Energy Level Analysis of Nano and Organic Semiconductor by Photoelectron Spectroscopy

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1 Energy Level Analysis of Nano and Organic Semiconductor by Photoelectron Spectroscopy T. C. Tien 1 J. L. Chen 1 M. T. Shien 2 C. J. Hwang 2 L. N. Tsai 2 Y. J. Shuin 2 L. J. Lin 1,3 (MCL/ITRI) / / / (Dipole Layer) (Alignment) (UPS) X (XPS) / / / Abstract To study the efficiency of optoelectronics, measuring energy band structure and alignment in device become a more and more importance issues today, especially, at the interface of organic/inorganic, organic/ organic materials, dipole layer might be a key issue to interfere charge transport. Base on above reason, we investigated the most directive method of studying interface band alignment: Ultrat-violet Photoelectron Spectroscopy (UPS), and X-ray Photoelectron Spectroscopy (XPS) was used to study chemical state at interface. Moreover, discussion on relation among band structure, chemical state and interface dipole at recent development were believed to make a contribution to enhance the efficiency of organic device and to develop advance flexible device in the future. /Key Words (Ultrat-violet Photoelectron Spectroscopy; UPS) X (X-ray Photoelectron Spectroscopy; XPS) (Dipole Layer) (Nano and Organic Semiconductor)

2 / Gleiter T. Minemoto et al. XPS CIGS-based Zn 1-x Mg x O/CIGS / Conduction Band Offset (CBO) (1) R. Puthenkovilakam and J. P. Chang XPS Plasmon Loss Spectrum IC Bandgap HfO 2 HfSiO 4 (2) (OLED) / (3) (Band Alignment) Bending (Dipole Layer) (UPS) Kelvin Probe Highest Occupied Molecular Orbital (HOMO) UPS X (XPS) (Shake-up Peak) / Lowest Unoccupied Molecular Orbital (LUMO) UPS/XPS UPS/XPS X-ray or UV 1S 2S 2P...HOMO... (Binding Energy) E(x) = hv Ek-Φ E(x) x x HOMO HOMO hv X-ray r UV Ek Φ (Ek)

3 / HOMO UPS (Φm) = (hν) (Wm) UPS XPS UPS 5eV 5 ev XPS 15eV X-ray 5eV UPS XPS (95%) 5nm (4) UPS HOMO HOMO UPS HOMO (WF) XPS UPS LUMO LUMO LUMO UV K L M (UPS) X-ray X-ray/UV UPS/XPS hv E m vac E m F (XPS) KE W m Φ m Vacuum HOMO LUMO C2 Peak XPS Peak C1 C2 Peak HOMO LUMO HOMO LUMO (Shake-up) (Shake-up Peak) / Ultraviolet and Visible Spectroscopy HOMO/LUMO Polystylene Film (PS) 5~1 nm 2 nm (NP-Au) Sol-gel 2~3 w/o NP-Au/ PS XPS NP-Au PS Film(#PS) NP-Au PS Film (#Au/ PS) NP-Au PS Film 2% Si 5%

4 Sol-gel Solution S 5% (Band Gap) #Au/PS #PS PS Film 6.7 ev PS (#PS) PS Film (#Au/PS) HOMO/LUMO V1 V5 Peak Binding Energy (B.E.) Peak #PS V1 B.E eV PS #Au/PS Sample V1 B.E ev.12 ev 14 Overlay #PS HOMO 2.5 ev 12 #PS V4 V3 1 #Au/PS V2 PS #Au/PS Sample 8 #PS HOMO 2.62 ev NP Au 6 V4 V3 V2 V1 O ev 4 PS #Au/PS 2.5eV 2 Peak Name V1 V2/V2 V3/V3 V4/V4 PS B.E. (ev) / / /24.9 Film(#PS) PS Film (#Au/PS) C1s XPS NP-Au/Polystylene Film Before XPS During XPS LUMO HOMO 2S 1S LUMO HOMO 2S 1S LUMO HOMO 2S 1S Residuals C1: C-C, C-H C2: π Shake-up 6.E+4 C3: Plasmon Peak 5.E+4 4 C3 C2 5 4.E Peak BE Area Ratio C Cls C1 C C E+4 7.E+4 C1 C2 XPS C2 (Shake-up Peak)

5 PS Film (#Au/ PS) S2p XPS Fitting (Sulfate) (Sulfide) 1:5 HOMO/ LUMO 26 Shake-up Peak 24 2 nm 22 2 ZnSe (QDs) N,N-diphenyl-N,N- 18 bis(3-methylphenyl)- (1,1-biphenyl)-4, diamine(tpd) ~1 8 nm ZnSe ~1 nm 5 nm TEM ZnSe Name HOMO Band Gap LUMO TPD (Segregation) #PS PS in #Au/PS 2.6? ? ZnSe NP-Au/Polystylene Film C1s XPS (a) ZnSe QDs TPD (b) ZnSe QD TPD UPS 1.2E+4-2 S2p 1.1E+4 (Valence Band -4-6 Sulfate : Sulfide = 1 : 5 S2pA 1.+4 Maximum; VBM) -8 S2pB 9.E+3-1 Sulfate ZnSe QDs TPD -12 S2pC Sulfide 8.E+3-14 S2pE S2pD 7.E+3 VBM (Benzene) 2p E+3 UPS ZnSe QDs 5.E+3 1 ev (a) 2s UPS ZnSe QDs 2p UPS NP-Au/Polystylene Film S2p XPS Residuals Overlay #PS #Au/PS Cls Peak Shake-up Overlay #PS #Au/PS

6 ZnSe QDs Methyl Benzene ZnSe QDs TPD (21.22 ev-cut Off) ZnSe QDs UPS TPD (a) ZnSe QDs TPD (b) ZnSe QD TPD C1s XPS ZnSe QD TPD 2.39 ev 3.74 ev ZnSe QDs TPD (Conduction Band Minimum; CBM) QDs TPD VBM CBM 1.35 ev (Dipole) (5) (NP- ) Zn-Tin-Oxide () (ALD) 1 nm DSSC DSSC VBM -3.7 ev -4.7eV Intensity (arb. unit.) 12M 8M 4M HeI C2s (Benzene) + Cut off = 17.4 C2p (Benzene)* VBM = (a) (DSSC) 12M HeI C2s (Benzene) + C2p (Benzene)* (a) (b) Intensity (arb. unit.) 8M 4M Cut off = 17.4 VBM = nm 2nm ZnSe (QDs) TPD TEM (b) (a) ZnSe QDs TPD (b) ZnSe QD TPD UPS

7 (a) Intensity (arb. unit) π(2) π(1) Shake up Epeak = π(1) = π(2) = (b) Intensity (arb. unit) π(2) π(1) Shake up Epeak = π(1) = π(2) = ev 1 nm / / Experimental Results of Energy Band Analysis of ZnSe QDs Film Samples QDs Film Non-QDs Film Valence Band Maximum (VBM) ev ev Band-gap 3.74 ev 2.39 ev Conduction Band Minimum (CBM) 2.2 ev.67 ev 1 Experimental Results of Energy Band Analysis of Cathode in DSSC (a) ZnSe QDs TPD (b) ZnSe QD TPD C1s XPS Samples Valence Band Maximum (VBM) ev -4.7 ev Work Function (WF) 3.42 ev 3.36 ev 3.22 ev MDOCUME-1\83439\LOCALS~1\Temp\VGD12C7tmp MDOCUME-1\83439\LOCALS~1\Temp\VGD12C7tmp MDOCUME-1\83439\LOCALS~1\Temp\VGD12C7tmp SE 1 nm NP- WF VBM DSSC

8 ( ) / / / / Ti O 2 Ti O 2 / (Dipole) ( ) Dipole (6) / / / / (UPS) X (XPS) / / / E vac E f 3.42 Z-T = T-A = VBM (DSSC) 1. T. Minemoto et al., Appl. Phys. Lett., Vol. 89, No 12, 8327 (21). 2. R. Puthenkovilakam and J. P. Chang,, J. Appl. Phys., Vol. 96, No 5, 271 (24). 3. P.235 (25) 4. Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy (Edit by D.Briggs and M.P Seah) H. Ishii, K. Sugiyama, E. Ito, and K. Seki, Adv. Mater. 8, 65 (1999)

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