Charge Mobility and Transport Behavior in the Ordered and Disordered States of the Regioregular Poly(3-hexylthiophene)

Abstract

We theoretically analyze the charge-transfer behavior of regioregular poly(3-hexylthiophene) (rr-P3HT) by quantum mechanical (QM) and molecular dynamics (MD) methods. In particular, we clarify the effects associated with the respective contribution from the ordered and disordered regions. In the ordered regions, the typical value of the hole mobility along the intrachain route is about 1 cm(2) V(-1) s(-1), which is significantly larger than that along the pi-pi interchain route, approximately 10(-2) cm(2) V(-1) s(-1). Our results indicate that the main charge-transfer route within the P3HT ordered lamellae is along the intrachain direction instead of the interchain direction. Moreover, the calculated hole mobility of 10(-2) cm(2) V(-1) s(-1) along the pi-pi interchain route is consistent with the experimental data measured in the P3HT single fibril. In the disordered regions, we propose a crossing-point/bridging-chain model to describe the charge-transport routes. In this model, the hole mobility can reach the limit of around 10(-2) and 1 cm(2) V(-1) s(-1) when the charge takes the interchain route through the crossing points and the intrachain route along the bridging chains, respectively. As expected, the resultant mobility in the disordered state is strongly affected by the ratio of the amount of crossing points and bridging chains. When considering the presence of both ordered and disordered regions, the average overall charge mobility is mainly dominated by the charge transport in the disordered regions. The fact that some of the experimentally measured hole mobility by varying the molecular weight is limited to a maximum value of 10(-2) cm(2) V(-1) s(-1) is mainly due to the presence of more crossing points instead of the bridging chains in the disordered regions. With increasing the amount of the bridging chains in the disordered regions, one can expect an enhancement of the charge mobility, such as to the experimentally obtained high value of 0.1 cm(2) V(-1) s(-1).

Computationally connecting organic photovoltaic performance to atomistic arrangements and bulk morphology

“…The expected qualitative trend in mobility has been replicated; the mobility of the ordered morphology is significantly greater than the mobility within the disordered morphologies. Furthermore, the pipeline has quantitatively predicted that the improvement in mobility is around three orders of magnitude, in reasonable agreement with experimental investigations which have demonstrated a 1-2 order of magnitude increase in time-of-flight and field-effect mobilities depending on processing conditions, crystallinity and morphological structure [139][140][141][142]. Additionally, the absolute values of the mobilities reported here are in good quantitative agreement with experimental results.…”

“…A possible reason for this could be that, while qualitative agreement with experiment is common, quantitative agreement can vary significantly depending on the system studied. In general, calculated mobility values are often more accurate in small molecule systems where transfer integrals are averaged over, or an initial configuration is assumed [141,149,150]. Otherwise, these computational methods tend to overpredict the time-of-flight mobilities of material systems by two to six orders of magnitude, with more noticeable discrepancies for larger or more complex molecules with a greater quantity of physical conformations, such as polymer chains [75,80,151,152].…”

Structure and Morphology Control in Thin Films of Conjugated Polymers for an Improved Charge Transport

“…In contrast, the connection of "face-to-face", side-chains, different oriented crystalline regions and disordered regions are all larger barriers for hopping of carriers ( Figure 3I). Secondly, the tie chains connecting adjacent crystalline regions (Figure 1b) play an important role in decrease the transport barrier of carriers at grain boundary [43][44][45]. As known, the disordered regions between adjacent ordered domains limit the efficient transport of carriers.…”

“…As known, the disordered regions between adjacent ordered domains limit the efficient transport of carriers. Lan et al reported that there were three modes for chains in disordered regions between adjacent crystalline regions: extending, looping, and bridging chains [43]. In the disordered domains, the charge transport can occur in the interchain pathway by hopping between close enough chain ends/loops or in the intrachain pathway along the bridging chains.…”

Controlling PCBM aggregation in P3HT/PCBM film by a selective solvent vapor annealing

“…When represented by a two-dimensional model, it showed that a phase separated morphology with feature sizes smaller than ~50 nm could improve charge transport within and between the two phases and reduce bimolecular charge recombination [6]. In the case of P3HT/PCBM, the molecular ordering of rr-P3HT is concerned with photon absorption and hole transport [7][8][9], and the suitable size of phase separation is related to charge separation. In order to achieve an optimum morphology, many methods have been employed, including thermal annealing [10,11], solvent vapor annealing [12][13][14], mixed solvent [15,16], introduction of additives [17,18] and so on.…”