ИСТИНА

Active layer of a bulk heterojunction solar cell generally represents a blend of p-type (conjugated polymer or small molecule) and n-type (fullerene derivative or non-fullerene acceptor) organic semiconductors. These materials undergo photochemical and thermal degradation under the realistic solar cell operation conditions. A thorough understanding of the most important degradation pathways might play a crucial role in improving the long-term stability of organic photovoltaics. We report a systematic study of three different groups of conjugated polymers (Fig. 1) exposed to continuous UV or white light illumination under anoxic conditions inside the glove box. Gel permeation chromatography (GPC) and fluorescent spectroscopy (FS) have been applied for the first time for monitoring the changes in the molecular weight characteristics of the polymers and reference monomer molecules and accumulation of defects in their thin films. Fig. 1. Molecular structure of investigated conjugated polymers We have revealed some important correlations between the chemical structures of the certain building blocks incorporated in the polymer chains and their photochemical stability. Light-induced cross-linking of the molecules proceeding presumably via [2+2]cycloaddition mechanism has been shown to be the main photochemical aging process. In case of polymers, this kind of cross-linking results in the rapid increase in the molecular weights and, finally, formation of insoluble products. This work was supported by the RFBR Grant No. 15-33-20566_mol_a_ved