Organic Electronics PCBM-Based n-Type Semiconductors

Unique chemistry and physics of fullerene (C₆₀) materials continue to stimulate advances in applied and fundamental science. Fullerenes are known as excellent electron acceptors and can be chemically modified to improve solubility in organic solvents. Such soluble fullerene derivatives are known as some of the best n-type organic semiconductors¹. Moreover, molecular heterojunctions made by covalently linking fullerenes with electron donating or photoactive macromolecules show promise as intrinsic p/n-type semiconductors and even artificial mimics of biological photosynthesis.² To help our customers achieve their research breakthroughs in organic electronics, Sigma-Aldrich^® is pleased to offer a line of high quality functionalized fullerene products.

Methanofullerene Phenyl-C61-Butyric-Acid-Methyl-Ester ([60]PCBM) is an effective solution processable n-type organic semiconductor. It can be blended with p-type conjugated polymers to make photovoltaic (PV) cells^3,4 and thin-film organic field effect transistors (OFETs),⁵ and has also shown promise for use in photodectors.⁶ [60]PCBM is soluble in the same organic solvents as excellent p-type semiconductors such as: MDMO-PPV, MEH-PPV and P3HT (Table 1). This simplifies the preparation of blends and solution processing of heterojuction PV cells and OFETs. The high affinity of PCBM results is efficient photo-induced electron transfer from p-type polymers as well as from metal electrodes in biased thin-film OFETs.⁷ Power conversion efficiencies of up to ~4.4% have been reported for bulk heterojunction PV cells made with [60]PCBM.⁸

Table 1: Conduction (LUMO) and valence (HOMO) band energies of p- and n-type organic semiconductors available from Sigma-Aldrich4,5.

Organic Semiconductor	Product No.	LUMO	HOMO	Soluble in:
MDMO-PPV p-type	546461	-2.8eV	-5.0eV	Chloroform Chlorobenzene Dichlorobenzene Toluene
MEH-PPV p-type	541443 (MW 40 – 70 kDa) 541435 (MW 70 – 100 kDa) 536512 (MW 150 – 250 kDa)	-3.2eV	-5.4eV
P3HT p-type	445703 (regioregular) 510823 (regiorandom) 669067 (electronic grade)	-3.3eV	-5.0eV
PCBM n-type	684430	-3.7eV	-6.1eV

The fabrication of thin film organic electronics devices is complex, with slight variations of molecular structures having profound effects on film morphology and charge transport. To help you optimize the performance of your devices, Sigma-Aldrich is pleased to offer a library of PCBMs that includes [60]PCBM analogs based on higher fullerenes (C₇₀ and C₈₄), as well as those derived by chemical alterations of the addend moeiety to vary solubility and electronic properties. Members of the library have shown advantages in different devices and will help you explore and experiment in your research. Different purity grades of [60]PCBM are available for device scale-up, research, and exploratory work. Tables 2 and 3 below provide application, properties and product information to help you select the PCBMs for your applications.

Table 2: Sigma-Aldrich PCBM Library

Product Number	Product Name	Structure	Applications	Add to Cart
684430	Phenyl-C61-Butyric-Acid-Methyl Ester, [60]PCBM, 99% (scale-up grade)		Best-known PCBM compound. Effective n-type semiconductor soluble in organic solvents. Used for solar cells (OPVs), thin-film transistors (OFETs), and photodetectors.6,10-11
684449	Phenyl-C61-Butyric-Acid-Methyl Ester, [60]PCBM, 99.5% (research grade)
684457	Phenyl-C61-Butyric-Acid-Methyl Ester, [60]PCBM, 99.9% (for exploratory work)
684465	Phenyl-C71-Butyric-Acid-Methyl Ester, [70]PCBM, 99%		[70]PCBM has increased optical absorption in the visible region compared to [60PCBM. This can lead to improved light-harvesting in OPVs,12 especially in combination with large bandgap donors like MDMO-PPV (546461)
684473	Phenyl-C85-Butyric-Acid-Methyl Ester, [84]PCBM, 99%		[84]PCBM has the strongest visible absorption and highest electron accepting ability of available PCBMs. Very low LUMO makes [84]PCBM a promising material for OFETs.13
685321	Phenyl-C61-Butyric-Acid-Butyl Ester, PCBB, [60]PCB-C4> 97%		PCBB is slightly more soluble than [60]PCBM, resulting in improved film morphology and higher performing OPV devices deposited from certain organic solvents (THF, p-xylene).14
684481	Phenyl-C61-Butyric-Acid-Octyl Ester, PCBO, [60]PCB-C8 , 99%		Highly soluble PCBM suitable for applications as a general electron acceptor and scavenger in organic solvents and blends.
688215	Thienyl-C61-Butyric-Acid-Methyl Ester, [60]ThCBM, 99%		PCBM derivative optimized for optimal blending with polythiophene p-type semiconductors, such as P3HT (669067).15
684503	Pentadeuterophenyl-C61-Butyric-Acid-Methyl Ester, d5-PCBM, 99%		Isotopically labeled PCBM for spectroscopic (e.g. SIMS) studies of film morphology and diffusion in thin-film organic devices.

Table 3:  Properties of selected PCBMs *

Product	[60]PCBM	[70]PCBM	[84]PCBM	[60]ThCBM
Product Number	684430 684449 684457	684465	684473	688215
First Reduction Potential, E1/2 (V)	-1.078	-1.089	-0.730	-1.08
Solubility (mg/ml)  · toluene  · p-xylene  · chlorobenzene  · chloroform  · o-dichlorobenzene (ODCB)	10  5  25  25  30	20  10  40  30  70		5  5  10  20  20
Molar Extinction Coefficients (mol-1 cm-1) 400 nm 650 nm	4,900  <1,000	19,000  2,000	28,000  4,000

* From Kronholm, D.; Hummelen, J. Material Matters 2007, Vol. 2 No. 3.
 

References:
1. Newman, C. R.; Frisbie, C. D. et al. Chem. Mater. 16, 4436 (2004).
2. Functionalized Fullerene Materials: Prato, M. and Martin, N. (Eds.) J. Mater. Chem. 12, 1931 (2002).
3. Coakley, K. M.; McGehee, M. D. Chem. Mater. 16, 4533 (2004).
4. Thompson, B. C.; Kim, Y.; Reynolds, J. R. Macomolecules 38, 5359 (2005).
5. Meijer, E. J.; De Leeuw, D. M. et al. Nat. Mater. 2, 678 (2003).
6. Rauch, T.; Henseler, D.; Schilinky, P.; Waldauf, C.; Hauch, J.; Brabec, C. Proc. of the 4th IEEE Conf. on Nanotechnology 632 (2004).
7. Antopoulos, T. D.; Tanase, C. et al. Adv. Mater. 16, 2174 (2004).
8. Li, G.; Shrotriya, V. et al. Nat. Mater. 4, 864 (2005).
9. Gunes, S.; Neugebauer, H.; Sacriciftci, N. Chem. Rev. 107, 1324 (2007).
10. Rauch, T.; Henseler, D.; Schilinky, P.; Waldauf, C.; Hauch, J.; Brabec, C. Proc. of the 4th IEEE Conf. on Nanotechnology 632 (2004).
11. Anthopoulous, T.; de Leeuw, D.; Cantatore, E.; van’t Hof, P.; Alma, J.; Hummelen, J.C. J. Appl.Phys. 98, 503 (2005).
12. Wienk, M.; Kroon, J.; Verhees, W.; Knol, J.; Hummelen, J.; van Hal, P.; Janssen, A. Angew. Chem. Int. Ed. 42, 3371 (2003).
13. Anthopoulous, T.; Kooistra, F.; Wondergem, H.; Kronholm, D.; Hummelen, J.; de Leeuw, D. Adv. Materials 18, 1679 (2006).
14. Zheng, L.; Zhou, Q.; Deng, X.; Yuan, M.; Yu, G.; Cao, Y. J. Phys. Chem. B 108, 11921 (2004).
15. Popescu, M.; van’t Hof, P.; Sieval, A.; Jonkman, H.; Hummelen, J. Appl. Phys. Lett. 89, 213507 (2006).