Understanding Molecular And Photo-Assisted Doping of Organic Electronic Materials

Low-cost and reliable solar energy generation is crucial for establishing a sustainable energy future. Metal-halide perovskite solar cells have emerged as disruptive contenders in the solar market due to their low-temperature processability, abundant material composition, and solution processability. However, their short device lifespan remains a major obstacle to their economic competitiveness. The charge transport layers that interface with the perovskite active layer play a critical role in both the efficiency and lifespan of these solar cells. Extensive research on charge transport layers has led to significant improvements in efficiency and lifespan, with spiro-OMeTAD being the most extensively studied due to its excellent electrical properties. However, current doping methods for spiro-OMeTAD result in detrimental byproduct formation, impeding the scalability and lifespan of perovskite solar cells. This research aims to overcome these challenges by developing a novel doping process that effectively inhibits or eliminates the formation of these byproducts. The outcomes of this study have the potential to impact various fields relying on organic semiconductors, including field-effect transistors, photovoltaics, light-emitting diodes, and organic photo-detectors. It is expected to contribute significantly to improving the performance, scalability, and stability of organic semiconductor-based devices by enhancing doping efficiency, suppressing byproduct formation, achieving uniform doping, and enabling reliable and scalable processing. Furthermore, the funding from this project will support a laboratory experience for grade 10 and 11 high school students from a broad range of communities through the Applied Research Innovations in Science and Engineering (ARISE) program at New York University, providing valuable opportunities for research on perovskite solar cells. Our group has developed a new doping method utilizing a process gas and ultraviolet light to oxidize Spiro-OMeTAD solutions containing LiTFSI. This method improves film conductivity, durability, and reduces byproduct concentration. It has demonstrated efficacy in increasing conductivity of various organic polymer species, despite significant energy level barriers. However, the design criteria for dopant composition and energetics in fully solution-processed doping schemes are unclear. This project aims to understand the underlying mechanism of molecular and photo-assisted doping of organic electronics. Integrating engineering, chemistry, and physics, it offers a novel approach to tuning the properties of organic-based electronic materials, enhancing conductivity, uniformity, and stability. Our first aim explores the effects of cationic substitution of metal-TFSI salts on reaction pathways, byproduct concentration, and optoelectronic properties of cast films. The second aim probes the impacts of light intensity, wavelength, gas species, and solvent properties on doping efficiency in conjugated polymer systems with favorable and unfavorable energy level alignments. By investigating these mechanisms and their role in optoelectronic properties, we seek to improve doping efficiency, retention, uniformity, and expand the range of available dopant species in organic semiconducting films. These advancements will significantly contribute to perovskite solar cell technology, facilitating the transition from fossil fuels to clean energy and enabling cost-effective, scalable manufacturing techniques to meet increasing demand. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.