Enhanced photovoltaic performance of large-area organic solar cells via optimized two-step sequential doping with formic acid

Abstract

Over the past few decades, doping has emerged as a critical strategy for modulating the optoelectronic properties of organic semiconductors, such as organic field-effect transistors (OFETs) and organic solar cells (OSCs). Despite its versatility, the effective integration of dopants into bulk heterojunction (BHJ) frameworks remains a challenge. To address these limitations, this study investigates a two-step sequential p-type doping methodology utilizing formic acid, specifically applied to the PM6:Y6-based active layer in large-area OSCs. By precisely controlling the airbrush deposition speed, we demonstrate that a moderate two-step doping intensity (P-Medium) significantly refines both the morphological landscape and electrical behavior of the devices. Analytical results from electron paramagnetic resonance and ultraviolet-visible-near infrared spectroscopy confirm the formation of polaron states and illustrate the dopant's influence on molecular aggregation. This sequential approach facilitates a favorable face-on molecular orientation and minimizes surface roughness, thereby optimizing phase separation within the BHJ matrix. Consequently, the optimized P-Medium devices achieved a superior power conversion efficiency (PCE) of 16.12% (active area, 0.1 cm2), accompanied by enhanced charge-carrier dynamics. Our results suggest that this two-step sequential doping protocol offers a scalable and efficient pathwayto improve the performance of large-area organic photovoltaics.