Role of zinc oxide and carbonaceous nanomaterials in non-fullerene-based polymer bulk heterojunction solar cells for improved cost-to-performance ratio

Abstract

Cost-effective carbonaceous allotropes other than fullerene (i.e. carbon quantum dots or C-dots), ZnO nanoparticles and their nanocomposites were synthesized as alternatives to expensive fullerene in polymer-based bulk heterojunction solar cells. A facile microwave-assisted hydrothermal route was used to synthesize nanomaterials in a short time span along with inexpensive precursors to reduce the cost. Taking into account the cost-to-performance ratio, devices were fabricated in direct configuration as ITO/PEDOT:PSS/PFO-DBT:ZnO (or C-dots, Z@G, Z@C_dots)/Al followed by device optimization to obtain optimized device parameters. The devices exhibit significant short-circuit current density (J_sc), open-circuit voltage (V_oc) and power conversion efficiency (PCE). The best power conversion efficiency of 3.9% with J_sc of 14.8 mA cm⁻², V_oc of 0.82 V and fill factor of 32% was obtained with Z@C_dots as acceptor at active layer concentration of 40 mg ml⁻¹ and weight ratio of 1 : 1. In addition, the phase analysis of the active-layer interface demonstrates the better compatibility of the organic:organic phase (i.e. polymer:C-dots with a device PCE of 2.8%) as compared to the organic:inorganic phase (i.e. polymer:ZnO with a device PCE of 1.41%). Moreover, the best performance of the organic:hybrid phase (i.e. polymer:Z@C_dots with a device PCE of 3.9%) is due to the exploitation of properties of both organic and inorganic components on the same platform. C-dots as an acceptor give an overall power conversion efficiency of 2.8%, whereas Z@G resulted in an efficiency of 3.1%. A fullerene-based device gives an efficiency of 4.2% (just 0.3% more in comparison to Z@C_dots), but the difference in material cost is more than 50 times, which thus results in a significant improvement in the cost-to-performance ratio of a Z@C_dots-based device than a device using fullerene as an acceptor. Therefore, the developed carbonaceous nanomaterials act as potential acceptors in non-fullerene-based polymer solar cells for possible applications.