A dual-additive strategy based on a π-conjugated thiazolyl-azo molecule and carbon nanotubes for efficient inverted organic solar cells

Abstract

Further improvements in organic solar cells (OSCs) performance focus on enhancing molecular packing, facilitating charge transport, and reducing recombination processes within the active layer. Herein, a dual-additive system consisting of a 2-(2-Thiazolylazo)-p-cresol (TAC) and multi-walled carbon nanotubes (MWCNTs) was incorporated into poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]:[6, 6] -Phenyl-C₆₁-butyric acid methyl ester (PCDTBT:PC₆₁BM) bulk heterojunction (BHJ) to simultaneously modify their morphological and electronic properties. The incorporation of TAC and MWCNTs provides a synergistic effect that improves molecular packing, enhances the donor/acceptor interfacial morphology, and creates continuous pathways for charge transport throughout the active layer. Structural, optical, electrical, and photovoltaic investigations demonstrated that the developed active layers exhibit stronger absorption in the visible region, reduced photoluminescence (PL) intensity, enhanced charge-carrier mobility, and more efficient collection of photogenerated charges with lower recombination losses. The optimized quaternary device delivered a power conversion efficiency (PCE) of 8.63 ± 0.13%, corresponding to an enhancement of approximately 42.6% relative to the pristine device 6.05 ± 0.01%, together with simultaneous improvements in the open-circuit voltage (V_OC), short-circuit current density (J_SC), and fill factor (FF). The enhanced device performance results from the combined influence of TAC and MWCNTs, which improves molecular packing, introduces efficient charge transport pathways, and promotes effective exciton dissociation and charge collection. In conclusion, this work establishes an effective dual-additive approach for enhancing the performance of OSCs. The findings also provide a deeper understanding of the combined role of π-conjugated molecular additives and conductive carbon nanostructures in the design of efficient OSCs.