Advancing organic photovoltaics : the role of dipole distance and acidity in perylene-diimide electron transport layers

Abstract

The electronic transport layer (ETL) based on perylene-diimide (PDI) has been widely demonstrated for efficient organic solar cells (OSCs). However, the effect of ETL materials on interfacial traps and energy losses remains understudied. This study investigates the effects of dipole distance on PDINN interface defects using three specifically designed weak acidic materials with varying carboxyl and hydroxyl group amounts. Among these, 3,5-dihydroxybenzoic acid (2OH), with moderate pH and high dipole distance, enhanced intermolecular forces with PDINN. This interaction boosted π–π stacking, enhanced ohmic contact with the active layer and Ag electrode. The P-2OH film exhibited a higher and more uniform potential distribution, suppressing charge recombination at the interface, reducing the trap density to 2.12 × 10¹⁶ cm³, and reducing the non-radiative loss ∆E₃ from 0.236 to 0.174 eV. Consequently, the energy loss decreased from 0.553 to 0.484 meV for the PM6: BTP-ec9/P-2OH device. Notably, a decent PCE of 19.1% is achieved for P-2OH (10 nm), and it impressively remains a power conversion efficiency (PCE) of 16.4% when thickness of P-2OH up to 50 nm. This work underscores the importance of hydroxyl and carboxyl groups in regulating the ETL to minimize energy loss and offers insights for developing thickness-insensitive interlayers for high-performance OSCs.