Effect of Miscibility and Percolation on Electron Transport in Amorphous Poly(3-Hexylthiophene)/Phenyl-C61-Butyric Acid Methyl Ester Blends

Abstract

Recent evidence has demonstrated that amorphous mixed phases are ubiquitous within mesostructured polythiophene-fullerene mixtures. Nevertheless, the role of mixing within nanophases on charge transport of organic semiconductor mixtures is not fully understood. To this end, we have examined the electron mobility in amorphous blends of poly(3-hexylthiophene) and phenyl-C(61)-butyric acid methyl ester. Our studies reveal that the miscibility of the components strongly affects electron transport within blends. Immiscibility promotes efficient electron transport by promoting percolating pathways within organic semiconductor mixtures. As a consequence, partial miscibility may be important for efficient charge transport in polythiophene-fullerene mixtures and organic solar cell performance.

Time-independent, high electron mobility in thin PC 61 BM films: Relevance to organic photovoltaics

“…In large PC 61 BM domains, one may expect similar electron transport as in pristine PC 61 BM, at least initially, until drifting electrons encounter a morphological structure of the donor that is unfavorable for a further electron drift. Comparing electron mobility in pristine film and in blend, we conclude that even at 1:1 (w/w) fullerene concentration, much higher than percolation threshold which is 15 % by volume fraction for PC 61 BM [30], the electron transport in blends is completely determined by obstacles for electron motion between fullerene domains rather than by the intrinsic mobility in PC 61 BM. The dramatic drop of the electron mobility in blends explains importance of the blend morphology and fullerene concentration for the carrier generation and recombination and consequently for the solar cell performance.…”

“…The hole mobility in PC 61 BM is much lower than the electron mobility [30][31][32], therefore holes may be considered as being stationary during the extraction time of electrons. This assumption is supported by the fact that the fast decay corresponds to 50% of the total field reduction measured by time-integrated photocurrent, which includes two equal contributions of electrons and holes.…”

Reducing burn-in voltage loss in polymer solar cells by increasing the polymer crystallinity

“…23,27 These larger, pure phases provide efficient charge transport throughout the bulk heterojunction towards the contacts. 23,47,48 An energetic offset between the amorphous and crystalline phases 26,49 likely causes electrons and holes to stay in their respective pure phases, in which they are transported very efficiently. 47 In such a three phase system, recombination is expected only if electrons and holes meet each other in the mixed phase.…”

A Study on the Correlation Between Structure and Hole Transport in Semi‐Crystalline Regioregular P3HT

“…[ 15 ] An amorphous phase, on the other hand, has been modeled by a regiorandom P3HT. [ 16 ] The differences in optical properties of rra-P3HT and rr-P3HT are assigned to a delocalization of electron wave functions along the planarized backbones (intra-chain), i.e., in the (001) direction, and along the π − π stacking (inter-chain), i.e., in the (020) direction, in the latter material. [ 17,18 ] Charge transport is more effi cient along these directions, as compared to the (100) direction where it is prohibited by the insulating hexyl side chain.…”