UC Santa Barbara

Currently, silicon-based electronic devices dominate our technology landscape, significantly enhancing human life and realizing various technological possibilities. However, we are transitioning into an era where carbon-based organic electronic devices are gaining prominence. This shift was enabled by the groundbreaking discovery that polymers, previously regarded as insulators, can exhibit electrical conductivity. Since then, research has advanced significantly in the development of electronic devices utilizing conductive polymers and organic semiconductors. The semiconductor and conductive properties of these organic materials are heavily influenced by the degree of doping. While research has primarily focused on doping methods using various dopants, challenges related to stability and uniformity have emerged. To address these issues, conjugated polyelectrolytes (CPEs) with self-doping capabilities have been developed. These materials incorporate functional groups directly into the polymer structure, eliminating the need for external dopants. This advancement has enhanced their performance as both active layers and interface layers in organic devices, and their potential applications as biosensors are particularly promising. Despite progress in the field, a comprehensive understanding of complex donor-acceptor (D-A) type CPEs remains limited. This dissertation explores the design and application of D-A type self-doping CPEs. We systematically synthesized various D-A CPEs with different electron acceptor groups and investigated their optical and electronical properties. Our analysis revealed that these properties are predominantly influenced by the molecular structure, with experimental results aligning well with theoretical calculations. A notable finding was the significant variation in self-doping levels between two CPEs with similar energy levels. Simulation-based analysis of the protonation step's Gibbs free energy provided insights into this discrepancy, suggesting that such factors should be considered during the synthesis of self-doped CPEs. Furthermore, we evaluated the performance of these CPEs in organic electrochemical transistors (OECTs), a leading biosensor technology, to assess their practical applications.For OECTs, CPEs are considered ideal materials due to their high electrical and ionic conductivity. However, their efficiency can be limited by issues related to device performance. This study addresses these limitations through precise control of the molecular weight of CPE-BT-K. It was observed that charged CPEs with either excessively low or high molecular weights tend to form poorly ordered structures. This structural irregularity adversely impacts the transistor's performance by affecting the material's charge transfer behavior. Our analysis of CPE-OECT performance demonstrates that CPE-BT-K, with an optimized molecular weight, achieves the highest performance reported for OECTs to date. Beyond OECTs, there has been increasing interest in infrared organic photodetectors due to their broad applicability. However, high dark current remains a significant challenge for these devices. To tackle this issue, we explored the use of CPE-Ph as the interface layer in conjunction with cross-linking techniques. We found that the CPE-Ph thin film, when cross-linked, significantly reduces dark current. This improvement is attributed to effective energy level tuning and the insulating properties provided by GOPS localized on the surface. The resulting organic photodetector, with its ultra-low dark current, showcased exceptional performance and revealed that the activation energy of the dark current closely aligns with the band gap. This breakthrough addresses a major limitation of organic photodetectors, paving the way for enhanced device performance.