We have designed and synthesized two low bandgap conjugated copolymers containing alternating meta-fluoro-p-alkoxyphenyl-(m-FPO-) or p-fluoro-m-alkoxyphenyl-(p-FPO-) substituted benzodithiophenes-co-benzooxadiazole (BO), named PBO-m-FPO and PBO-p-FPO. The properties, including UV−vis absorption, charge mobility and photovoltaic performance of the two polymers have been intensively investigated. The results indicated that the introduction of fluorine atom at m, p positions of phenyl substituted benzodithiophene unit hardly affected their absorption spectra and highest occupied molecular orbital (HOMO) level. However, the two polymers showed different photovoltaic properties. Power conversion efficiencies (PCEs) based on the device structure of ITO/PEDOT:PSS/polymer:PC 71 BM/ Ca/Al demonstrated a large distinction (5.9% for PBO-m-FPO vs 2.8% for PBO-p-FPO) at optimal weight ratio. When replacing the Ca layer with zirconium acetylacetonate (ZrAcac), using 3% 1,8-diiodooctane (DIO) as the active layer additive, the PCEs of PBO-m-FPO and PBO-p-FPO increased by 36% (8.0% vs 5.9%) and 85% (5.1% vs 2.8%), respectively. The active layer's mobilities, morphology and molecular packing resulted in a significant difference in short-circuit current density (J sc ) and fill factor (FF). ■ INTRODUCTIONPolymer solar cells (PSCs) based on bulk heterojunction (BHJ) have made tremendous advances toward commercialization. 1 Recently, the power conversion efficiencies (PCEs) of several polymers with single junction device have reached 11%. 2−5 As impressive and important renewable energy sources, PSCs have particular advantages such as simple device structure, lightweight, flexibility and low fabrication cost using simple ambient-condition solution or the roll-to-roll coating process. 6−8 Compared to inorganic-based solar cells, however, they still do not achieve the targeted 15% efficiency and satisfying lifetime, which is required for widespread commercialization. 9 Although optimizing the device fabrication 10,11 will improve photovoltaic performance, a promising candidate polymer with simple synthesis process is extremely in demand for broad applications of PSCs. 12 For high-performance PSCs, the ideal strategy is to design donor−acceptor (D−A) alternating molecular structure for BHJ solar cell, which can offer the unique feature of tuning the energy levels and the bandgap. 13 As well-known, PCE is proportional to the open-circuit voltage (V oc ), short-circuit current density (J sc ), and fill factor (FF). So we can independently modulate D−A copolymers to obtain a lowlying the highest occupied molecular orbital (HOMO) energy

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This study presents an experimental study, including interfacial tension (IFT) measurements, sandpack flood tests, and microscopic studies, for investigating the effect of the addition of low molecular weight alcohols on heavy oil recovery during alkaline flooding. According to the IFT results, the addition of low molecular weight alcohols can be detrimental to IFT reduction for the alkaline/heavy oil system, due to the partitioning of the alcohol molecules at the oil−water interface reducing the interfacial space available for surfactant molecules. However, sandpack floods conducted with the addition of the low molecular weight alcohols show a marked improvement in oil recovery over the alkaline-only flooding. The incremental oil recovery increases with the alcohol chain length from methanol to n-pentanol, but for the less water-soluble isoamyl alcohol and n-hexanol, the incremental oil recovery starts to decrease. The microscopic studies indicate that the alcohol additives can accelerate the reaction rate to produce large amounts of small water droplets inside the oil phase (W/O droplet flow), which reinforces the Jamin effect to improve sweep efficiency. Meanwhile, the addition of low molecular weight alcohols can also lead to the reduction in water-in-oil (W/O) emulsion viscosity, which contributes to the mobilization of trapped W/O emulsions, thereby improving the displacement efficiency of the alkaline flooding process.

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