Abstract
Organic photovoltaics (OPVs) are a promising next-generation solar energy technology, offering advantages such as mechanical flexibility, lightweight design, tunable optical bandgaps, and suitability for diverse light-harvesting applications. While notable progress has been made in power conversion efficiency and processing reproducibility for bulk heterojunction (BHJ) OPVs at the lab level, and layer-by-layer (LBL) fabrication techniques now achieve competitive efficiencies, important challenges still exist. Specifically, achieving long-term operational stability under ambient conditions, reducing reliance on costly noble metal electrodes, such as silver (Ag), and ensuring flexibility for application-specific device customization remain challenges that continue to hinder large-scale deployment and long-term commercial viability.
This thesis addresses these barriers by first addressing the sustainability and cost limitations associated with silver cathodes by investigating copper (Cu) as an alternative. Although direct Cu integration leads to notable optical and stability losses, detailed optical-electronic analysis reveals the origins of these degradations and enables the development of an optimized Ag/Cu bilayer cathode that reduces Ag usage by ~60% while restoring performance and improving device lifetime. The second study examines OPV performance under indoor light conditions through a systematic comparison of bulk heterojunction (BHJ) and layer-by-layer (LBL) architectures using an optimised ternary system. By tuning the donor-acceptor arrangement and sequential deposition in the LBL stack, improved voltage retention and reduced trap-assisted recombination are achieved, along with a PCE of 29.99% under indoor light, demonstrating the superior suitability of LBL devices for low-intensity illumination. Finally, to advance OPVs toward scalable production, the thesis develops a stable and reproducible OPV device stack reaching ~19% PCE that replaces the unstable C60:BCP ETL with the more robust polymeric ETL PDINN. This substitution delivers a 97% improvement in T80 under ambient conditions. The optimized PDINN-based OPV stack is further scaled via bar coating the active layer to fabricate large-area mini-modules with uniform, reproducible performance, demonstrating compatibility with high-throughput processing and industrial manufacturing.
This thesis highlights the multifaceted strategies required to advance OPV technologies toward real-world implementation, including cost-effective electrode integration, interface stabilization, and structural optimization for specific application environments. The insights and design principles presented herein provide valuable guidelines for the future development of both outdoor and indoor OPV systems, contributing to a broader field of stable, scalable, and efficient organic solar energy
harvesting.
