Increased thermal stabilization of polymer photovoltaic cells with oligomeric PCBM

Abstract

The first oligomerisation of phenyl-C 61 -butyric acid methyl ester (PCBM) using a facile atom transfer radical addition polymerization (ATRAP) and its exploitation for organic photovoltaic devices is described.Oligo{(phenyl-C 61 -butyric acid methyl ester)-alt-[1,4-bis(bromomethyl)-2,5-bis(octyloxy)benzene]} (OPCBMMB) shows opto-electronic properties equivalent to those of PCBM but has a higher glass transition temperature. When mixed with various band gap semiconducting polymers, OPCBMMB delivers performances similar to PCBM but with an enhanced stabilization of the bulk heterojunction in photovoltaic devices on plastic substrates under thermal stress, regardless of the degree of crystallinity of the polymer and without changing opto-electronic properties.

Main‐chain alternating fullerene and dye oligomers for organic photovoltaics

“…The molecular weights of poly(fullerene)s are well known to be underestimated by GPC characterizations due to retention of C 60 in the column; for example, C 60 normally elutes after toluene . From the face value of the data in Fig.…”

“…Using chlorobenzene rather than THF as an eluent improves the elution of the materials slightly: PDPF is found to have M n = 2050 g mol −1 and Ð = 2.0, whereas PDPPCBM has M n = 3600 g mol −1 and Ð = 2.0, and while more accurate, these values remain doubtful. Prior work has shown the benefit of counting off consecutive peaks, assuming each represents the growth of the chain by one repeat unit, to estimate a more realistic molecular weight . In the case of PDPF, discrete shoulders show oligomers with 1–3 repeat units before reaching a peak of 4 monomers, indicating that M p = 5650 g mol −1 .…”

“…There are also clear benefits associated with using fullerenes in the main‐chain, rather than as pendent moieties, as this simplifies the chemistry and permits the formation of robust macromolecules with high C 60 contents. Recent developments have demonstrated that C 60 can be incorporated as a monomer into the main‐chain, either by atom transfer radical addition polymerizations, or by sterically controlled azomethine ylide cycloaddition polymerizations (SACAP), and both lead to greater variations in the electronic properties of C 60 . While the former gives regioregular polymers, the latter is of interest as it is metal‐free.…”

Oligo- and poly(fullerene)s for photovoltaic applications: Modeled electronic behaviors and synthesis

“…Theoretically, it is possible to produce only one type of isomer along the polymer chain, favoring the synthesis of materials with well‐defined electronic properties. This so‐called atom transfer radical addition polymerization (ATRAP) is facile, lends itself to the preparation of block copolymers, and can be extended to various C 60 derivatives such as phenyl‐C 61 ‐butyric acid methyl ester (PCBM) . However, only one polymer has been prepared using ATRAP, and the properties remain poorly understood.…”

Towards the synthesis of poly(azafulleroid)s: main chain fullerene oligomers for organic photovoltaic devices

“…Prior methods included Diels–Alder chemistry, methano‐bridges and an elegant tether‐directed pre‐modification of C 60 , but these also gave crosslinking, intractable products or required multi‐step preparative chemistry, respectively. An attempt to resolve this was made using atom transfer radical addition polymerization as the reaction is based on radical bis‐additions around just one C 60 1,4‐phenylic ring . One disadvantage of this system, though, was the high amounts of CuBr required, leading to metal impurities of which even trace amounts can be detrimental to device performances .…”