The effect of various solvent additives on the power conversion efficiency of polymer-polymer solar cells

다국어 초록 (Multilingual Abstract)

We investigated the effect of three different additives (1-chloronaphthalene, 1,8-diiodooctane, diphenylether) on the performance of polymer-polymer solar cells based on a BHJ blend consisting of poly[4,8-bis(5-(2-ethylhexyl) thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) as a donor and poly[[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)] (P(NDI2OD-T2)) as an acceptor. A direct comparison of the efficiency of the solar cells with and without additive indicated that the device using the additive exhibited slightly improved performance. However, the efficiency enhancement was not significant. The optimal ratio of additive differed depending on the properties of the additive. In addition, the performances of polymer-polymer solar cells were not significantly dependent on the type of additive. Identifying the optimal fabrication condition was critical for achieving the highest performance. It is known that the general role of an additive in polymer solar cells based on a BHJ active layer was to induce good phase separation between the donor and acceptor by morphology modification. However, grazing-incidence wide-angle X-ray scattering results showed that no significant morphology change in polymer-polymer active layer was caused by the additive. Rather, our modulated impedance spectroscopy study showed that the performance enhancement in polymer-polymer solar cells with additive was because of improved recombination properties rather than improvements in crystalline morphology.

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