 5 cm², which achieved a PCE of up to 20.1% under 4000 lux LED illumination are successfully demonstrated.