SAM as improving holes injection of Indium Tin Oxide

Figure 4.8 shows the J-V characteristics of diode with ITO chemically modified with –COCl binding groups of p-chlorobenzene derivatives. In Figure 4.8, J-V

characteristics of hole-only single-layer devices with ITO modified with p-chlorobenzene derivatives with –COCl binding groups are compared with those of the device with as-cleaned ITO. While ITO treated with –COCl gave the intermediate J-V characteristics that are much better than those of as-cleaned ITO. These results suggest that the efficient hole injection into Pentacene. It is because that the increase in the work function of ITO covered with the two dipole layers introduced by the surface modification. Therefore, the device characteristics are strongly correlated with the change in the observed work functions of various modified ITO.

4.5 Discussion

1. The characteristics of Al/SAM/Al and Al/SIO/Al.

Figure 4.9 shows the characteristics of Al/SAM/Al and Al/SIO/Al. When the operating voltage is 1V the leakage with thickness of SIO is 30-nm, the leakage current level is 10^-2 to 10^-3mA/cm². When the operating voltage is 1V the leakage with n-octadecylphosphonic acid, the leakage current level is 10^-3 to 10^-4mA/cm². The result of the insulating properties of n-octadecylphosphonic acid is superior to SIO. It is because that n-octadecylphosphonic acid uses functional groups to attach with alumina on aluminum surface. It can reduce the leakage current from the side of aluminum. Therefore, the benefits of n-octadecylphosphonic acid are fast fabrication, good coverage, and can reach the lower leakage current than SIO.

2. The difference of Au/pentacene/Al and ITO/pentacene/Al

Figure 4.10 shows the diode characteristics of different bottom metal. When the operating voltage is 1V the characteristic of ITO-based diode is better than Au-based diode. For our device operating voltage is no more than 1V, therefore under the condition ITO-based is better than Au-based for Pentacene SCLT.

Chapter 4

(a) (b) (c)

Figure 4.1 Self-assembled monolayer dielectrics (a) Chemical structure of 4-hexadecyloxybenzoic acid. (b) Chemical structure of n-octadecylphosphonic acid.

(C) Chemical structure of p-chlorobenzoyl chloride dichloride.

Figure 4.2 Schematic of energy diagrams for ITO treated/Pentacene/Al hole-only single-carrier devices.

Glass Al Al Glass

Al Al

organic

Glass Al Al organic

Glass Al Al

Figure 4.3 Structure of the diode (Al/SAM/Al) and diode.

Figure 4.4 Structure of the diode (Al/SAM/organic/Al) in this work.

o rg a n ic

G la s s IT O

A l o rg a n ic

G la s s IT O

A l

Figure 4.5 Structure of the diode (ITO/SAM /Al) and the diode in this work.

-4 -2 0 2 4 10

^-4

10

^-3

10

^-2

10

^-1

10

⁰

10

¹

10

²

10

³

10

⁴

Al/Al

Al/SAM 1/Al Al/SAM 2/Al

J( m A /c m

2 )

V(V)

Figure 4.6 The insulator characteristic of different SAM.

-4 -2 0 2 4

-4 -2 0 2 4 10

^-6

10

^-5

10

^-4

10

^-3

10

^-2

10

^-1

10

⁰

10

¹

10

²

V(V)

J( m A /c m

2 )

Al/C60/Al

Al/SAM/C60/Al

(C)

Figure 4.7 The insulator characteristics of Al/SAM/organic/Al diodes. (a) Comparison of Al/P3HT/Al and Al/SAM/P3HT/Al, (b) Comparison of Al/Pentacene/Al and Al/SAM/Pentacene/Al and (c) Comparison of Al/C60/Al and Al/SAM/C60/Al

-2 0 2 4 10

^-7

10

^-5

10

^-3

10

^-1

10

¹

10

³

10

⁵

V(V)

J( m A /c m

2 )

ITO/Pentacene/Al ITO/SAM/Pentacene/Al

-4 -2 0 2 4

10

^-5

10

^-4

10

^-3

V(V)

J( m A /c m

2 )

Al/SIO/Al Al/SAM/Al

Figure 4.8 The J-V characteristics of diode with ITO chemically modified with –COCl binding groups of p-chlorobenzene derivatives

Figure 4.9 shows the characteristics of Al/SAM/Al and Al/SIO/Al.

Figure 4.10 shows the diode characteristics of different bottom metal.

-2 0 2 4 6 8 10

10

^-9

10

^-2

10

⁵

J( m A /c m

2 )

V(V)

Au/Pentacene/Al

ITO/SAM/Pentacene/Al

Chapter 5

Conclusions

We try to fabricate the low operation voltage space-charge-limited transistor (SCLT) with new structure and investigate the effects of self-assembled-monolayer (SAM) on Al or ITO surface. A 1-V P3HT-based SCLT with on/off current ratio 24310 is firstly demonstrated. Significant impacts of thin film morphology on the leakage current of organic SCLTs are firstly observed and recognized as new leakage phenomena. Surface profile reveals that the grain structure in pentacene/C60 produces holes make the top metal penetrates into pentacene/C60 film and shield the base electric field while P3HT have rather smooth and dense morphology. Therefore, pentacene SCLTs and C60 SCLTs suffer from high leakage current even when base leakage is as low as in P3HT SCLTs.

We tried to reduce the production time and increase output current by using SAMs. N-octadecylphosphonic acid using OH groups to attach with alumina on Al surface to reduce the leakage current from the side of Al. Therefore, it is faster fabrication, better coverage, and
lower leakage current than SIO. P-chlorobenzene derivative with –COCl binding groups is used to increase the work function of ITO.

For our device operating voltage is no more than 1V, therefore under the condition ITO-based is better than Au-based for Pentacene SCLT.

In future work, we will try to solve the morphology effect by spin solution-processed polymer on pentacene. We will fabricate SCLTs with various bottom metal based on this thesis results.

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8.35E-6

Table 3.1 Typical parameters of vertical transistors.

在文檔中 導電性高分子聚合物/有機材料及自我組裝單分子層在空間電荷限制電晶體中的應用 (頁 50-0)