Pyridine-based additive optimized P3HT:PC61BM nanomorphology for improved performance and stability in polymer solar cells

Photovoltaic (PV) performance of bulk heterojunction polymer solar cells (BHJ PSCs) highly depends on the optoelectronic properties of the photoactive layer. In this regard, additives (solvent or solid) are considered as one of the versatile methods and key morphology directing agents for solution processed PV devices. Herein this contribution, we rationally utilize a new kind of pyridine-based solid additives (2-hydroxypyridine (2-DHP) and 2,4-dihydroxypyridine (2,4-DHP)) to manipulate and engineer the nanomorphology of the poly(3-hexylthiophene):[6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT:PC₆₁BM) photoactive system, that can influence the optoelectronic properties for enhanced performance in BHJ PSCs. The optical, electrical, morphological, surface, structural characteristics of the fabricated BHJ PSCs were systematically examined. The atomic force microscopy and X-ray photoelectron spectra measurements confirmed the structural reorganization, phase separation of polymer and fullerene domains resulting in the formation of well-ordered blend in the additive based devices. BHJ PSCs fabricated with P3HT:PC₆₁BM:2-DHP and P3HT:PC₆₁BM:2,4-DHP yielded a best power conversion efficiency (PCE) of 4.35% and 3.58%, respectively, which in contrast outperformed than the PCE obtained from P3HT:PC₆₁BM device (3.01%). The remarkably improved performance for P3HT:PC₆₁BM:2-DHP can be attributed to the enhanced short-circuit current density induced by the morphology optimization. Additionally, the devices fabricated with the solid additives (2-DHP and 2,4-DHP) exhibited improved air-stability due to the oxygen insensitivity of the functional groups present in the chosen additives. The pyridine and hydroxyl groups in 2-DHP and 2,4-DHP possibly form the intermolecular interactions with the photoactive components (P3HT/PC₆₁BM), contribute to the morphology optimization and subsequent PV performance enhancement in BHJ PSCs. It is believed that our findings can inspire and trigger further advanced research toward the design and development of stable and highly efficient BHJ PSCs by rationally choosing low-cost solid additives.