Isothermal crystallization of P3HT:PCBM blends studied by RHC

Demir

Geerlings

et al. 2012

Organic Photonics V

Self Cite

In this paper, a combined experimental and theoretical study was performed on the P3HT:PCBM system used in organic photovoltaics. Fast-scanning differential chip calorimetry, an advanced thermal analysis technique, was used to simulate the thermal annealing used in the production of P3HT:PCBM solar cells to increase the degree of crystallinity, and thus efficiency. The main advantage of this technique for stuying the thermal annealing are the very high rates of heating and cooling that can be used, up to 10 6 K.s -1 , permitting one to avoid crystallization during cooling. In parallel with the experimental study, the charge transfer between donor (P3HT) and acceptor (PCBM) at the interface is studied using density functional theory. The charge separation between donor and acceptor present for the ground state of the combined system, diminished when the first triplet was investigated. This was explained by the formation of a bridge state, formed after population by the LUMO with one electron. Such a molecular orbital can facilitate charge transfer.

Section: Experimental Annealing Studycontrasting

confidence: 61%

Section: Introductionmentioning

confidence: 99%

Looking at bulk-heterojunction organic photovoltaics from two viewpoints: morphology development and charge transfer

Demir

Geerlings

et al. 2012

Organic Photonics V

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“…The liquid nitrogen cooling of the RHC extends the temperature range over which the cooling is sufficiently fast to lower temperatures. In our previous study, it was shown that a ballistic cooling rate of more than 1500 K.min -1 is reached at the beginning of the cooling, which drops down to 750 K.min -1 around 60 °C, which is just above the T g of the blend [11].…”

Section: Resultsmentioning

confidence: 87%

“…The sample is heated to 275 °C, well above the melting temperature, for a short time, to remove the crystals and to erase the thermal history. An example of the temperature program is given in Reference [11]. For some isothermal annealing temperatures, the melting peak is preceded by a cold crystallization.…”

Section: Methodsmentioning

confidence: 99%

“…Investigating the glass transition and the isothermal crystallization kinetics starting from amorphous blends requires avoiding fast crystallization processes during heating and cooling [11], which can only succeed using fast-scanning techniques such as Rapid Heating Cooling Calorimetry (RHC). RHC, recently developed by TA Instruments, is a fast-scanning DSC permitting scanning rates of up to 2000 K.min -1 [12].…”

Section: Introductionmentioning

confidence: 99%

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Crystallization kinetics and morphology relations on thermally annealed bulk heterojunction solar cell blends studied by rapid heat cool calorimetry (RHC)

Demir

Bertho

et al. 2012

Organic Photonics V

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Optimizing the post-production annealing conditions of polymer:fullerene bulk heterojunction solar cells is vitally important, not only for fine-tuning the morphology -thus increasing the efficiency -but also for retaining the desired morphology during long-term operation. However, optimal conditions for annealing temperatures and times can only be chosen, once thermal transition temperatures and annealing kinetics of the blends are well-known. For instance, for systems with glass transition temperatures (T g ) lower than the maximum device operation temperature of 80°C, the mobility needed for morphology coarsening is present, leading to efficiencies decreasing in the course of time. Using advanced fast-scanning thermal analysis techniques, the formation of nuclei and growth of crystals during heating or cooling can be reduced or avoided, and thus, the fast crystallization processes occurring during annealing of the polymer:fullerene blends can be followed. In this study, non-isothermal and isothermal crystallization kinetics of the P3HT:PCBM (poly(3-hexyl thiophene: [6,6] -phenyl C 61 -butyric acid methyl ester) and P3HT:bis-PCBM blends are investigated and compared by using Rapid Heating Cooling Calorimetry (RHC).

Single‐step solution polymerization of poly(alkylene terephthalate)s: synthesis parameters and polymer characterization

Giol

Mele

et al. 2018

Polymer International

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Poly(alkylene terephthalate)s represent one of the most frequently used polymer classes worldwide. Well‐known examples include poly(ethylene terephthalate) (n = 2) and poly(butylene terephthalate) (n = 4). The conventional synthesis method for these polymers is based on melt polycondensation, a two‐stage process performed under harsh conditions that includes the synthesis of an intermediate prepolymer and the presence of a catalyst, which may induce toxicity issues. The present work reports on a straightforward single‐step solution polycondensation method performed under mild conditions and in the absence of a catalyst. A homologous series of poly(alkylene terephthalate)s (n = 5 − 10) of molar masses up to 20 000 g mol−1 and dispersity <2.4 was synthesized and characterized thoroughly. Great attention was given to the thermal properties assessment by using state‐of‐the‐art techniques and a highly sensitive prototype technique called rapid heat − cool DSC. Similar to melt‐synthesized polyesters, a particular odd − even trend of the thermal properties versus the number of methylene groups within the monomer unit was revealed. To the best of our knowledge, this is the first report covering a single‐step solution‐based polycondensation performed in the absence of a catalyst that results in highly reproducible polyesters possessing unaltered thermal properties compared to polyesters synthesized through industrially applied conventional routes. © 2017 Society of Chemical Industry