# An Investigation into CIGS Thin-Films Solar Cell P2 Layer Scribing Depth and Width Using Different Laser Process Parameters

Authors: Dyi-Cheng Chen; Ming-Fei Chen; Ming-Ren Chen
Journal: Advances in Materials Science and Engineering
 (2015)

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## Abstract

This study will be about UV (355 nm) laser processing system as a carrier. It studied electrode insulated characteristic using laser direct forming for CIGS solar cell technology P2 layer of stainless steel. It explored the impact of this process on the way to stainless steel substrate P2 film sizes using its laser different focus position, energy density, and scanning velocities. According to the experiment results, the scribing results are straight line and larger width under minus leave perpendicularity and positive leave perpendicularity and the laser scanning velocities at 10~1000 mm/s underline width about 0.96μm~1.07 μm. The experiment results confirm that the laser apparatus is effective when applied to a stainless steel CIGS solar cell P2 layer.


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## Body

## 1. Introduction

The energy is the important elements that the mankind depends on to support the family now. Membrane processes have the important role which raised the efficiency and lowered costs of solar cell material using laser process. The fabrication of the P2 layer in CIGS solar cells is based primarily on mechanical methods. It using laser processing to be reach best accuracy and size demand for mechanical equipment, laser processing is rapid, processing line wide relatively small and edge chip fewer advantages [1–3]. Jafari et al. [4] show that Tin on stainless steel substrates has a good capability for tokamak first wall due to its fine grain structure, high reflectivity, and hardness property. Li et al. [5] used a novel process method for the fabrication of DARC consisting of SiNx:H using PECVD and SiO2 films deposited using electron-beam evaporation. Walker et al. [6] proposed a new triple-junction solar cell (3J) exploiting the highly absorptive I–III–VI chalcopyrite CuInSe2 material as an alternative to III–V semiconductor 3J solar cells. Patidar et al. used monodispersed ZnO nanoparticles to fabricate P3HT/ZnO solar cells [7]. S. Zhao and C. Zhao [8] used transmission electron microscopy to observe the microstructure of boundaries between the matrix and G.P. zone in Ti-rich Ni-Ti alloy. Hsu et al. [9] developed a model using interpretive structural modeling (ISM), benefits, opportunities, costs, and risks (BOCR), and fuzzy analytic network process (FANP) to aggregate the opinions of experts in evaluating available solar cell technologies.Huang et al. [10] developed a nanooxidation and wet etching technique to produce nanostructures on TiAlN film. Krishna et al. [11] proposed a new technique for the measurement of solar cell blanket temperature. The enhanced solar cell efficiency in multilevel rectangular, arbitrary gratings by Lin and Phillips can be attributed to improved optical coupling and light trapping across the solar spectrum [12]. Zhao and Jiang [13] studied the room temperature UV emission of ZnO films with various defect densities fabricated using a KrF laser irradiation process. Chen et al. [14] simulated the Gaussian distribution of laser irradiation on the preprocessor structure. A UV laser processing system produced micropatterns on ITO thin films to identify the conditions that could damage the substrates. Dai et al. [15] presented a new approach to the development of GaN-based devices using the 157 nm DUV laser for microfabrication.D. Chen and M. Chen [16] used ANSYS simulation software for the analysis of a UV (355-nm) laser processing system. According to the simulation results, the laser function time was 135 μs, the UV laser was 0.5 W, and the P2 layer thin films were removed. Furthermore the maximum temperature at the surface of the material reached 2795°C using laser power of 0.5 W, at which point the P2 layer material reached gasification temperature. The study focus was increasing laser scribing P2 layer phenomena understandability. The experiment results confirmed that the laser apparatus is effective when applied to a stainless steel CIGS solar cell P2 layer.


## 2. Experimental Principle and Materials

Figure1 presents the laser process route. The UV laser primarily applies a high accuracy microelectronic product, semiconductor, LED, and LCD process. Figure 2 presents the UV laser processing machine used in this study. A glass base plate of stainless steel was used in this study. The CIGS plates films have SiO2 layer, molybdenum electrode, CIGS absorbed layer, CdS buffered layer, i-ZnO penetrate light layer, TCO front electrode, MgF resisting reflected materials, and direct electrode materials. Figure 3 presents a diagram of the laser solar cell film. The diagram included P1, P2, and P3 layer for solar cell film materials.Figure 1
Illustration of laser process route [16].Figure 2
UV laser processing machine of the study laboratory [16].Figure 3
Diagram of the laser solar cell film [16].


## 3. Experimental Procedure

This study uses laser UV (355 nm) for the vehicle that used CIGS thin-film solar cells in the P2 layer scribing processing. The first stage was the characterization of the laser and laser system parameters. The second stage involved preparation of materials. Sputtering and chemical deposition were used in the fabrication of specimens. The third stage involved laser scribing of the P2 layer by altering the focus position, energy density, and scanning velocity. A 3D confocal laser scanning microscope was used to measure the width and depth of P2 layer.


## 4. Results and Discussion

Lasers can be used to scribe the P2 layer in CIGS thin-film solar cells; the main allows the laser heat source to remove molten layer P2 to achieve the insulation effect. But they cannot be used to remove the SiO2 film.


### 4.1. Scribing Results at Different Focus Position

The studies understand different situations of focusing position for workpiece scribing influence. In the experiment, scanning velocity is fixed and laser pulse frequency is fixed at 40 kHz and laser energy is fixed at 0.4 W which change focus position to scribing specimen. We employed a confocal microscope to examine the results of scribing. Figure4 shows focus position, that is, (a) perpendicularity, (b) minus leave perpendicularity, and (c) positive leave perpendicularity. From scribing results, obvious laser scribing width and depth, respectively, can be seen: (a) W=29.481 μm and h=5.215 μm, (b) W=71.326 μm and h=0.950 μm, and (c) W=67.522 μm and h=0.987 μmm. It can hit through P2 layer when energy gives 0.05 W, because UV laser machine is very unstable when having lower energy and scribing line produces heat influence area and smaller line width as shown in Figure 4(a). The scribing results are straight line and larger width under minus leave perpendicularity and positive leave perpendicularity as shown in Figures 4(b) and 4(c).Figure 4
UV laser focus position. (a) Perpendicularity, (b) minus leave perpendicularity, and (c) positive leave perpendicularity.
(a)
(b)
(c)


### 4.2. Scribing Results Obtained Using Various Energy Density Levels

We employed a confocal microscope to examine the results of scribing with the following laser energy levels: (a) 0.4 W, (b) 0.5 W, (c) 0.6 W, and (d) 0.7 W. Figure5 shows EDS analysis results after scribing the P2 membrane layer with a UV laser set at various energy density levels. As shown in Figure 5, a large number of granules can be seen along the edge due to the numerous materials with which the P2 layer is composed. It can be seen that UV laser process produced Cr, Fe, and Se chemical composition because SiO2 penetrate rate is very similar to glass and induced Cr and Fe chemical elements.Figure 5
Scribing P2 layer membrane composition analysis result using different UV laser energy density.
(a)
Laser energy 0.4 W. Atomic% O = 41.70, Si = 13.21, Fe = 45.08
(b)
Laser energy 0.5 W. Atomic% O = 41.25, Si = 13.60, Fe = 44.45, Se = 0.70
(c)
Laser energy 0.6 W. Atomic% O = 42.19, Si = 12.90, Fe = 43.16, Se = 1.74
(d)
Laser energy 0.7 W. Atomic% O = 36.97, Si = 11.68, Cr = 9.30, Fe = 41.07, Se = 0.98


### 4.3. Scribing Results Obtained at Various Scanning Velocities

Figure6 used various scanning velocities for UV laser scribing P2 layer. The figure used positive leave perpendicularity and frequency is fixed at 60 kHz and laser energy is fixed at 0.6 w. The study only changes laser scribing velocity to finish the specimen depth and width; it can be seen that no larger difference result using CCD microscope to watch specimen was found.Figure 6
UV laser scribing P2 layer at different scan velocity.The laser scribing has finished 3D confocal microscope to measure the specimen. Figure7 shows UV lasers using different scanning velocities scribing P2 film on 3D confocal microscope, including 100~900 mm/s, respectively. No obvious influence on depth and width for different scanning velocities can be seen.Figure 7
Illustration of UV lasers using different scanning velocities for scribing P2 film on 3D confocal microscope.Figure8 shows relationship diagram of UV laser scanning velocities and underline depth. It can be seen that laser scanning velocities at 10~1000 mm/s underline width about 0.96 μm~1.07 μm.Figure 8
Relationship diagram of UV laser scanning velocities and underline depth.


## 4.1. Scribing Results at Different Focus Position

The studies understand different situations of focusing position for workpiece scribing influence. In the experiment, scanning velocity is fixed and laser pulse frequency is fixed at 40 kHz and laser energy is fixed at 0.4 W which change focus position to scribing specimen. We employed a confocal microscope to examine the results of scribing. Figure4 shows focus position, that is, (a) perpendicularity, (b) minus leave perpendicularity, and (c) positive leave perpendicularity. From scribing results, obvious laser scribing width and depth, respectively, can be seen: (a) W=29.481 μm and h=5.215 μm, (b) W=71.326 μm and h=0.950 μm, and (c) W=67.522 μm and h=0.987 μmm. It can hit through P2 layer when energy gives 0.05 W, because UV laser machine is very unstable when having lower energy and scribing line produces heat influence area and smaller line width as shown in Figure 4(a). The scribing results are straight line and larger width under minus leave perpendicularity and positive leave perpendicularity as shown in Figures 4(b) and 4(c).Figure 4
UV laser focus position. (a) Perpendicularity, (b) minus leave perpendicularity, and (c) positive leave perpendicularity.
(a)
(b)
(c)


## 4.2. Scribing Results Obtained Using Various Energy Density Levels

We employed a confocal microscope to examine the results of scribing with the following laser energy levels: (a) 0.4 W, (b) 0.5 W, (c) 0.6 W, and (d) 0.7 W. Figure5 shows EDS analysis results after scribing the P2 membrane layer with a UV laser set at various energy density levels. As shown in Figure 5, a large number of granules can be seen along the edge due to the numerous materials with which the P2 layer is composed. It can be seen that UV laser process produced Cr, Fe, and Se chemical composition because SiO2 penetrate rate is very similar to glass and induced Cr and Fe chemical elements.Figure 5
Scribing P2 layer membrane composition analysis result using different UV laser energy density.
(a)
Laser energy 0.4 W. Atomic% O = 41.70, Si = 13.21, Fe = 45.08
(b)
Laser energy 0.5 W. Atomic% O = 41.25, Si = 13.60, Fe = 44.45, Se = 0.70
(c)
Laser energy 0.6 W. Atomic% O = 42.19, Si = 12.90, Fe = 43.16, Se = 1.74
(d)
Laser energy 0.7 W. Atomic% O = 36.97, Si = 11.68, Cr = 9.30, Fe = 41.07, Se = 0.98


## 4.3. Scribing Results Obtained at Various Scanning Velocities

Figure6 used various scanning velocities for UV laser scribing P2 layer. The figure used positive leave perpendicularity and frequency is fixed at 60 kHz and laser energy is fixed at 0.6 w. The study only changes laser scribing velocity to finish the specimen depth and width; it can be seen that no larger difference result using CCD microscope to watch specimen was found.Figure 6
UV laser scribing P2 layer at different scan velocity.The laser scribing has finished 3D confocal microscope to measure the specimen. Figure7 shows UV lasers using different scanning velocities scribing P2 film on 3D confocal microscope, including 100~900 mm/s, respectively. No obvious influence on depth and width for different scanning velocities can be seen.Figure 7
Illustration of UV lasers using different scanning velocities for scribing P2 film on 3D confocal microscope.Figure8 shows relationship diagram of UV laser scanning velocities and underline depth. It can be seen that laser scanning velocities at 10~1000 mm/s underline width about 0.96 μm~1.07 μm.Figure 8
Relationship diagram of UV laser scanning velocities and underline depth.


## 5. Conclusion

This study used UV laser to scribe on CIGS thin-film P2 layer. The simulation and experiment obtained the following several conclusions.(1)
The scribing results are straight line and larger width under minus leave perpendicularity and positive leave perpendicularity.(2)
UV laser process produced Cr, Fe, and Se chemical composition because SiO2 penetrate rate is very similar to glass and induced Cr and Fe chemical elements.(3)
The laser scanning velocities at 10~1000 mm/s underline width about 0.96μm~1.07 μm.The experiment results confirm the effectiveness of the laser apparatus when applied to a stainless steel CIGS solar cell P2 layer.



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*Source: 894673-2015-06-24.xml*