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Molecular packing and electronic processes in amorphous-like polymer bulk heterojunction solar cells with fullerene intercalation.

Xiao T, Xu H, Grancini G, Mai J, Petrozza A, Jeng US, Wang Y, Xin X, Lu Y, Choon NS, Xiao H, Ong BS, Lu X, Zhao N - Sci Rep (2014)

Bottom Line: In this work we carried out a systematic investigation on a high PV efficiency (>6%) BHJ system consisting of a newly developed 5,6-difluorobenzo[c] thiadiazole-based copolymer, PFBT-T20TT, and a fullerene derivative.Furthermore, we extracted the hole mobility based on the space limited current (SCLC) model and found that more efficient hole transport is achieved in the PFBT-T20TT:fullerene BHJ as compared to pure PFBT-T20TT, showing a different trend as compared to the previously reported highly crystalline polymer:fullerene blend with a similar intercalation manner.Our study correlates the fullerene intercalated polymer lamella morphology with device performance and provides a coherent model to interpret the high photovoltaic performance of some of the recently developed weakly-ordered BHJ systems based on conjugated polymers with branched side-chain.

View Article: PubMed Central - PubMed

Affiliation: Department of Electronic Engineering, Chinese University of Hong Kong, New Territories, Hong Kong.

ABSTRACT
The interpenetrating morphology formed by the electron donor and acceptor materials is critical for the performance of polymer:fullerene bulk heterojunction (BHJ) photovoltaic (PV) cells. In this work we carried out a systematic investigation on a high PV efficiency (>6%) BHJ system consisting of a newly developed 5,6-difluorobenzo[c] thiadiazole-based copolymer, PFBT-T20TT, and a fullerene derivative. Grazing incidence X-ray scattering measurements reveal the lower-ordered nature of the BHJ system as well as an intermixing morphology with intercalation of fullerene molecules between the PFBT-T20TT lamella. Steady-state and transient photo-induced absorption spectroscopy reveal ultrafast charge transfer (CT) at the PFBT-T20TT/fullerene interface, indicating that the CT process is no longer limited by exciton diffusion. Furthermore, we extracted the hole mobility based on the space limited current (SCLC) model and found that more efficient hole transport is achieved in the PFBT-T20TT:fullerene BHJ as compared to pure PFBT-T20TT, showing a different trend as compared to the previously reported highly crystalline polymer:fullerene blend with a similar intercalation manner. Our study correlates the fullerene intercalated polymer lamella morphology with device performance and provides a coherent model to interpret the high photovoltaic performance of some of the recently developed weakly-ordered BHJ systems based on conjugated polymers with branched side-chain.

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2D GIWAXS patterns of (a) pure PFBT-T20TT film (b) 1:2 and (c) 1:4 PFBT-T20TT: PC71BM blend films, and (d-f) the corresponding 2D GISAXS patterns. (g–h) Intensity integrals versus /q/ of (g) GIWAXS and (h) GISAXS patterns for pure PFBT-T20TT and PFBT-T20TT:PC71BM blends in the mass ratio of 1:2 and 1:4. The integrals are taken over a polar range between 30° and 45°, as illustrated in (d).
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f2: 2D GIWAXS patterns of (a) pure PFBT-T20TT film (b) 1:2 and (c) 1:4 PFBT-T20TT: PC71BM blend films, and (d-f) the corresponding 2D GISAXS patterns. (g–h) Intensity integrals versus /q/ of (g) GIWAXS and (h) GISAXS patterns for pure PFBT-T20TT and PFBT-T20TT:PC71BM blends in the mass ratio of 1:2 and 1:4. The integrals are taken over a polar range between 30° and 45°, as illustrated in (d).

Mentions: To investigate the morphology and molecular packing in pure PFBT-T20TT and PFBT-T20TT: PC71BM blends, we carried out grazing-incidence wide-angle X-ray scattering (GIWAXS) (Figure 2(a–c)) measurements. The GIWAXS pattern of pure PFBT-T20TT thin film (Figure 2(a)) exhibits an intense peak along qz axis at q = 0.25 Å−1, indicating a preferential lamellar stacking in the surface normal direction with a lattice spacing of 25.13 Å. This so-called “edge-on” lamellar stacking was commonly observed in pure P3HT thin films35. However, in contrast to P3HT:PCBM blends, this lamellar ordering was not preserved in PFBT-T20TT:PC71BM blend thin films in mass ratios of 1:2 and 1:4, indicated by the disappearance of the lamellar peak in the corresponding GIWAXS patterns (Figure 2(b,c)). Only the amorphous PC71BM ring at q ≈ 1.3 Å−1 and monotonically decreasing scattering intensity from the origin were observed in Figure 2(b,c). The PC71BM ring is narrower in Figure 2(c), which is reasonable as the higher loading of PC71BM may lead to a bit better ordering in the amorphous PC71BM domains. Just from the GIWAXS patterns, we cannot tell whether the mixing of PFBT-T20TT and PC71BM gives rise to a randomly mixed molecular packing structure without lamellar ordering or the lamellar structure is still maintained while its corresponding peak moves to a smaller q region which was shadowed by the beam stop of the GIWAXS detector.


Molecular packing and electronic processes in amorphous-like polymer bulk heterojunction solar cells with fullerene intercalation.

Xiao T, Xu H, Grancini G, Mai J, Petrozza A, Jeng US, Wang Y, Xin X, Lu Y, Choon NS, Xiao H, Ong BS, Lu X, Zhao N - Sci Rep (2014)

2D GIWAXS patterns of (a) pure PFBT-T20TT film (b) 1:2 and (c) 1:4 PFBT-T20TT: PC71BM blend films, and (d-f) the corresponding 2D GISAXS patterns. (g–h) Intensity integrals versus /q/ of (g) GIWAXS and (h) GISAXS patterns for pure PFBT-T20TT and PFBT-T20TT:PC71BM blends in the mass ratio of 1:2 and 1:4. The integrals are taken over a polar range between 30° and 45°, as illustrated in (d).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4048884&req=5

f2: 2D GIWAXS patterns of (a) pure PFBT-T20TT film (b) 1:2 and (c) 1:4 PFBT-T20TT: PC71BM blend films, and (d-f) the corresponding 2D GISAXS patterns. (g–h) Intensity integrals versus /q/ of (g) GIWAXS and (h) GISAXS patterns for pure PFBT-T20TT and PFBT-T20TT:PC71BM blends in the mass ratio of 1:2 and 1:4. The integrals are taken over a polar range between 30° and 45°, as illustrated in (d).
Mentions: To investigate the morphology and molecular packing in pure PFBT-T20TT and PFBT-T20TT: PC71BM blends, we carried out grazing-incidence wide-angle X-ray scattering (GIWAXS) (Figure 2(a–c)) measurements. The GIWAXS pattern of pure PFBT-T20TT thin film (Figure 2(a)) exhibits an intense peak along qz axis at q = 0.25 Å−1, indicating a preferential lamellar stacking in the surface normal direction with a lattice spacing of 25.13 Å. This so-called “edge-on” lamellar stacking was commonly observed in pure P3HT thin films35. However, in contrast to P3HT:PCBM blends, this lamellar ordering was not preserved in PFBT-T20TT:PC71BM blend thin films in mass ratios of 1:2 and 1:4, indicated by the disappearance of the lamellar peak in the corresponding GIWAXS patterns (Figure 2(b,c)). Only the amorphous PC71BM ring at q ≈ 1.3 Å−1 and monotonically decreasing scattering intensity from the origin were observed in Figure 2(b,c). The PC71BM ring is narrower in Figure 2(c), which is reasonable as the higher loading of PC71BM may lead to a bit better ordering in the amorphous PC71BM domains. Just from the GIWAXS patterns, we cannot tell whether the mixing of PFBT-T20TT and PC71BM gives rise to a randomly mixed molecular packing structure without lamellar ordering or the lamellar structure is still maintained while its corresponding peak moves to a smaller q region which was shadowed by the beam stop of the GIWAXS detector.

Bottom Line: In this work we carried out a systematic investigation on a high PV efficiency (>6%) BHJ system consisting of a newly developed 5,6-difluorobenzo[c] thiadiazole-based copolymer, PFBT-T20TT, and a fullerene derivative.Furthermore, we extracted the hole mobility based on the space limited current (SCLC) model and found that more efficient hole transport is achieved in the PFBT-T20TT:fullerene BHJ as compared to pure PFBT-T20TT, showing a different trend as compared to the previously reported highly crystalline polymer:fullerene blend with a similar intercalation manner.Our study correlates the fullerene intercalated polymer lamella morphology with device performance and provides a coherent model to interpret the high photovoltaic performance of some of the recently developed weakly-ordered BHJ systems based on conjugated polymers with branched side-chain.

View Article: PubMed Central - PubMed

Affiliation: Department of Electronic Engineering, Chinese University of Hong Kong, New Territories, Hong Kong.

ABSTRACT
The interpenetrating morphology formed by the electron donor and acceptor materials is critical for the performance of polymer:fullerene bulk heterojunction (BHJ) photovoltaic (PV) cells. In this work we carried out a systematic investigation on a high PV efficiency (>6%) BHJ system consisting of a newly developed 5,6-difluorobenzo[c] thiadiazole-based copolymer, PFBT-T20TT, and a fullerene derivative. Grazing incidence X-ray scattering measurements reveal the lower-ordered nature of the BHJ system as well as an intermixing morphology with intercalation of fullerene molecules between the PFBT-T20TT lamella. Steady-state and transient photo-induced absorption spectroscopy reveal ultrafast charge transfer (CT) at the PFBT-T20TT/fullerene interface, indicating that the CT process is no longer limited by exciton diffusion. Furthermore, we extracted the hole mobility based on the space limited current (SCLC) model and found that more efficient hole transport is achieved in the PFBT-T20TT:fullerene BHJ as compared to pure PFBT-T20TT, showing a different trend as compared to the previously reported highly crystalline polymer:fullerene blend with a similar intercalation manner. Our study correlates the fullerene intercalated polymer lamella morphology with device performance and provides a coherent model to interpret the high photovoltaic performance of some of the recently developed weakly-ordered BHJ systems based on conjugated polymers with branched side-chain.

No MeSH data available.


Related in: MedlinePlus