Enhanced Vertical Charge Transport in a Semiconducting P3HT Thin Film on Single Layer Graphene

Abstract

The crystallization and electrical characterization of the semiconducting polymer poly(3‐hexylthiophene) (P3HT) on a single layer graphene sheet is reported. Grazing incidence X‐ray diffraction revealed that P3HT crystallizes with a mixture of face‐on and edge‐on lamellar orientations on graphene compared to mainly edge‐on on a silicon substrate. Moreover, whereas ultrathin (10 nm) P3HT films form well oriented face‐on and edge‐on lamellae, thicker (50 nm) films form a mosaic of lamellae oriented at different angles from the graphene substrate. This mosaic of crystallites with π–π stacking oriented homogeneously at various angles inside the film favors the creation of a continuous pathway of interconnected crystallites, and results in a strong enhancement in vertical charge transport and charge carrier mobility in the thicker P3HT film. These results provide a better understanding of polythiophene crystallization on graphene, and should help the design of more efficient graphene based organic devices by control of the crystallinity of the semiconducting film.

Elucidating the Effect of Interfacial Interactions on Crystal Orientations in Thin Films of Polythiophenes

“…Figure e demonstrates that the (020) reflection around q z = 16.7 nm –1 pointing along the b crystal axis lies normal to the graphene surface and confirms the existence of the face-on oriented crystals as well. Thus, the results in Figure c,e are in line with the previous studies on P3HT thin-film crystal orientation on graphene reported by Skrypnychuk et al − By contrast, the grazing-incidence WAXS pattern of P3BrHT with a thickness of 21 nm on graphene in Figure d shows the most intense (200) reflection of the triclinic P3BrHT crystal lattice located only parallel to the sample surface . An additional measurement (see Figure S1 in the Supporting Information) at an incident angle of 4.5°, which is close to Bragg’s condition for the (200) reflection, indicates no (200) reflection on the meridian and along with the results in Figure f proves the complete face-on crystal orientation in this sample.…”

Elucidating the Effect of Interfacial Interactions on Crystal Orientations in Thin Films of Polythiophenes

“…Figure e demonstrates that the (020) reflection around q z = 16.7 nm –1 pointing along the b crystal axis lies normal to the graphene surface and confirms the existence of the face-on oriented crystals as well. Thus, the results in Figure c,e are in line with the previous studies on P3HT thin-film crystal orientation on graphene reported by Skrypnychuk et al − By contrast, the grazing-incidence WAXS pattern of P3BrHT with a thickness of 21 nm on graphene in Figure d shows the most intense (200) reflection of the triclinic P3BrHT crystal lattice located only parallel to the sample surface . An additional measurement (see Figure S1 in the Supporting Information) at an incident angle of 4.5°, which is close to Bragg’s condition for the (200) reflection, indicates no (200) reflection on the meridian and along with the results in Figure f proves the complete face-on crystal orientation in this sample.…”

Reduced crystallinity and enhanced charge transport by melt annealing of an organic semiconductor on single layer graphene

“…This crystallite orientation has been shown to promote vertical charge transport in P3HT due to fast charge transport along the p stacking inside the crystallites, and by enabling the formation of a better interconnected charge pathway between crystallites inside the film. 18 We believe that the difference in crystallinity between the two films explains the higher mobility measured in the samples annealed at 240 1C, and it is consistent with previous studies of P3HT crystallinity and charge transport. 18 Here, we show that the charge carrier mobility in P3HT on graphene can be enhanced by more than 100% by annealing the film at higher temperatures (240 1C vs. 170 1C).…”

“…18 We believe that the difference in crystallinity between the two films explains the higher mobility measured in the samples annealed at 240 1C, and it is consistent with previous studies of P3HT crystallinity and charge transport. 18 Here, we show that the charge carrier mobility in P3HT on graphene can be enhanced by more than 100% by annealing the film at higher temperatures (240 1C vs. 170 1C). It is also worth noticing that the films studied here are slightly thicker than those previously used (85 nm vs. 50 nm) and that they display higher mobility.…”

Enhanced properties of photovoltaic devices tailored with novel supramolecular structures based on reduced graphene oxide nanosheets grafted/functionalized with thiophenic materials

“…As reported in Supporting Information Table S1, the contact angles of GO and rGO were 51.5 and 80.1 ° , respectively. Such a face‐on orientation was also reported in the literature . Indeed, the surface energy, which was in a direct correlation with the contact angle did not conspicuously affect the P3HT orientation.…”

Elucidating the Effect of Interfacial Interactions on Crystal Orientations in Thin Films of Polythiophenes

“…Figure e demonstrates that the (020) reflection around q z = 16.7 nm –1 pointing along the b crystal axis lies normal to the graphene surface and confirms the existence of the face-on oriented crystals as well. Thus, the results in Figure c,e are in line with the previous studies on P3HT thin-film crystal orientation on graphene reported by Skrypnychuk et al − By contrast, the grazing-incidence WAXS pattern of P3BrHT with a thickness of 21 nm on graphene in Figure d shows the most intense (200) reflection of the triclinic P3BrHT crystal lattice located only parallel to the sample surface . An additional measurement (see Figure S1 in the Supporting Information) at an incident angle of 4.5°, which is close to Bragg’s condition for the (200) reflection, indicates no (200) reflection on the meridian and along with the results in Figure f proves the complete face-on crystal orientation in this sample.…”

Reduced crystallinity and enhanced charge transport by melt annealing of an organic semiconductor on single layer graphene

“…This crystallite orientation has been shown to promote vertical charge transport in P3HT due to fast charge transport along the p stacking inside the crystallites, and by enabling the formation of a better interconnected charge pathway between crystallites inside the film. 18 We believe that the difference in crystallinity between the two films explains the higher mobility measured in the samples annealed at 240 1C, and it is consistent with previous studies of P3HT crystallinity and charge transport. 18 Here, we show that the charge carrier mobility in P3HT on graphene can be enhanced by more than 100% by annealing the film at higher temperatures (240 1C vs. 170 1C).…”

“…18 We believe that the difference in crystallinity between the two films explains the higher mobility measured in the samples annealed at 240 1C, and it is consistent with previous studies of P3HT crystallinity and charge transport. 18 Here, we show that the charge carrier mobility in P3HT on graphene can be enhanced by more than 100% by annealing the film at higher temperatures (240 1C vs. 170 1C). It is also worth noticing that the films studied here are slightly thicker than those previously used (85 nm vs. 50 nm) and that they display higher mobility.…”

Enhanced properties of photovoltaic devices tailored with novel supramolecular structures based on reduced graphene oxide nanosheets grafted/functionalized with thiophenic materials

“…As reported in Supporting Information Table S1, the contact angles of GO and rGO were 51.5 and 80.1 ° , respectively. Such a face‐on orientation was also reported in the literature . Indeed, the surface energy, which was in a direct correlation with the contact angle did not conspicuously affect the P3HT orientation.…”

Elucidating the Effect of Interfacial Interactions on Crystal Orientations in Thin Films of Polythiophenes

“…Figure e demonstrates that the (020) reflection around q z = 16.7 nm –1 pointing along the b crystal axis lies normal to the graphene surface and confirms the existence of the face-on oriented crystals as well. Thus, the results in Figure c,e are in line with the previous studies on P3HT thin-film crystal orientation on graphene reported by Skrypnychuk et al − By contrast, the grazing-incidence WAXS pattern of P3BrHT with a thickness of 21 nm on graphene in Figure d shows the most intense (200) reflection of the triclinic P3BrHT crystal lattice located only parallel to the sample surface . An additional measurement (see Figure S1 in the Supporting Information) at an incident angle of 4.5°, which is close to Bragg’s condition for the (200) reflection, indicates no (200) reflection on the meridian and along with the results in Figure f proves the complete face-on crystal orientation in this sample.…”

Reduced crystallinity and enhanced charge transport by melt annealing of an organic semiconductor on single layer graphene

“…This crystallite orientation has been shown to promote vertical charge transport in P3HT due to fast charge transport along the p stacking inside the crystallites, and by enabling the formation of a better interconnected charge pathway between crystallites inside the film. 18 We believe that the difference in crystallinity between the two films explains the higher mobility measured in the samples annealed at 240 1C, and it is consistent with previous studies of P3HT crystallinity and charge transport. 18 Here, we show that the charge carrier mobility in P3HT on graphene can be enhanced by more than 100% by annealing the film at higher temperatures (240 1C vs. 170 1C).…”

“…18 We believe that the difference in crystallinity between the two films explains the higher mobility measured in the samples annealed at 240 1C, and it is consistent with previous studies of P3HT crystallinity and charge transport. 18 Here, we show that the charge carrier mobility in P3HT on graphene can be enhanced by more than 100% by annealing the film at higher temperatures (240 1C vs. 170 1C). It is also worth noticing that the films studied here are slightly thicker than those previously used (85 nm vs. 50 nm) and that they display higher mobility.…”

Enhanced properties of photovoltaic devices tailored with novel supramolecular structures based on reduced graphene oxide nanosheets grafted/functionalized with thiophenic materials

“…As reported in Supporting Information Table S1, the contact angles of GO and rGO were 51.5 and 80.1 ° , respectively. Such a face‐on orientation was also reported in the literature . Indeed, the surface energy, which was in a direct correlation with the contact angle did not conspicuously affect the P3HT orientation.…”