Investigation of pulsed D.C magnetron sputtering for the component layers of CuInSe2 baseed solar cells

Transcription

1 Investigation of pulsed D.C magnetron sputtering for the component layers of CuInSe2 baseed solar cells Karthikeyan, Sreejith, Hill, AE and Pilkington, RD Title Authors Type URL Published Date 2011 Investigation of pulsed D.C magnetron sputtering for the component layers of CuInSe2 baseed solar cells Karthikeyan, Sreejith, Hill, AE and Pilkington, RD Conference or Workshop Item This version is available at: USIR is a digital collection of the research output of the University of Salford. Where copyright permits, full text material held in the repository is made freely available online and can be read, downloaded and copied for non commercial private study or research purposes. Please check the manuscript for any further copyright restrictions. For more information, including our policy and submission procedure, please contact the Repository Team at: usir@salford.ac.uk.

2 CMMP 11 Investigation of pulsed D.C magnetron sputtering for the component layers of CuInSe 2 based solar cells Sreejith Karthikeyan, Arthur Hill and Richard Pilkington Materials and Physics Research Centre University of Salford, UK

3 Introduction CIS/CIGS thin film based solar cells are the most promising renewable energy source because of their relatively high solar efficiency and stability. Single crystal Si cells need more material to absorb light due to its indirect band gap. In CIS the defect mechanisms makes it a direct semiconducting materials and no doping is needed. Presently CIGS cells have achieved a maximum efficiency of 20.3% [1]. A typical cell CIS/CIGS structure is in the form of a heterojunction. Al-ZnO ~ 1?m 1µm i-zno ~ 70nm CdS ~ 50nm CuInSe 2 ~ 2 1.0? ~ 2µm m Mo layer ~ 0.8? µmm Transparent Conductive Oxide layer Intrinsic ZnO layer to reduce leakage current N- type buffer layer P- type absorber layer Back Contact Substrate References A typical CIGS solar cell [1] P. Jackson et. al Progress in Photovoltaics: Research and Applications, (2011) EU PVSEC WCPEC-5, Valencia, Spain,

4 Introduction The first published report of a CuInSe 2 thin film was by the R.D Tomlinson group at the University of Salford in 1974 [2]. Films of CIS are generally made by multi-step processes My work has been focussed on a SINGLE STEP process which can deposit films with. Nearly stoichiometric ratio. p-type characteristics. No secondary phases. No additional substrate heating for crystallisation. Less material wastage. No carbon, oxygen, chlorine etc. contamination. This work reports such a single step deposition process for nearly stoichiometric p-type CIS layers and also for the other component layers of a cell using Pulsed D.C Magnetron Sputtering (PDMS) from powder targets. References [2] E. Elliott, R.D. Tomlinson, J. Parkes, M.J. Hampshire, Thin Solid Films, 20 (1974) S25-S26. 2

5 Materials Deposited 1. Molybdenum (back contact) 2. Copper indium diselenide (absorber layer) 3. Indium sulphide (buffer layer) 4. Indium oxide (Transparent Conductive Oxide layer) 3

6 Sputtered in argon atmosphere from commercial Mo powder. Films sputtered at different substrate temperatures Molybdenum Films 4

7 XRD of Mo Films Intensit ty (arb.unit) (110) Molp C Molp C Molp203 Molp202 Molp201 Molp C C C 47 0 C θ (degrees) Reference Deposition Parameters Pressure : 7.0x10-3 mbar Mode : Constant Power (50W) Frequency : 75 khz Pulse off Time : 0.5 µs Distance : 10 cm Body-centred cubic phase With increase in substrate temperature A shift in 2θ towards higher angles was noticed. S. Karthikeyan et al, Nano-structured features of pulsed d.c magnetron sputtered Mo films for photovoltaic application Thin Solid Films, 2011, accepted for publication. 5

8 Strain Analysis of Mo Films θ Strai n % Temperature Strain % reduced with increase in temperature 6

9 Resistivity Analysis of Mo Films 2.2x Resistivity 2.0x10 1.8x x10-3 ivity (Ω cm) Resisti 1.4x x x x x x10 4.0x x Temperature ( 0 C) Resistivity reduced with increase in temperature 7

10 SEM and AFM Studies of Mo Films SEM AFM No heating 200 nm C 400 nm Morphological change from a cluster of small grains to a fibrous, columnar needle-likelike structure for films grown at C 200 nm 400 nm References Al-Thani, H.A et al, 2002,Twenty-Ninth IEEE Photovoltaic Specialist Conference, pp

11 Sputtered in argon atmosphere from our CuInSe 2 powder. Films sputtered ed from CIS powder with different compositions Copper Indium Diselenide Films 9

12 CuInSe 2 Crystal Growth Selenium, Indium and Copper inside quartz tube before sealing CuInSe 2 inside ampoule after direct fusion CuInSe 2 polycrystalline ingots CuInSe 2 powder References S.Karthikeyan et al, Thin Solid Films, 2011, 519; pp

13 XRD of CuInSe 2 Films Intens sity (arb. unit) CIST116 CIST115 CIST114 CIST113 CIST111 CIST112 CIST105 CIST104 12) (1 (220/204) (301) (116/312) 5 % extra In (20.53:27.97:51.50) 5 % extra Se (21.54:24.29:54.17) Nearly stoichiometric powder (23.03:23.32:53.66) In rich powder (19.95 : : ) Deposition Parameters Pressure : 7.5x10-3 mbar Mode : Constant Current (0.12A Frequency : 130 khz Pulse off Time : 1.0 µs Distance : 10 cm Preferred (112) orientation Single Phase No heating!! θ Reference S.Karthikeyan et al, Thin Solid Films, 2011, 519; pp

14 Ternary Diagram of CuInSe 2 Films and Powder Stoichiometric Point 45 Film Composition Starting Powder Composition Se % In % Se % Cu % 27.5 In % 55.0 Ternary Diagram All films were p-type References S.Karthikeyan et al, Thin Solid Films, 2011, 519; pp Cu % 12

15 Optical Studies of CuInSe 2 Films Transmitt tance / Refelc ctrance Transmittance Reflectance (1 R) ((1 R ) α =.ln + + R 2 d 2. T 4. T (αhν) E+013 CIS 3Hr ev 8.00E E E E E Wavelength (nm) hν Band gap is very close to the reported value of 1.02 ev 13

16 Sputtered in argon atmosphere from commercial In 2 S 3 powder. Films sputtered at different substrate temperatures Indium Sulphide Films 14

17 XRD of In 2 S 3 Films Deposition Parameters (103) (116) (109) (206) (0 0 12) (1 0 15) (2 2 12) C Pressure : 7.3x10-3 mbar Mode : Constant Power (25 W) Frequency : 100 khz Pulse off Time : 0.5 µs Distance : 8 cm Intensit ty (arb.u) C C C No Heating θ (degrees) Preferred (109) orientation Tetragonal β In 2 S 3 formed with No heating!! 15

18 Optical and AFM studies of In 2 S 3 Films No heating C Band gap decreased with decrease in sulphur content Transm mittance No heating C C C C 200 nm 200 nm Wavelength (nm) 200 nm 200 n Deposition % In %S [% S] Band Gap Temperature [% In] ev Non heated C C C C C 16

19 Reactive sputtered in oxygen and argon atmosphere from commercial In 2 O 3 powder. Films sputtered at different oxygen flow rates with no additional heating Indium Oxide Films 17

20 In 2 O 3 Films X-ray diffraction spectra (211) (222) (400) (440) θ (deg) % 2.5 % 5% 10 % unit) In ntensity (arb. Deposition Parameters Pressure : 4.0x10-3 Pa Mode : Constant Power (60W) Frequency : 60 khz Pulse off Time : 0.5 µs Distance : 9 cm MFC : F Ar + F Oxygen = 20sccm Thickness ~ 500 nm Cubic bixbyite In 2 O 3 phase. Preferred (400) (440) orientation at higher O 2 concentration 18

21 Resistivity of In 2 O 3 Films 5 4 Resistivity 5.09 Ω cm Resis stivity (Ω cm) Strongly n-type 0-2.5% O 2 Weakly n-type 5 10% O Ω cm Ω cm % of O 2 in gas flow 19

22 Optical Properties of In 2 O 3 Films 100 Transm mittance (%) ) (αhν) 2 (m -2.eV 2 ) 1.75E E E E E E E % oxygen flow 3.72 ev 0.00E hν (ev) 3.64 ev 3.67 ev 3.70 ev 3.72 ev O 2 flow 0 % 2.5 % 5.0 % 10 % Wavelength (nm) 20

23 AFM of In 2 O 3 Films 0% O nm 2. Ra 2.63nm 2.5% O nm 2 Ra 3.06nm 200nm 200nm 0.00 nm 5.0% O nm 2 Ra 3.60 nm 10.0% O 2 Ra 4.64 nm nm 0.00 nm 200nm 200nm References Y.C Liang et al, Appl Phys A, 2009, 97; pp nm 0.00 nm 21

24 Conclusion The possibilities of pulsed d.c magnetron sputtering for the deposition of Mo, CuInSe 2 In 2 S 3 and In 2 O 3 films from powdered targets were studied. The analysis showed that these PDMS grown films can be used for solar cell applications. The most surprising outcome is the nearly stoichometric nature of the CIS films largely irrespective of the starting composition of the material Single phase CIS and In 2 S 3 films were produced using PDMS technique without the aid of additional substrate heating. Films grown from this single step process can cut down the cost and also the dangerous selenisation i processes that have previously been associated with the production of high efficiency CIS solar cells. 22

25 Acknowledgements Prof. D.M. Bagnall, School of Electronics and Computer Science, University of Southampton. Prof. P.J. Kelly, Manchester Metropolitan University. Dr. J. Hisek, Technische Universität Braunschweig, Hannover, Germany Dr. H. Yates, Materials and Physics Research Centre, University of Salford Dr. J.S. Cowpe, Materials and Physics Research Centre, University of Salford Mr. G. Parr, Salford Analytical Services, University of Salford. Mr. J. Smith, Physics Technician, University of Salford. Mr. M. Clegg, Physics Technician, University of Salford. Finally, thanks to everybody who has indirectly helped to bring this work to fruition. THANK FOR YOUR ATTENTION Questions? s.karthikeyan@edu.salford.ac.uk 23

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27 Pulsed D.C. Magnetron Sputtering System 100 Pulse off T (μs) K-type Thermocouple Substrate (Anode) Voltage (V) Camera -400 Window N S N S/S * Cover Cu -Target Holder Magnets Water Channel MFC 100 sccm Argon -500 Pulse on Ideal pulsed d.c signal for 100kHz PTFE Insulator S/S * Base Ni-Al Substrate Heater Ni-Cr Water cooling + - AE Pinnacle Plus Power Supply Turbo & Rotary pump Reference S. Karthikeyan et al, Vacuum, 2010, 85; pp Mo powder target 4

28 SEM and AFM CuInSe2 Films ~ nm particle size From stoichiometric powder 500 nm Ra 4.42 nm From 5% extra Se powder 500 nm From 5% extra In powder 500 nm Ra 7.83 nm Ra 7.63 nm 1 7