5 Conclusions
It is well established that the molecular packing and mesoscale morphology of
P3HT thin films play crucial roles in charge transport and device performance.
However, due to the complex microstructure of P3HT, comprising a network of
crystalline and amorphous domains, systematic investigation of the electrical
bottlenecks remains challenging. Besides the molecular orientation, the mesoscale
morphology is essential for charge transport, which is a complex multiscale process. Hence, different length scales must be considered. On a molecular scale, the
charge carrier mobility is affected by intramolecular and intermolecular charge
transport. The former is highly sensitive to the conformation of the chain and,
hence, to potential defects along the backbone that reduce the conjugation length.
The latter is defined by the strength of π–π interactions between adjacent chains. On
a macroscopic scale, the charge transport is determined by the interconnectivity of
the crystalline domains that are embedded in amorphous material. The introduction
of order and orientation in P3HT thin films over large surface areas allows a better
understanding of charge transport along different crystallographic directions and,
hence, charge transport bottlenecks can be identified.
To summarize, the control and understanding of morphology from the molecular
to the macroscopic scale is crucial for optical and electrical properties and therefore
also for device applications. P3HT, which has been the working horse of the
polymer electronic community for many years, can be regarded as a model semicrystalline polymer for more complicated, but also more efficient, polymers based
on other repeating units, e.g., donor–acceptor polymers.
Acknowledgements Financial support is acknowledged from the DFG within IRTG-1642,
SPP1355 and the Emmy Noether Programme. We thank F. Fischer, Dr. A. Ruff and M. Goll
from our group for support with Figures 2, 13 and 16.
References
1. Sirringhaus H, Brown PJ, Friend RH, Nielsen MM, Bechgaard K, Langeveld-Voss BMW,
Spiering AJH, Janssen RAJ, Meijer EW, Herwig P, de Leeuw DM (1999) Nature
401:685–688
2. Sirringhaus H, Kawase T, Friend RH, Shimoda T, Inbasekaran M, Wu W, Woo EP (2000)
Science 290:2123–2126
3. Yan H, Chen Z, Zheng Y, Newman C, Quinn JR, Do ¨tz F, Kastler M, Facchetti A (2009)
Nature 457:679–686
4. He Z, Zhong C, Su S, Xu M, Wu H, Cao Y (2012) Nat Photon 6:591–595
5. Bao Z, Dodabalapur A, Lovinger AJ (1996) Appl Phys Lett 69:4108–4110
6. Spano FC (2005) J Chem Phys 122:234701
7. Kim Y, Cook S, Tuladhar SM, Choulis SA, Nelson J, Durrant JR, Bradley DDC, Giles M,
McCulloch I, Ha C-S, Ree M (2006) Nat Mater 5:197–203
8. Salleo A (2007) Mater Today 10:38–45
9. Muthukumar M (2000) Eur Phys J E 3:199–202
78
K. Tremel and S. Ludwigs
It is well established that the molecular packing and mesoscale morphology of
P3HT thin films play crucial roles in charge transport and device performance.
However, due to the complex microstructure of P3HT, comprising a network of
crystalline and amorphous domains, systematic investigation of the electrical
bottlenecks remains challenging. Besides the molecular orientation, the mesoscale
morphology is essential for charge transport, which is a complex multiscale process. Hence, different length scales must be considered. On a molecular scale, the
charge carrier mobility is affected by intramolecular and intermolecular charge
transport. The former is highly sensitive to the conformation of the chain and,
hence, to potential defects along the backbone that reduce the conjugation length.
The latter is defined by the strength of π–π interactions between adjacent chains. On
a macroscopic scale, the charge transport is determined by the interconnectivity of
the crystalline domains that are embedded in amorphous material. The introduction
of order and orientation in P3HT thin films over large surface areas allows a better
understanding of charge transport along different crystallographic directions and,
hence, charge transport bottlenecks can be identified.
To summarize, the control and understanding of morphology from the molecular
to the macroscopic scale is crucial for optical and electrical properties and therefore
also for device applications. P3HT, which has been the working horse of the
polymer electronic community for many years, can be regarded as a model semicrystalline polymer for more complicated, but also more efficient, polymers based
on other repeating units, e.g., donor–acceptor polymers.
Acknowledgements Financial support is acknowledged from the DFG within IRTG-1642,
SPP1355 and the Emmy Noether Programme. We thank F. Fischer, Dr. A. Ruff and M. Goll
from our group for support with Figures 2, 13 and 16.
References
1. Sirringhaus H, Brown PJ, Friend RH, Nielsen MM, Bechgaard K, Langeveld-Voss BMW,
Spiering AJH, Janssen RAJ, Meijer EW, Herwig P, de Leeuw DM (1999) Nature
401:685–688
2. Sirringhaus H, Kawase T, Friend RH, Shimoda T, Inbasekaran M, Wu W, Woo EP (2000)
Science 290:2123–2126
3. Yan H, Chen Z, Zheng Y, Newman C, Quinn JR, Do ¨tz F, Kastler M, Facchetti A (2009)
Nature 457:679–686
4. He Z, Zhong C, Su S, Xu M, Wu H, Cao Y (2012) Nat Photon 6:591–595
5. Bao Z, Dodabalapur A, Lovinger AJ (1996) Appl Phys Lett 69:4108–4110
6. Spano FC (2005) J Chem Phys 122:234701
7. Kim Y, Cook S, Tuladhar SM, Choulis SA, Nelson J, Durrant JR, Bradley DDC, Giles M,
McCulloch I, Ha C-S, Ree M (2006) Nat Mater 5:197–203
8. Salleo A (2007) Mater Today 10:38–45
9. Muthukumar M (2000) Eur Phys J E 3:199–202
78
K. Tremel and S. Ludwigs