Sustainable processing solvents, photoactive materials, and scalable manufacturing will play a key role in commercializing printed organic photovoltaics (OPVs). The record-breaking pioneering OPV reports have done an outstanding job in accelerating the discovery of champion photoactive materials and device engineering practices; however, these works predominantly involve health-hazardous halogenated processing solvents/additives and non-scalable thin-film coating methods. Herein, large-area slot-die-manufactured OPV cells from eco-friendly halogen-free solvents and synthetically scalable materials are showcased. All the four layers; electron transport layer (SnO2), cathode interlayer (PDIN-H), bulk-heterojunction (BHJ, PTQ-10:BTP-4F-12), and hole transport layer [poly(3,4-ethylenedioxythiophene):polystyrene sulfonate) (PEDOT:PSS] are slot-die-coated in air. A non-halogenated co-solvent mixture of toluene and 2-methyl tetrahydrofuran is presented as an optimal processing solvent to realize the high-quality thin films of PTQ10:BTP-4F-12. The unencapsulated champion solar cells characterized in ambient conditions (RH = 30%, T = 22 °C) exhibit power conversion efficiencies (PCEs) of 12.1 and 17.8% under 1 Sun (100 mW/cm2) and indoor light-emitting diode lighting (580 μW/cm2) conditions, respectively. Additionally, PEDOT:PSS is successfully slot-die-coated atop BHJ by mitigating wettability challenges with the aid of surface treatment. The all four-layer slot-die-coated OPVs exhibit a PCE of 9.55%.
Traditionally, conjugated polymer syntheses have relied heavily on metal-catalyzed cross-coupling reactions. These cross-couplings require appropriately functionalized monomers, increasing the length and complexity of the overall synthesis; in addition, some of the commonly used reagents (e.g., trialkyltin chlorides) are highly toxic. Even after a polymer has been successfully prepared, residual metal impurities can also compromise its optoelectronic properties and performance in devices. As such, there is a demand for metal-free approaches to conjugated polymer synthesis. In this work, the indophenine reaction was used to polymerize thiophene and bifunctional isatin comonomers, with only sulfuric acid used as the catalyst. The structural influence of the comonomers was evaluated using different thiophenes and bifunctional isatins. The resulting polymers have very wide absorption bands that span the UV/vis/NIR regions, with optical bandgaps as low as 0.76 eV. The polymers show electrochromic behavior, as determined through spectroelectrochemical measurements.
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