Role of ZnO Nanoparticles in the Electron Transport Layer of Fullerene and Non‐Fullerene Organic Solar Cells

ABSTRACT In this study, the properties of the electron transport layer (ETL) were improved by doping with zinc oxide (ZnO) nanoparticles (NPs) in a PFN solution. The organic solar cells (OSCs) were entirely fabricated and tested under regular atmospheric conditions by using active materials composed of fluorene ( F ) and diketopyrrolopyrrole ( DPP ) monomers called PFDPP‐2 copolymer, combined with poly(3‐hexylthiophene) ( P3HT ), and synthesized with 0.075% catalyst and PC 71 BM in a fullerene ternary system. P3HT and PFDPP‐2 polymers were synthesized by direct arylation polymerization. Additionally, a non‐fullerene binary system based on (PBDB‐T‐2F [ PM6 ]:BTP‐4Cl [ Y7 ]) was also analyzed. The solar devices based on this binary system, with ZnO NPs‐doped in the ETL layer, adopted the structure glass/ITO/PEDOT:PSS/ PM6 : Y7 /PFN:ZnO NPs/FM. Field's metal (FM) is a eutectic alloy used as a top electrode, deposited vacuum‐free. In contrast, the ternary system was configured with glass/ITO/PEDOT:PSS/ P3HT : PFDPP‐2 :PC 71 BM/PFN:ZnO NPs/FM. In the ternary system, a 39.9% improvement in current density (J sc ) was observed upon doping with ZnO NPs, achieving a maximum power conversion efficiency (PCE) of 4.02%, 5.5% more with respect to the ternary reference and 24.8% considering only P3HT in the active layer. A similar behavior was observed in binary solar cells, resulting in a 51.8% increase in J sc compared to the reference cell without ZnO NPs. For the non‐fullerene OSCs, the maximum PCE of 11.84% was achieved, representing a 2.7% improvement compared to the reference binary system without ZnO NPs. Regarding stability, both systems (binary and ternary) maintained their transmission bands partially during the first 200 h of operation, indicating a significant improvement in the stability of both devices. However, in P3HT : PFDPP‐2 :PC 71 BM cells, PCE decreased by 11% after 400 h, whereas in PM6 : Y7 cells, stability improved by 5% under the same conditions.