Effect of Alcohol Treatment on the Performance of PTB7:PC₇₁BM Bulk Heterojunction Solar Cells

Abstract

The effect of an environmentally friendly alcohol treatment on bulk heterojunction (BHJ) polymer solar cells using the low-bandgap copolymer based on thieno[3,4-b]thiophene-alt-benzodithiophene units and [6,6]-phenyl-C71-butyric acid methyl ester is systematically investigated. Different alcohols are tested, and besides the most commonly used methanol treatment, other alcohols such as ethanol, 2-propanol, and 1-butanol also improve the device performance to certain extents as compared to the untreated solar cells. Changes of the surface structure caused by the alcohol treatment are probed with atomic force microscopy, and the modification of inner film morphology is probed by time-of-flight-grazing incidence small-angle neutron scattering (TOF-GISANS). UV/vis measurements show that the thickness of all BHJ films remains unchanged by the different solvent treatments. Thus, the enhanced device performance induced by the alcohol treatments is correlated to the reconstruction of the inner film structures probed with TOF-GISANS and the modified energy levels at the interfaces between the BHJ layer and the aluminum electrodes, evident by the enhanced short-circuit current and open-circuit voltage of the I-V curves.

π‐Conjugated Donor Polymers: Structure Formation and Morphology in Solution, Bulk and Photovoltaic Blends

“…For example Guo and co-workers studied the effect of alcohol treatment on the morphology and performance of PTB7:PC71BM bulk heterojunction solar cells prepared with the solvent additive DIO. [161] Among methanol, ethanol, 2-propanol and 1-butanol in case of methanol the best performing devices were achieved in good agreements to earlier findings from the Heeger group. [162] Such best device performance was explained by the presence of the smallest structure sizes in the active layers after methanol treatment as determined from the GISANS data analysis.…”

Air-processed polymer tandem solar cells with power conversion efficiency exceeding 10%

“…According to our experimental results, View Article Online the devices treated with ethanol achieved slightly higher performances compared to the methanol treated references, although treatment with methanol was reported to achieve the best performance for the BDT-based polymers. 47 From a technical standpoint, treatment with ethanol would provide more space for large-scale production under various conditions such as processing at elevated temperatures. Treatment with an alcohol-based solvent also works well for devices in the inverted architecture (ITO/PEI/PTB7-Th:PC70BM/ MoOx/Ag).…”

Controlling additive behavior to reveal an alternative morphology formation mechanism in polymer : fullerene bulk-heterojunctions

“…16,17 Few removal processes have been proposed for residual solvents and additives, like vacuum processes and washing with highly volatile alcohols. [16][17][18][19] In spite of the effectiveness of these methods, none of them is applicable to large-scale coating methods. Thus, it is extremely important to understand the precise mechanism of additives on nanostructure formation in close coordination with solution thermodynamics, thin lm drying kinetics and the device performance, in order to design better ink formulations, eventually without additives.…”