Scalable Fabrication of High-Efficiency and Stable Organic Solar Cells

Abstract

Human exploitation and consumption of fossil fuels have led to problems such as global warming and environmental degradation, prompting the search for clean, renewable, and low-cost green energy sources. Organic solar cells (OSCs) offer compelling advantages, including light weight, semi-transparency, solution processability, and compatibility with large-scale printing technologies, positioning them as promising candidates for next-generation renewable energy applications. Recent advances have propelled the highest power conversion efficiency (PCE) of OSCs toward 21%. However, the scalability of OSCs remains a challenge due to intrinsic limitations such as carrier-transporting kinetics in the organics and increased inhomogeneity and defect density in thin films during large-area production. The development of scalable fabrication methods for high-performance and stable OSCs represents a critical challenge in the transition from laboratory-scale devices to commercial photovoltaic applications. This thesis presents comprehensive research on three interconnected works to address the scalability and stability challenges in organic photovoltaics.

The first work addresses large-area fabrication challenges by developing a systematic approach to control drying front dynamics during film formation. Through optimized thermal and fluid management, this work achieves exceptional film uniformity across large coating widths while maintaining high device performance. Printed devices achieve a remarkable PCE of 19.47% under ambient conditions, which is the highest reported PCE for fully slot-die coated OSCs. The developed modeling framework provides a simplified evaluation system for industrial-scale coating processes.

The second work introduces a novel methodology employing azeotrope ink for scalable printing of self-assembled monolayers (SAMs) on ITO surfaces. The unique solvent combination with different polarities stabilizes SAM molecules while ensuring controllable evaporation rates, facilitating formation of high-quality hole-selective layers (HSL) compatible with fully printed p-i-n architecture devices. This approach overcomes traditional limitations in SAM fabrication scalability, enabling optimized devices to achieve impressive power conversion efficiencies of 18.89% for 0.04-cm² devices and 17.76% for 1-cm² devices, demonstrating the potential of azeotrope-assisted SAM printing as a scalable method for efficient OSC fabrication.

The third work systematically engineers SAM terminal groups to elucidate how interfacial molecular interactions between SAMs and bulk-heterojunction active layers govern device efficiency and thermal stability. SAMs incorporating naphthalene pendant groups exhibit significantly strengthened intermolecular interactions, effectively suppressing thermally induced morphological degradation under elevated temperatures. This interfacial molecular locking strategy enables PM6:BTP-eC9-based binary and ternary devices to achieve PCEs of 19.73% and 20.15%, respectively, while delivering a T90 operational lifetime of 150 hours under maximum power point tracking at 85°C, which represents an order-of-magnitude improvement compared to SAMs without pendant groups.

Collectively, these works establish a comprehensive framework for scalable OSCs manufacturing, addressing both fabrication uniformity and operational durability. The developed strategies demonstrate clear pathways toward industrial-scale production while maintaining the high efficiencies achieved in laboratory settings. This thesis contributes fundamental insights into large-area processing dynamics and interface engineering, providing practical solutions that advance organic photovoltaics toward commercial viability.

Date of Award	17 Aug 2026
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Hin Lap YIP (Supervisor) & Alex JEN (Co-supervisor)