New Insights into the Molecular Dynamics of P3HT:PCBM Bulk Heterojunction: A Time-of-Flight Quasi-Elastic Neutron Scattering Study

Abstract

The molecular dynamics of organic semiconductor blend layers are likely to affect the optoelectronic properties and the performance of devices such as solar cells. We study the dynamics (5-50 ps) of the poly(3-hexylthiophene) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) blend by time-of-flight quasi-elastic neutron scattering, at temperatures in the range 250-360 K, thus spanning the glass transition temperature region of the polymer and the operation temperature of an OPV device. The behavior of the QENS signal provides evidence for the vitrification of P3HT upon blending, especially above the glass transition temperature, and the plasticization of PCBM by P3HT, both dynamics occurring on the picosecond time scale. TOC GRAPHICS Organic photovoltaic (OPV) devices have attracted a keen interest over the past decade for their potential low-cost, lightweight , flexibility and ease of use and processing. In contrast to inorganic solar cells, the photocurrent generation results from two consecutive processes Recently, a few computational studies attempted to capture the impact of the D-A microstructure by using molecular dynamic simulations as an initial structure to study charge separation. 7

Quantitative Analysis of the Molecular Dynamics of P3HT:PCBM Bulk Heterojunction

“…In a previous study, 12 we probed the local dynamics of a blend of regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) and Phenyl-C61-butyric acid methyl ester (PCBM) at a has been estimated to be between 10 and 25 wt% by various groups 2,9,13-14 and the model of the microstructure comprising solely a neat polymer and a neat fullerene phase has been ruled out experimentally in the favour of a three phase model with the fullerene being mixed with the polymer in the amorphous domain. 2 Phase separation is not achievable reachable within accessible time scales using fully atomistic MD simulations, thus the signal is reconstructed from the following three phases studied separately: crystalline P3HT, crystalline PCBM and the amorphous mixture leading to an overall PCBM loading of 50 wt%.…”

“…All the collection runs were carried out for 50 ns with a time step of 2 fs in NPT ensemble using a The simulation shows that the motions of some degrees of freedoms lie lower in energy than the experimental energy window of the IN6 spectrometer. 12 Thus, these motions are too slow to be resolved by the IN6 spectrometer and so are considered as elastic. Other motions lie higher in energy than the experimental energy window of the spectrometer.…”

Neutron Spectroscopy: An Under‐Utilised Tool for Organic Electronics Research?

“…[19,20] Thegroup used selective deuteration of the P3HT side chains in order to isolate and identify the different motions within their samples.T he results were in agreement with those of Paternó et al already discussed in Section 3.1. [19,20] Thegroup used selective deuteration of the P3HT side chains in order to isolate and identify the different motions within their samples.T he results were in agreement with those of Paternó et al already discussed in Section 3.1.…”

“…Thestudy of P3HT/PCBM blends was also undertaken by Guilbert et al and reported in two related publications. [19,20] Thegroup used selective deuteration of the P3HT side chains in order to isolate and identify the different motions within their samples.T he results were in agreement with those of Paternó et al already discussed in Section 3.1. In addition to the frustrated P3HT motions,G uilbert and co-workers discovered that the polymer also imparted ap lasticising effect on the PCBM portion of the blend, which was especially apparent above the glass transition temperature of the polymer, [19] across all experimentally accessible timescales (5-50 ps).…”

“…[19,20] Thegroup used selective deuteration of the P3HT side chains in order to isolate and identify the different motions within their samples.T he results were in agreement with those of Paternó et al already discussed in Section 3.1. In addition to the frustrated P3HT motions,G uilbert and co-workers discovered that the polymer also imparted ap lasticising effect on the PCBM portion of the blend, which was especially apparent above the glass transition temperature of the polymer, [19] across all experimentally accessible timescales (5-50 ps). TheQ ENS experiment was then used to validate their molecular dynamics simulations.T his allowed the group to more confidently extrapolate their theoretical model to timescales 3o rders of magnitude longer then the measured data (up to 50 ns), elucidating information that would not otherwise be accessible experimentally.…”