Abstract
Here we report on reorganization on heating of a perspective organic semiconductor poly(3-(2′-ethyl)hexylthiophene) (P3EHT). P3EHT is an analogue of a well-known poly(3-hexylthiophene) (P3HT), which has comparable optoelectronic properties and the advantage of a lower processing temperature. The processes of structural reorganization during heating of P3EHT have been explored with a combination of synchrotron X-ray scattering and ultrafast chip calorimetry. The signature of reorganization has been identified from an increase of d-spacing of 100 peak of the P3EHT unit cell. It was observed that reorganization operates during heating of P3EHT at conventional rates of a DSC experiment (i.e., at 10 deg/min), whereas it is largely suppressed at a heating rate of 100 deg/s. Despite the absence of reorganization at high heating rates the calorimetric curves exhibit pronounced double melting, which corroborates the model of the negative pressure building up during crystallization of semi-rigid chain polymers.
Highlights
The family of poly(3-alkylthiophenes) (P3ATs) has attracted significant interest over the last years due to the potential of these polymers for applications in the field of organic photovoltaics and fieldeffect transistors [1]
We showed that the details of the thermal behavior in the semirigid chain polymers can be efficiently analyzed if calorimetry is coupled in real time with a structure-sensitive technique such as X-ray scattering [9,10]
It can be seen that the unit cell of poly(3-(2′-ethyl) hexylthiophene) (P3EHT) does not change in the studied temperature range, the diffraction peaks at 60 °C become sharper, the fact that reflects larger crystal size and higher crystal perfection
Summary
The family of poly(3-alkylthiophenes) (P3ATs) has attracted significant interest over the last years due to the potential of these polymers for applications in the field of organic photovoltaics and fieldeffect transistors [1]. Among these polymers poly(3-hexylthiophene) (P3HT) has become the classical electron-donor system for several optoelectronic applications [2]. Despite its advantages such as high charge mobility P3HT has a drawback of having relatively high processing temperature related to its melting and glass transitions. Processing of the active layers of the optoelectronic devices requires annealing at high temperature followed by quenching that can result in generating thermodynamically metastable states. The details of the thermal behaviour of P3EHT and in particular its possible structural reorganization during heating should be carefully studied in order to be able to optimize the post-processing protocols of the active layers of photovoltaic devices
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