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Optical Materials Express

Optical Materials Express

  • Editor: David J. Hagan
  • Vol. 3, Iss. 11 — Nov. 1, 2013
  • pp: 1925–1930
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Layer separation driven by laser-induced strain in semiconductor thin film

Stefano Buratin and Paolo Villoresi  »View Author Affiliations


Optical Materials Express, Vol. 3, Issue 11, pp. 1925-1930 (2013)
http://dx.doi.org/10.1364/OME.3.001925


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Abstract

The scribing of the semiconductor layer in thin-film solar cells is here achieved by means of laser induced thermal gradient and mechanical strain. We experimentally demonstrate the scribing by separating one layer from a underlying layer without a substantial melting phase. The modeling of the process was used to predict the spatio-temporal distribution of the induced effects, the resulting scribed channel is confined and the process has a good repeatability. We envisage a parallelization of the process for simultaneous cell formation on the panel.

© 2013 OSA

1. Introduction

The CIGS solar cell represents an exciting approach to address the cost issue in solar devices with relatively moderate efficiency. The current high value for solar conversion efficiency devices had been reported by using multi-junction tandem cell approach in III-V semiconductors [1

1. S. Kurtz and J. Geisz, “Multijunction solar cells for conversion of concentrated sunlight to electricity,” Opt. Express 18, A73–A78 (2010). [CrossRef] [PubMed]

, 2

2. J. F. Geisz, D. J. Friedman, J. S. Ward, A. Duda, W. J. Olavarria, T. E. Moriarty, J. T. Kiehl, M. J. Romero, A. G. Norman, and K. M. Jones, “40.8% efficient inverted triple-junction solar cell with two independently metamorphic junctions,” Appl. Phys. Lett. 93, 123505 (2008). [CrossRef]

]. Recent progress on GaInNAs-containing quantum wells active regions grown on GaAs template had resulted in superior device characteristics [3

3. N. Tansu, J.-Y. Yeh, and L. J. Mawst, “Physics and characteristics of high performance 1200 nm ingaas and 1300–1400 nm ingaasn quantum well lasers obtained by metal–organic chemical vapour deposition,” J. Phys.: Condens. Matter 16, S3277 (2004). [CrossRef]

, 4

4. S. Bank, L. Goddard, M. A. Wistey, H. B. Yuen, and J. S. Harris, “On the temperature sensitivity of 1.5- mu;m gainnassb lasers,” IEEE J. Sel. Top. Quant. Electron. 11, 1089–1098 (2005). [CrossRef]

], which has led to its implementation in four-junction solar cells with 43.5% solar conversion efficiency [5

5. M. Wiemer, V. Sabnis, and H. Yuen, “43.5% efficient lattice matched solar cells,” High and Low Concentrator Systems for Solar Electric Applications VI pp. 810804–810804–5 (2011). [CrossRef]

].

To enhance the efficiency, the processes used in production are asked to provide ultimate performances in terms of control of the action and absence of side effects. Among these processes, the thin films scribing plays a critical role in multilayer solar cells patterning. In the PV modules based on this thin film technology, lasers are able to scribe the metal back contact isolating pattern, a process known as P1, or to eliminate cleanly the semiconductor absorbing layer (P2) or to ablate the front contact isolation (P3) patterns. A relevant example, which will be addressed in the present work is the CIGS cell, in which the P2 process is required to ablate the CIGS layer without damaging the molybdenum layer beneath. This action is known to be critical for providing a high conversion efficiency.

Several groups have already addressed laser P2 process: using pulses in nanosecond regime from a Nd:YAG laser (both 1064 and 532 nm wavelengths) [6

6. P.-O. Westin, U. Zimmermann, and M. Edoff, “Laser patterning of P2 interconnect via in thin-film CIGS PV modules,” Sol. Energ. Mat. Sol. Cells 92, 1230–1235 (2008). [CrossRef]

8

8. P.-O. Westin, U. Zimmermann, M. Ruth, and M. Edoff, “Next generation interconnective laser patterning of CIGS thin film modules,” Sol. Energ. Mat. Sol. Cells 95, 1062–1068 (2011). [CrossRef]

] a Cu vapor (511/578 nm), an XeCl excimer (308 nm), and a KrF excimer (248nm) [9

9. A. Compaan, I. Matulionis, and S. Nakade, “Laser scribing of polycrystalline thin films,” Opt. and Lasers Eng. 34, 15–45 (2000). [CrossRef]

, 10

10. J. Bovatsek, A. Tamhankar, R. Patel, N. Bulgakova, and J. Bonse, “Thin film removal mechanisms in ns-laser processing of photovoltaic materials,” Thin Solid Film 518, 2897–2904 (2010). [CrossRef]

], in ultrafast regime with a Ti:sapphire laser at 800 nm, using a Nd:YVO4 picosecond laser system at 1064 nm [11

11. D. Ruthe, K. Zimmer, and T. Höche, “Etching of CuInSe2 thin films-comparison of femtosecond and picosecond laser ablation,” Appl. Surf. Sci. 247, 447–452 (2005). [CrossRef]

13

13. F. Kessler and D. Rudmann, “Technological aspects of flexible CIGS solar cells and modules,” Sol. Energy 77, 685–695 (2004).Thin Film PV. [CrossRef]

]. These works demonstrated that laser scribing provides processing advantages, but it introduces undesired effects, which are not present in mechanical scribing. Indeed, melting of CIGS at the edges of the grooves could cause short-circuiting and shunting of cells was reported [14

14. A. Wehrmann, S. Puttnins, L. Hartmann, M. Ehrhardt, P. Lorenz, and K. Zimmer, “Analysis of laser scribes at CIGS thin-film solar cells by localized electrical and optical measurements,” Opt. Laser Technol. 44, 1753–1757 (2012). [CrossRef]

]. Moreover, cracks in the molybdenum layer or partial removing of the semiconductor layer can increase the interconnect resistivity [11

11. D. Ruthe, K. Zimmer, and T. Höche, “Etching of CuInSe2 thin films-comparison of femtosecond and picosecond laser ablation,” Appl. Surf. Sci. 247, 447–452 (2005). [CrossRef]

] and a large heat affected zone (HAZ) can increase the shunt resistance [15

15. Y. Hernandez, E. Lotter, V. Bermudez, A. Bosio, F. Salin, M. Hueske, S. Selleri, A. Bertrand, and C. Duterte, “Investigation of CIS/CIGS and CdTe solar cells scribing with high-power fibre short pulse lasers,” Proc. SPIE 8438, Photonics for Solar Energy Systems IV pp. 84380U–84380U–11 (2012). [CrossRef]

].

The minimization of the mechanical stress induced on the underlying molybdenum layer and the thermal damage to the rims of the remaining CIGS layer is also addressed. By using a suitable laser wavelength, power and pulse duration, to match transiently a strong absorption in the semiconductor layer, we obtain the mechanical stress of the CIGS layer that eventually results in its ejection without melting. This approach is attractive because the low power involved is insufficient to melt the layer and the controlled strain gives the opportunity to avoid cracks, burrs and residues that can affect the total efficiency of the panel. The thermal exchange is very limited, so that the HAZ is very restricted and similar to the best cases obtained with ultrafast ablation. The LISA approach could be extended to the other type of layer and is also suitable for parallelization due to the low cost source used.

2. Laser induced thermal gradient and strain in CIGS

In this work, we have considered the cell structure as follows: a glass substrate of 2 mm, a 500 nm molybdenum film, a 2 μm CIGS film and, in the case of process P3 only, a 50nm TCO film [17

17. A. Luque and S. Hegedus, Handbook of Photovoltaic Science and Engineering (Wiley, 2003), chap. 13. [CrossRef]

]. LISA aims are the separation of a selected stripe of CIGS layer from the molybdenum one and that of TCO for P3, without inducing the phase change in to the CIGS. This separation is obtained by exploiting the induced thermal gradient that causes the material expansion. The volume expansion creates strains and induces detachment when the strains reach certain threshold.

The LISA model is present here and also to gain insight on the assessment of the robustness, in term of the variation of the parameters that are effective in LISA.

In accordance with the Lambert-Beer law the energy absorbed from an incident beam of intensity I(z) in material is described in terms of the attenuation of the incident intensity along the propagation direction z, I((z)=λ4πkI(z)z, where λ is wavelength and k is imaginary part of refractive index [18

18. E. D. Palik, Handbook of Optical Constants of Solids (Elsevier, 1998).

].

The energy distribution is analyzed using Fourier equations, without phase transition. This latter condition has been verified numerically from the model. The thermal distribution is then as follows [19

19. F. Incropera and D. DeWitt, Fundamentals of Heat and Mass Transfer (John Wiley and Sons, 1996), 4th ed.

21

21. Ramon and Codina, “Comparison of some finite element methods for solving the diffusion-convection-reaction equation,” Comput.Methods in Appl.Mech.Eng. 156, 185–210 (1998). [CrossRef]

]:
λTT+S=ρCpTt,
(1)
where: ρ is density; Cp is specific heat; λT is thermal conductivity and T temperature in (x, y, z) at the time t. The heat is provided by the source term, S(x,y,z,t)=I(z)e(xx0)6e(yy0)6e(t4ττ)2 which is laser flux in (x, y, z) at time t; x0 = 5μm, y0 = 100μm, τ = 0.5μs.

The boundary conditions for the thermal flux have only one non-adiabatic face, in which the laser impinges: nz · (kT)|surface = S(0)|surface. For all the other faces the condition is then n· (kT) = 0, with gradient n indicating the lateral and bottom faces. The initial temperature is set to 293 K.

The strain conditions are defined by the deformation components u, v, and w and their derivatives. The precise relation between strain and deformation depends on the relative magnitude of the displacement [22

22. L. D. Landau and E. M. Lifsits, Theory of Elasticity (Pergamon Press, 1986).

]. The strain in the layer is only caused by thermal gradient, (εth), with its initial ε0 = 0.

From the solution of Eq.(1) we calculated the relevant thermal strain components using εijth=αij(TTref), where αij are the thermal expansion coefficients, which is in our case symmetric.

The stress-strain relationship is the final step, and it reads [23

23. W. S. Slaughter, The Linearized Theory of Elasticity (Birkhauser, 2002). [CrossRef]

]
σ=Dεth,
(2)
where σ and D are the stress and elasticity tensors for isotropic materials [24

24. M. A. Slawinski, Waves and Rays in Elastic Continua (World Scientific Publishing Co. Pte. Ltd., 2010), 2nd ed. [CrossRef]

]
D=[λL+2μLλLλL000λLλL+2μLλL000λLλLλL+2μL000000μL000000μL000000μL]

The quantities λL and μL are the Lamè’s first and second parameters, they are strongly dependent on the type of material and its deposition technique.

The boundary conditions imposed for the mechanical strain depends on the structure, and permits to decide if they are fixed or if it is free to move in one or more directions. In the model only the top face is free. For the remaining surfaces u=0, because there is no displacement.

3. FEM results

Figure 1 shows the temporal evolution of temperature in the center of the laser spot, in different points inside the target. The target, or almost the volume of the film, didn’t exceed the melting temperature (1600 K). On the bottom face, the temperature reached was lower, thus far below the melting temperature of molybdenum (2896 K). From the figure we may verify that the temperature of about 500 K reached inside the film, results significantly lower than the melting point.

Fig. 1 Temperature distribution along z axis in the center of the spot and pulse shape (black) x0=100 μm, y0=5 μm, τ =0.5μs, λ =808 nm; k=0.27 silica glass ρ =2203 Kg/cm3, Cp=703J/(Kg °K), λT =1.38 W/m°K CIGS ρ =5770 Kg/cm3,Cp=300J/(Kg°K), λT =3.7W/m°K molybdenum ρ =10200 Kg/cm3, Cp=255J/(Kg °K), λT =138W/m °K [25][17][26][18]The legend shows different line types for different point in z axis from 0.2 to 1.8 μm

Figure 2 shows the value of first principal stress, from which we may see that it is increasing toward the lower film interface. The peak value reaches several tens of MPa. In Fig. 3 is plotted the second principal stress (the third was symmetric for the geometry of the laser spot). Here the peak value was larger, of about several hundreds of MPa. As this effect induces a strain orthogonal to the layer larger than the adhesion force of the CIGS/Mo interface, it would result in the detachment of the irradiated layer.

Fig. 2 First principal stress with the detachment threshold [27] and its directions silica glass α = 0.55e − 6[1/°K] E = 73.1GPa, ν = 0.17 CIGS α = 8e − 6[1/°K] E = 50GPa, ν = 0.4 molybdenum α = 4.8e − 6[1/°K] E = 312GPa, ν = 0.3 The legend shown different types of line for different point in z axis from 0.2 to 1.8 μm
Fig. 3 Second principal stress and directions of second and third principal stress The legend shown different line types for different point in z axis from 0.2 to 1.8 μm

Typically the yield strength of a single crystal CIS (about 0.91 GPa [28

28. Landolt-Börnstein, Group III Condensed Matter Numerical Data and Functional Relationships in Science and Technology (Springer, 2000), vol. 41E, chap. Copper indium selenide (CuInSe2) thermal expansion, Debye temperature, melting point and other lattice parameters.

]) is higher than the adhesion threshold and we can’t assume it as threshold. At the same time not exceeding the yield strength of the crystal is important to avoid cracks out of the channel. In practice, the adhesion force depends on several parameters of the deposition method. However, we can analyse some adhesion tests used to measure peel resistance for CIGS. From these tests the strength of adhesion of CIGS/MO is one of the lower compared with many others kinds of solar films [27

27. T. J. McMahon and G. J. Jorgensen, “Adhesion and thin-film module reliability,” Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference on2, 2062–2065 (7–12 May 2006).

]. It is clear that CIGS/MO patterning by induced stress is a good solution. Unfortunately peel test physical implications are quite different to LISA physical implications and it couldn’t be compared directly, but it is relevant to know the characteristic of the interface compared with other solar cells type.

4. Experimental results

LISA was realized with a pulsed laser diode with a high current capacity driver at 1 kHz. The average power varied from 1 to 10 mW. The wavelength (808 nm) was chosen in order to obtain strong absorption. A precise translation stage was used to scan the cell under the laser focus. In Fig. 4 are shown some frames from the video taken during LISA ablation that clarify the process: the light grey channel is the underlying molybdenum layer, the black part is the CIGS layer. In particular in this image there are 2 important phenomena: the lifting of the CIGS and its detachment in rectangular solid fragments of the size of the laser focus.

Fig. 4 Images of the LISA process on CIGS, channel width 180 μm. From left to right there are 3 different frames captured during the process, in the first and in the second there is a partial lift off and in the third a fragment is detached

The experimental results of laser scribing are analyzed with a scanning electron microscope (SEM). Figure 5(a) shows a relevant example, from which we may draw the following observations: 1) the irradiated area is clear from CIGS residuals; 2) the removal left clean rims of the CIGS edges, with only sporadic deformation; 3) no cracks are induced in the remaining CIGS layer. Figure 5(b) (4000× magnification) shows an example of residual defects at the channel rim in the case where only some tens nanometers are melted. In this case the defect spans a small fraction of the channel width, that was set to 180 μm. There isn’t slope on the edges and the shape of the channel is clean and vertical, also nearby the defect. This means that there isn’t a region where the pulse energy shape affects the layer as opposed to the classical scribing with gaussian pulse. There isn’t debris near the edge as well as in the center of the channel Fig. 5(a). Using low thermal gradient we can reach the total absence of micro cracks because the area interested by the cracks is only the removed area. The HAZ is limited only to some micrometers from the channel because a low peak power was used for inducing stress.

Fig. 5 SEM images of the channel. Scale bars are 100 and 10 μm respectively on the left and on the right.

5. Conclusion

To sum up, LISA appears to be an effective method for the removal of an adsorbing layer such as CIGS on molybdenum. The very low power used prevents the induction of permanent damages and the melting of the layer. The induced stresses are localized in the channel and without any cracks out of it. These latter advantages are crucial for preserving the efficiency of the cell. The experimental results were confirmed by a numerical calculation, thus fostering its introduction as an effective process for the solar technology.

Acknowledgments

This work has been carried out at the Laser4PV Labs of Polo Fotovoltaico, University of Padova. We gladly acknowledge the financial support of Contract CNR IMEM n. 373/2009. We wish to thank Dr. M. Mazzer and Dr. S. Rampino of CNR IMEM, Parma - Italy, for the helpful discussions and for providing the CIGS samples.

References and links

1.

S. Kurtz and J. Geisz, “Multijunction solar cells for conversion of concentrated sunlight to electricity,” Opt. Express 18, A73–A78 (2010). [CrossRef] [PubMed]

2.

J. F. Geisz, D. J. Friedman, J. S. Ward, A. Duda, W. J. Olavarria, T. E. Moriarty, J. T. Kiehl, M. J. Romero, A. G. Norman, and K. M. Jones, “40.8% efficient inverted triple-junction solar cell with two independently metamorphic junctions,” Appl. Phys. Lett. 93, 123505 (2008). [CrossRef]

3.

N. Tansu, J.-Y. Yeh, and L. J. Mawst, “Physics and characteristics of high performance 1200 nm ingaas and 1300–1400 nm ingaasn quantum well lasers obtained by metal–organic chemical vapour deposition,” J. Phys.: Condens. Matter 16, S3277 (2004). [CrossRef]

4.

S. Bank, L. Goddard, M. A. Wistey, H. B. Yuen, and J. S. Harris, “On the temperature sensitivity of 1.5- mu;m gainnassb lasers,” IEEE J. Sel. Top. Quant. Electron. 11, 1089–1098 (2005). [CrossRef]

5.

M. Wiemer, V. Sabnis, and H. Yuen, “43.5% efficient lattice matched solar cells,” High and Low Concentrator Systems for Solar Electric Applications VI pp. 810804–810804–5 (2011). [CrossRef]

6.

P.-O. Westin, U. Zimmermann, and M. Edoff, “Laser patterning of P2 interconnect via in thin-film CIGS PV modules,” Sol. Energ. Mat. Sol. Cells 92, 1230–1235 (2008). [CrossRef]

7.

P.-O. Westin, S. Schmidtb, and M. E. M. Huskeb, “Influence of spacial and temporal laser beam characteristics on thin-film ablation,” 24th European Photovoltaic Solar Energy Conference, 2009, Germany.

8.

P.-O. Westin, U. Zimmermann, M. Ruth, and M. Edoff, “Next generation interconnective laser patterning of CIGS thin film modules,” Sol. Energ. Mat. Sol. Cells 95, 1062–1068 (2011). [CrossRef]

9.

A. Compaan, I. Matulionis, and S. Nakade, “Laser scribing of polycrystalline thin films,” Opt. and Lasers Eng. 34, 15–45 (2000). [CrossRef]

10.

J. Bovatsek, A. Tamhankar, R. Patel, N. Bulgakova, and J. Bonse, “Thin film removal mechanisms in ns-laser processing of photovoltaic materials,” Thin Solid Film 518, 2897–2904 (2010). [CrossRef]

11.

D. Ruthe, K. Zimmer, and T. Höche, “Etching of CuInSe2 thin films-comparison of femtosecond and picosecond laser ablation,” Appl. Surf. Sci. 247, 447–452 (2005). [CrossRef]

12.

J. Hermann, M. Benfarah, G. Coustillier, S. Bruneau, E. Axente, J.-F. Guillemoles, M. Sentis, P. Alloncle, and T. Itina, “Selective ablation of thin films with short and ultrashort laser pulses,” Appl. Surf. Sci. 252, 4814–4818 (2006). [CrossRef]

13.

F. Kessler and D. Rudmann, “Technological aspects of flexible CIGS solar cells and modules,” Sol. Energy 77, 685–695 (2004).Thin Film PV. [CrossRef]

14.

A. Wehrmann, S. Puttnins, L. Hartmann, M. Ehrhardt, P. Lorenz, and K. Zimmer, “Analysis of laser scribes at CIGS thin-film solar cells by localized electrical and optical measurements,” Opt. Laser Technol. 44, 1753–1757 (2012). [CrossRef]

15.

Y. Hernandez, E. Lotter, V. Bermudez, A. Bosio, F. Salin, M. Hueske, S. Selleri, A. Bertrand, and C. Duterte, “Investigation of CIS/CIGS and CdTe solar cells scribing with high-power fibre short pulse lasers,” Proc. SPIE 8438, Photonics for Solar Energy Systems IV pp. 84380U–84380U–11 (2012). [CrossRef]

16.

P. Villoresi and S. Buratin, “Laser scribing process, PCT/EP2011/064287,” (2011).

17.

A. Luque and S. Hegedus, Handbook of Photovoltaic Science and Engineering (Wiley, 2003), chap. 13. [CrossRef]

18.

E. D. Palik, Handbook of Optical Constants of Solids (Elsevier, 1998).

19.

F. Incropera and D. DeWitt, Fundamentals of Heat and Mass Transfer (John Wiley and Sons, 1996), 4th ed.

20.

A. Bejan, Heat Transfer (Wiley, 1993).

21.

Ramon and Codina, “Comparison of some finite element methods for solving the diffusion-convection-reaction equation,” Comput.Methods in Appl.Mech.Eng. 156, 185–210 (1998). [CrossRef]

22.

L. D. Landau and E. M. Lifsits, Theory of Elasticity (Pergamon Press, 1986).

23.

W. S. Slaughter, The Linearized Theory of Elasticity (Birkhauser, 2002). [CrossRef]

24.

M. A. Slawinski, Waves and Rays in Elastic Continua (World Scientific Publishing Co. Pte. Ltd., 2010), 2nd ed. [CrossRef]

25.

D. R. Lide and C. R. Company, CRC Handbook of Chemistry and Physics (CRC Press, 1998).

26.

A. F. Wells, Structural Inorganic Chemistry (Clarendon Press, 1990), 5th ed.

27.

T. J. McMahon and G. J. Jorgensen, “Adhesion and thin-film module reliability,” Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference on2, 2062–2065 (7–12 May 2006).

28.

Landolt-Börnstein, Group III Condensed Matter Numerical Data and Functional Relationships in Science and Technology (Springer, 2000), vol. 41E, chap. Copper indium selenide (CuInSe2) thermal expansion, Debye temperature, melting point and other lattice parameters.

OCIS Codes
(040.5350) Detectors : Photovoltaic
(140.3390) Lasers and laser optics : Laser materials processing
(240.0310) Optics at surfaces : Thin films
(350.6050) Other areas of optics : Solar energy

ToC Category:
Laser Materials Processing

History
Original Manuscript: August 26, 2013
Revised Manuscript: September 2, 2013
Manuscript Accepted: September 2, 2013
Published: October 22, 2013

Citation
Stefano Buratin and Paolo Villoresi, "Layer separation driven by laser-induced strain in semiconductor thin film," Opt. Mater. Express 3, 1925-1930 (2013)
http://www.opticsinfobase.org/ome/abstract.cfm?URI=ome-3-11-1925


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References

  1. S. Kurtz and J. Geisz, “Multijunction solar cells for conversion of concentrated sunlight to electricity,” Opt. Express18, A73–A78 (2010). [CrossRef] [PubMed]
  2. J. F. Geisz, D. J. Friedman, J. S. Ward, A. Duda, W. J. Olavarria, T. E. Moriarty, J. T. Kiehl, M. J. Romero, A. G. Norman, and K. M. Jones, “40.8% efficient inverted triple-junction solar cell with two independently metamorphic junctions,” Appl. Phys. Lett.93, 123505 (2008). [CrossRef]
  3. N. Tansu, J.-Y. Yeh, and L. J. Mawst, “Physics and characteristics of high performance 1200 nm ingaas and 1300–1400 nm ingaasn quantum well lasers obtained by metal–organic chemical vapour deposition,” J. Phys.: Condens. Matter16, S3277 (2004). [CrossRef]
  4. S. Bank, L. Goddard, M. A. Wistey, H. B. Yuen, and J. S. Harris, “On the temperature sensitivity of 1.5- mu;m gainnassb lasers,” IEEE J. Sel. Top. Quant. Electron.11, 1089–1098 (2005). [CrossRef]
  5. M. Wiemer, V. Sabnis, and H. Yuen, “43.5% efficient lattice matched solar cells,” High and Low Concentrator Systems for Solar Electric Applications VI pp. 810804–810804–5 (2011). [CrossRef]
  6. P.-O. Westin, U. Zimmermann, and M. Edoff, “Laser patterning of P2 interconnect via in thin-film CIGS PV modules,” Sol. Energ. Mat. Sol. Cells92, 1230–1235 (2008). [CrossRef]
  7. P.-O. Westin, S. Schmidtb, and M. E. M. Huskeb, “Influence of spacial and temporal laser beam characteristics on thin-film ablation,” 24th European Photovoltaic Solar Energy Conference, 2009, Germany.
  8. P.-O. Westin, U. Zimmermann, M. Ruth, and M. Edoff, “Next generation interconnective laser patterning of CIGS thin film modules,” Sol. Energ. Mat. Sol. Cells95, 1062–1068 (2011). [CrossRef]
  9. A. Compaan, I. Matulionis, and S. Nakade, “Laser scribing of polycrystalline thin films,” Opt. and Lasers Eng.34, 15–45 (2000). [CrossRef]
  10. J. Bovatsek, A. Tamhankar, R. Patel, N. Bulgakova, and J. Bonse, “Thin film removal mechanisms in ns-laser processing of photovoltaic materials,” Thin Solid Film518, 2897–2904 (2010). [CrossRef]
  11. D. Ruthe, K. Zimmer, and T. Höche, “Etching of CuInSe2 thin films-comparison of femtosecond and picosecond laser ablation,” Appl. Surf. Sci.247, 447–452 (2005). [CrossRef]
  12. J. Hermann, M. Benfarah, G. Coustillier, S. Bruneau, E. Axente, J.-F. Guillemoles, M. Sentis, P. Alloncle, and T. Itina, “Selective ablation of thin films with short and ultrashort laser pulses,” Appl. Surf. Sci.252, 4814–4818 (2006). [CrossRef]
  13. F. Kessler and D. Rudmann, “Technological aspects of flexible CIGS solar cells and modules,” Sol. Energy77, 685–695 (2004).Thin Film PV. [CrossRef]
  14. A. Wehrmann, S. Puttnins, L. Hartmann, M. Ehrhardt, P. Lorenz, and K. Zimmer, “Analysis of laser scribes at CIGS thin-film solar cells by localized electrical and optical measurements,” Opt. Laser Technol.44, 1753–1757 (2012). [CrossRef]
  15. Y. Hernandez, E. Lotter, V. Bermudez, A. Bosio, F. Salin, M. Hueske, S. Selleri, A. Bertrand, and C. Duterte, “Investigation of CIS/CIGS and CdTe solar cells scribing with high-power fibre short pulse lasers,” Proc. SPIE8438, Photonics for Solar Energy Systems IV pp. 84380U–84380U–11 (2012). [CrossRef]
  16. P. Villoresi and S. Buratin, “Laser scribing process, PCT/EP2011/064287,” (2011).
  17. A. Luque and S. Hegedus, Handbook of Photovoltaic Science and Engineering (Wiley, 2003), chap. 13. [CrossRef]
  18. E. D. Palik, Handbook of Optical Constants of Solids (Elsevier, 1998).
  19. F. Incropera and D. DeWitt, Fundamentals of Heat and Mass Transfer (John Wiley and Sons, 1996), 4th ed.
  20. A. Bejan, Heat Transfer (Wiley, 1993).
  21. Ramon and Codina, “Comparison of some finite element methods for solving the diffusion-convection-reaction equation,” Comput.Methods in Appl.Mech.Eng.156, 185–210 (1998). [CrossRef]
  22. L. D. Landau and E. M. Lifsits, Theory of Elasticity (Pergamon Press, 1986).
  23. W. S. Slaughter, The Linearized Theory of Elasticity (Birkhauser, 2002). [CrossRef]
  24. M. A. Slawinski, Waves and Rays in Elastic Continua (World Scientific Publishing Co. Pte. Ltd., 2010), 2nd ed. [CrossRef]
  25. D. R. Lide and C. R. Company, CRC Handbook of Chemistry and Physics (CRC Press, 1998).
  26. A. F. Wells, Structural Inorganic Chemistry (Clarendon Press, 1990), 5th ed.
  27. T. J. McMahon and G. J. Jorgensen, “Adhesion and thin-film module reliability,” Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference on2, 2062–2065 (7–12 May 2006).
  28. Landolt-Börnstein, Group III Condensed Matter Numerical Data and Functional Relationships in Science and Technology (Springer, 2000), vol. 41E, chap. Copper indium selenide (CuInSe2) thermal expansion, Debye temperature, melting point and other lattice parameters.

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