FTIR Study of the Impact of PC[60]BM on the Photodegradation of the Low Band Gap Polymer PCPDTBT under O₂ Environment

Abstract

The photo-degradation of the low band-gap polymer Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) during irradiation under white light (AM 1.5 conditions) has been studied in pristine polymer films as well as in blend films with [6,6]-Phenyl C61 butyric acid methyl ester (PC[60]BM). In order to gain insight into the degradation process, FTIR spectroscopy has been used to follow the evolution of different subunits of the polymer and to probe the chemical product formation. In contrast to other polymers, not the alkyl side chains but the π-conjugated system is preferentially oxidized during the first stages of degradation. Furthermore it has been shown that the subunits of the polymer backbone are differently affected by the degradation. Blending the polymer with PC[60]BM leads to a significantly larger impact on the stability of the cyclopentadiene group compared to the benzene ring of the benzothiadiazole group.

Impact of intentional photo-oxidation of a donor polymer and PC70BM on solar cell performance

“…This implies that new carbonyl structures are formed, most likely in different types of binding configurations. This assignment and the observed degradation are in agreement with the FT-IR results published by Chambon et al 19 for PC 60 BM thin films exposed to simulated sunlight and ambient air and the report of Dettinger et al 41 of changes in the FT-IR spectrum of PC 60 BM films degraded by exposure to simulated sunlight and O 2 .…”

Photodegradation of Si-PCPDTBT:PCBM active layer for organic solar cells applications: A surface and bulk investigation

“…The rapid degradation of the C70 moieties could be attributed to the radical scavenger property of the fullerene which is the target of the byproducts (radicals) from the polymer. The increase of absorbance of the polymer modes during the first step of exposure could be tentatively attributed to a structural reorganization, probably a change of conformation as recently proposed for C-PCPDTBT (the carbon analogue of the present polymer) which exhibited the same behavior [15]. Interestingly, this possible reorganization occurs within the first step of the UV-vis decay (Fig.…”

“…Therefore, resistant organic materials and a better understanding of the photooxidation mechanism are required. The photodegradation of various conjugated polymers or blends have been reported in the literature [9][10][11][12][13][14][15][16][17].…”

Side‐Chain Engineering for Enhancing the Properties of Small Molecule Solar Cells: A Trade‐off Beyond Efficiency

“…The initial density of photogenerated carriers (n(0)) and the effective second order recombination coefficient (τ B , see Table S9 in the SI) were calculated by fitting the corresponding time-dependence of the charge carrier density (Equation: [53] where γ is the time-independent parameter). [20,43,53,57,58] In addition, e , [53] where ε 0 is the electric constant and ε is the spatially averaged dielectric constant.). Besides, the bimolecular recombination prefactors β for the measured time scale are found to ranges from 1.25 × 10 −12 to 4.39 × 10 −13 cm 3 s −1 for BDTT-TR system, from 2.40 × 10 −12 to 5.84 × 10 −13 cm 3 s −1 for BDTT-O-TR system and from 9.87 × 10 −12 to 6.50 × 10 −13 cm 3 s −1 for BDTT-S-TR system.…”

“…[40,41] This has to be distinguished from intrinsic light-induced degradation as a severe limitation for device efficiency. [31,35,37,42,43] Therefore, it is important to develop facile approaches to improve both degradation mechanisms. Yang and co-workers have reported a series of polymers with different conjugated side chains on benzo[1,2-b:4,5-b′]-dithiophene (BDT) unit, and devices with a long alkyl-thieno [3,2-b]thiophene (alkyl-TT) substitution exhibited outstanding efficiency and thermal stability, which was attributed to the relatively small morphological changes of the active layer.…”