Impact of additive residue on the photodegradation of high performance polymer solar cells

Solvent additives are indispensable to achieve highly efficient organic solar cells. The additive residue is unavoidable especially when the devices are prepared at room temperature and atmospheric pressure. In this paper, we introduce 1,10-diiododecane (DID) as the additive, which has high boiling point, and investigate the effects of additive residue on the photodegradation of organic materials and photoelectric properties of solar cells after light illumination. The iodine from the residue of DID in the active layer could be confirmed by X-ray photoelectron spectroscope (XPS) measurements. Structural changes in the films upon illumination are probed using Fourier Transform Infrared Spectrometer (FTIR). The residual DID is found to dramatically decrease the photostability of the active layer and device performance under light illumination compared with those without additive residue, which are exemplified in current densityevoltage (J-V) and electrochemical impedance measurements. Furthermore, the absorption of the film with additive residue is unchanged after light illumination, indicating that the conjugation of the polymer is not affected by the residue. (C) 2017 Elsevier B.V. All rights reserved.