Artist Photovoltaic Modules - MDPI

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Jul 15, 2016 - Department of Materials Science and Engineering, Da-Yeh ... skylights [7–9], and other areas that require transparency and electricity ...
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Artist Photovoltaic Modules Shui-Yang Lien Department of Materials Science and Engineering, Da-Yeh University, Changhua 51591, Taiwan; [email protected]; Tel.: +886-04-851-1888 (ext. 1760) Academic Editor: Narottam Das Received: 23 May 2016; Accepted: 11 July 2016; Published: 15 July 2016

Abstract: In this paper, a full-color photovoltaic (PV) module, called the artist PV module, is developed by laser processes. A full-color image source is printed on the back of a protective glass using an inkjet printer, and a brightened grayscale mask is used to precisely define regions on the module where colors need to be revealed. Artist PV modules with 1.1 ˆ 1.4 m2 area have high a retaining power output of 139 W and an aesthetic appearance making them more competitive than other building-integrated photovoltaic (BIPV) products. Furthermore, the installation of artist PV modules as curtain walls without metal frames is also demonstrated. This type of installation offers an aesthetic advantage by introducing supporting fittings, originating from the field of glass technology. Hence, this paper is expected to elevate BIPV modules to an art form and generate research interests in developing more functional PV modules. Keywords: building-integrated photovoltaic (BIPV); full-color; laser process; photovoltaic (PV) module

1. Introduction Building-integrated photovoltaics (BIPVs) have attracted increasing attention in recent years because of their efficient use of space and effective energy production [1,2]. Conventional silicon wafer-based solar cells have high optoelectronic conversion efficiency, but can only be integrated on rooftops because of limitations brought about by their opaque appearance. The development of semi-transparent, thin-film amorphous silicon (a-Si) or microcrystalline silicon (µc-Si) solar cells expands the applications of solar cells to glass-related technologies and products such as windows [3–6], skylights [7–9], and other areas that require transparency and electricity generation. Modules with 10%–50% transmittance are commercially available, and are fabricated through the ablation of films on the modules [10–14]. However, BIPVs have a small market share nowadays, mainly because of limited aesthetic choices. One survey shows that more than 85% of architects believe that aesthetic concerns increase photovoltaic (PV) system installations even with reduced conversion efficiencies [15]. Access to efficient PV modules with a variety of colors is highly desirable to further increase user acceptance and the installation rate. Existing literatures [16–19] proposed several approaches for fabricating colored Si-based PV modules, but these modules can only display a single color, and thus give a dull appearance. To overcome challenges of color presentation, we have developed artist PV modules, which are colorful and semi-transparent. The key features of the modules are the provision of a color image source by a back protective glass, and color visualization by using laser processes with a brightened grayscale mask. In this paper, the structures of artist PV modules and the related laser scribing mechanism are first described. Effects of the mask on solar cell conversion efficiency are investigated. Furthermore, characteristics of a scaled, full-color a-Si/µc-Si tandem PV module are presented for comparison with commercial Si-based thin-film BIPV products. Finally, practical applications and installation details of the PV modules as curtain walls are discussed.

Energies 2016, 9, 551; doi:10.3390/en9070551

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2. Experimental Methods 2.1. Fabrication of Artist Photovoltaic Modules The schematic structure of artist PV modules is shown in Figure 1a. The module consists of a PV submodule at the front and a protective glass at the back. The fabrication process was described below. The submodule was series-connected by standards P1 to P3 laser processes [20]. Then a custom image was ink-jet-printed on the back glass in full color, and printed on a transparent sticker with adjustments, as shown in Figure 1b. The image was converted to grayscale (from A to A’) according to the luminosity method formula [21]: Gray “ 0.21R ` 0.71G ` 0.07B

(1)

where R, G, and B are the intensities of the red, green, and blue colors of the pixel, respectively. The percentage values indicated on the grayscale image were the transmittance Tm . Afterwards, the brightness of the grayscale image was increased by 40% or above (from A’ to A”). The transparent sticker with the brightened grayscale image was stuck on the glass side of the submodule as a mask for the subsequent 532 nm laser process (herein denoted as P4 laser scribing), which scanned line-by-line over the submodule. The spacing of the laser line was about 0.4 mm. It should be noted that if the mask was only converted to grayscale but not brightened, many color pixels would change to heavy gray. The resultant patterned image on the submodule would be also grayscale, but when it encapsulated with the back glass, the full-color image on the latter could hardly be observable from the submodule side. The brightening allowed the P4 laser to remove the regions on the submodule where the colors need to be revealed, so the image could be seen from the both sides of the module. All the laser processes were performed through the glass side of the submodule, and the detailed laser parameters are summarized in Table 1. Finally, the scribed submodule was encapsulated with the back glass in ethylene vinyl acetate (EVA) to finish the fabrication of the artist PV module. In addition, the ink on the back glass was ultraviolet (UV)-resistant to inhibit fade and discoloration. The durability of the inks was more than 10 years. Brightened grayscale image Front module

Transparent sticker Glass Silicon PV layers EVA Full-color image Back protective glass (a) Figure 1. Cont.

81%

91%

73% 65%

55%

A

43%

39% 24%

28%

Grayscale (b)

100%

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49% 70%

A’

27% 14%

Image source

100%

100%

92% 77%

A’’

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55% 42%

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Brightened grayscale

EVA Full-color image Back protective glass (a)

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73% 65%

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Grayscale (b)

Figure 1. (a) The schematic structure of the full-color artist photovoltaic (PV) modules; and (b) a comparison of the masks in our previous work (gray scale) and the present work (brightened gray scale). The indicated percentage values are the gray transmittance of the corresponding pixels.

Figure 1

Table 1. Laser parameters used for P1, P2, P3 and P4 processes. Parameter

P1

P2

P3

P4

Wavelength (nm) Focal length (mm) Power (W) Line width (µm) Velocity (mm/s) Pulse frequency (Hz)

1064 18 5 30 350 20

532 27 0.25 29.8 400 16

532 27 0.35 42 325 12

532 37 0.6 40 400 18

As the mask image might consist of various pixels with different Tm after being converted to brightened grayscale, individual investigation for each pixel is essential to clarify their impacts on the submodules. Five submodules (5 cm ˆ 5 cm) and masks with Tm = 20%, 40%, 60%, 80% and 100% Energies 2016, 9, 551 3 of 8 were prepared. Mask transmittance was confirmed by UV-visible spectroscopy (Titan Electro-Optics Co. were Ltd., prepared. Taipei, Taiwan) at a wavelength of 532 by nm with anspectroscopy error of less(Titan thanElectro-Optics 5% as shown in Mask transmittance was confirmed UV-visible Co.2.Ltd., Taiwan) of at athe wavelength of 532 nm observed with an error of less scanning than 5% aselectron shown inmicroscope Figure Figure TheTaipei, morphology submodules was through 2. and The optical morphology of the submodules was observed scanning electron (SEM)of the (SEM) microscope (OM) (M&T Optics Co. through Ltd., Taipei, Taiwan). Themicroscope depth profiles and optical microscope (OM) (M&T Optics Co. Ltd., Taipei, Taiwan). The depth profiles of thescribe scribes were obtained using an alpha profilometer (KTA Tencor, Milpitas, CA, USA). The laser scribes were obtained using an alpha profilometer (KTA Tencor, Milpitas, CA, USA). The laser width was evaluated by the full-width at half maximum value of the scribe. The current-voltage (I-V) scribe width was evaluated by the full-width at half maximum value of the scribe. The characteristics of the modules were measured at AM1.5G (1000 W/m2 ) using a solar simulator. The current-voltage (I-V) characteristics of the modules were measured at AM1.5G (1000 W/m2) using a stabilized power output of the PV modules was determined by a standard light soaking test according solar simulator. The stabilized power output of the PV modules was determined by a standard light to IEC 61646test [22]according at 60 ˝ C to forIEC 1000 h. [22] at 60 °C for 1000 h. soaking 61646

Figure 2. Transmittance spectra of the masks with Tm = 20%, 40%, 60%, 80%, and 100%.

Figure 2. Transmittance spectra of the masks with Tm = 20%, 40%, 60%, 80%, and 100%.

2.2. Mechenism of P4 Laser-Scribing Process for Image Patterning The mechanism of P4 scribing is based on the laser energy intensity of the Gaussian distribution [23] and Beer’s law [11]: α



e

(2)

Figure 2. Transmittance spectra of the masks with Tm = 20%, 40%, 60%, 80%, and 100%. Energies 2016, 9, 551

2.2. Mechenism of P4 Laser-Scribing Process for Image Patterning

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The2.2. mechanism ofP4P4Laser-Scribing scribing isProcess basedfor onImage the laser energy intensity of the Gaussian distribution Mechenism of Patterning [23] and Beer’s law [11]: The mechanism of P4 scribing is based on the laser energy intensity of the Gaussian distribution [23] and Beer’s law [11]:

α I “ Tm α

e x2

P 2π



2

e

2R0 2

(2) q

(2)

1 2πR0 ˆ ln ˙ , for (3) ´1α Ith d“ ln , for I ą Ith (3) α I where I is the laser energy intensity after passing the mask, α is the absorptivity, P is the laser where I is the laser energy intensity after passing the mask, α is the absorptivity, P is the laser power, power, R0 is the laser spot radius, x is the distance across scribes, Ith is the ablation threshold R0 is the laser spot radius, x is the distance across scribes, Ith is the ablation threshold intensity of intensitysilicon of silicon films, d is the scribe depth. The mask decrease laser films, and d is and the scribe depth. The grayscale maskgrayscale will decrease laser will intensity depending onintensity depending on Tm, leading therebyto leading to various scribing depths, as schemed in Figure 3. We Tm , thereby various scribing depths, as schemed in Figure 3. We applied this concept to applied pattern the image from the mask to the PV module. this concept to pattern the image from the mask to the PV module.

Figure 3.Figure Theoretical calculation results intensityand and ablation depth distribution across the 3. Theoretical calculation resultsofoflaser laser intensity ablation depth distribution across the scribes for submodules withoutmask. mask. scribes for submodules withwith andand without 3. Results and Discussion The OM and SEM topological images, as well as the depth profiles, of the scribes for mask transmittances (Tm ) of 100%, 80%, 60%, 40%, and 20% are shown in Figure 4. The case of Tm = 100% shows round laser spots (Figure 4a1,a2,b1,b2) and straight side walls on the scribes (Figure 4a3,b3). This result indicates that laser intensity is not significantly affected by the mask. As Tm decreases, film delamination and spot-size distortion occur at the edges of the scribes (Figure 4d1,d2,e1,e2). The shape of the scribe changes from U to V as the depth and width decrease. Tm below 20% did not lead to film ablation. This phenomenon can be explained by the fact that after passing the mask, the laser intensity value was lower than the a-Si threshold ablation, typically 0.4 J/cm2 [24]. From these results, masks with high Tm lead to fewer deviations from optimal laser conditions, thus having lower electrical loss [23]. However, the use of high Tm masks results in the increased removal of films in the effective area of the modules. These two factors are the trade-offs in determining the final device performance.

to film ablation. This phenomenon can be explained by the fact that after passing the mask, the laser intensity value was lower than the a-Si threshold ablation, typically 0.4 J/cm2 [24]. From these results, masks with high Tm lead to fewer deviations from optimal laser conditions, thus having lower electrical loss [23]. However, the use of high Tm masks results in the increased removal of films in the effective Energies 2016,area 9, 551of the modules. These two factors are the trade-offs in determining the final 5 of 9 device performance.

Figure 4. The optical microscope (OM) (top) and scanning electron microscope (SEM) (middle) Figure 4. The optical microscope (OM) (top) and scanning electron microscope (SEM) (middle) images, images, and depth profiles (bottom) for Tm = 20%, 40%, 60%, 80% and 100% of a-Si PV modules. and depth profiles (bottom) for Tm = 20%, 40%, 60%, 80% and 100% of a-Si PV modules.

The effects of the mask on the a-Si submodule performance such as short-circuit current density The effects ofvoltage the mask the factor a-Si submodule performance such as short-circuit current density (Jsc), open-circuit (Vocon ), fill (FF), and conversion efficiency (η) are shown in Figure 5a. (J open-circuit voltage (V and conversion efficiency are shown Figure 5a. sc ), original oc ), fill factor The submodule (without the P4(FF), process) is also indicated as a(η)reference forincomparing The original submodule process) is also indicated as a reference comparing power power reduction values.(without It can be the seenP4that Jsc almost remains unchanged when for Tm increases from 0% reduction values. It can be seen that J almost remains unchanged when T increases from 0% to sc m 2 2 to 20%, and decreases from 2.45 mA/cm to 2.1 mA/cm with the increase of Tm from 20% to 100%. 2 to 2.1 mA/cm2 with the increase of T from 20% to 100%. The 20%, and decreases from 2.45 mA/cm m The reduction in Jsc is attributed to optical loss caused by the ablation of the active layers. Voc and FF reduction in Jsctrends. is attributed to optical loss caused by thevalues ablation active layers. V oc deteriorating and FF show show similar Tm = 40% and 60% have lower as of a the consequence of the similar Tm =resulting 40% and η60% have valuesfor as T a mconsequence of the deteriorating surface surface trends. states. The value is lower the lowest = 100%. Therefore, although grayscale states. The resulting η value is the lowest for T = 100%. Therefore, although grayscale design may m design may lead to a reduction in Voc and FF, the module still has higher performance than T m = lead to a reduction in V and FF, the module still has higher performance than T = 100%. These oc m 100%. These results are still validated in the case of a-Si/µc-Si tandem solar cells (Figure 5b). It results validated in the case of a-Si/µc-Si cells (Figure should be noted should are be still noted that a module with Tm = 100%tandem can be solar analogized to the5b). 10%It semi-transparent that a module with T = 100% can be analogized to the 10% semi-transparent module, the artist m module, while the artist module is a combination of Tm = 0%–100%. The latter could while be assumed to module is a combination of T = 0%–100%. The latter could be assumed to have higher, or at least m have higher, or at least equal, performance than the 10% semi-transparent module. equal,A performance than the 10% Energies 9, 551 5 ofits 8 I-V fifth2016, generation-sized (1.1semi-transparent × 1.4 m2) artist module. a-Si/µc-Si PV module is fabricated, and characteristics are compared to that of the opaque and 10% semi-transparent modules as shown in Figure 6. Each of the PV modules was fabricated under identical laser conditions. The result matches Figure 5, which confirms the expectation that the full-color module is more competitive than the 10% semi-transparent PV module. A stable power output of 126 W (14.2% reduction) of the artist PV module is achieved, while the 10% semi-transparent module shows a 123 W (16.3% reduction) stabilized power output. We further increase the performance from 126 W to 139 W for the artist module and 123–134 W for the 10% semi-transparent module when using a higher performance of 160 W of the opaque submodules (NexPower Tech. Corp., Taichung, Taiwan).

Figure 5. External parameters of (a) a-Si and (b) a-Si/µc-Si submodules with different Tm values.

Figure 5. External parameters of (a) a-Si and (b) a-Si/µc-Si submodules with different Tm values. The The denoted reference is the submodule without the P4 laser process. denoted reference is the submodule without the P4 laser process.

Energies 2016, 9, 551 Figure 5. External parameters of (a) a-Si and (b) a-Si/µc-Si submodules with different Tm values.

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The denoted reference is the submodule without the P4 laser process.

Figure 6. Current-voltage (I-V) characteristics of opaque, 10% semi-transparent and artist a-Si/µc PV modules. Figure 6. Current-voltage (I-V) characteristics of opaque, 10% semi-transparent and artist a-Si/µc PV modules.

The 160 W opaque, 134 W 10% semi-transparent and 139 W artist PV modules were installed with different orientations and tilt angles with respect to the ground in Changhua, Taiwan, for one A fifth (1.1 ˆ 1.4 m2 ) outside artist a-Si/µc-Si PV module fabricated, andpoint its I-V year from generation-sized 2014. The modules were placed and connected with a is maximum power characteristics are that compared to the thatpower of the opaque 10% semi-transparent shown tracking inverter recorded output. Theand irradiance was measured bymodules an opticalaspower in meter. FigureThe 6. Each of the PV modules was fabricated identical laser conditions. The result weather condition was changeable, but theunder total irradiance was about equal to 1299.4 peak sun hours 3.56 h/day). Figure 7 shows power generation forcompetitive the three matches Figure 5, (average which confirms the expectation thatthe theannual full-color module is more modules; the capacity of each PV module is normalized to 1 kW. In allofthe cases the annual power of than the 10% semi-transparent module. A stable power output 126 W (14.2% reduction) the highest for the opaque PV 10% module and the lowestmodule for the 10% semi-transparent thegeneration artist PV is module is achieved, while the semi-transparent shows a 123 W (16.3% module. stabilized Despite having same We installation capacity,the theperformance three types of modules reduction) powerthe output. further increase from 126 W have to 139different W for the annual power generation due to different performance under variable illumination irradiances over artist module and 123–134 W for the 10% semi-transparent module when using a higher performance 2), the module performance depends on the a day. Particularly for weak light illumination (≤200 W/m of 160 W of the opaque submodules (NexPower Tech. Corp., Taichung, Taiwan). shunt [25], which calculated as the inverse themodules point ofwere V = 0installed in the I-V The resistance 160 W opaque, 134 W can 10%be semi-transparent and 139 Wslope artistatPV with curve. The calculated shunt resistances for the opaque, artist PV, and the 10% transmittance modules different orientations and tilt angles with respect to the ground in Changhua, Taiwan, for one year are 4139, 3468, and 3003 Ω, respectively. Compared to the 10% semi-transparent modules, artist PV from 2014. The modules were placed outside and connected with a maximum power point tracking inverter that recorded the power output. The irradiance was measured by an optical power meter. The weather condition was changeable, but the total irradiance was about equal to 1299.4 peak sun hours (average 3.56 h/day). Figure 7 shows the annual power generation for the three modules; the capacity of each module is normalized to 1 kW. In all the cases the annual power generation is the highest for the opaque PV module and the lowest for the 10% semi-transparent module. Despite having the same installation capacity, the three types of modules have different annual power generation due to different performance under variable illumination irradiances over a day. Particularly for weak light illumination (ď200 W/m2 ), the module performance depends on the shunt resistance [25], which can be calculated as the inverse slope at the point of V = 0 in the I-V curve. The calculated shunt resistances for the opaque, artist PV, and the 10% transmittance modules are 4139, 3468, and 3003 Ω, respectively. Compared to the 10% semi-transparent modules, artist PV modules have a smaller laser ablation area and therefore higher shunt resistance. The non-tilted modules show a power generation of around 1354, 1288 and 1185 kW for opaque, artist PV, and 10% semi-transparent modules, respectively. The 23.5˝ -tilted modules show about 4%–5% reduction in power generation, except for the modules facing south, showing even higher performance than non-tilted ones. This can be related to improvement in plane-of-array irradiance. A significant reduction in power generation is observed for the 90˝ -tilted modules. Power generations of 600–800 W, approximately half of that of 0˝ - and 23.5˝ -tilted modules, are obtained.

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modules show a power generation of around 1354, 1288 and 1185 kW for opaque, artist PV, and 10% semi-transparent modules, respectively. The 23.5°-tilted modules show about 4%–5% reduction in modules have a smaller laser ablation area and therefore higher shunt resistance. The non-tilted power generation, exceptgeneration for the modules south, higherartist performance than modules show a power of aroundfacing 1354, 1288 andshowing 1185 kW even for opaque, PV, and 10% non-tilted ones. This can berespectively. related to The improvement plane-of-array irradiance. A significant semi-transparent modules, 23.5°-tilted in modules show about 4%–5% reduction in reduction in power generation is observed for the 90°-tilted modules. Power generations of 600–800 Energies 2016, 9, 551 7 of 9 power generation, except for the modules facing south, showing even higher performance than W,non-tilted approximately half of that of 0°and 23.5°-tilted modules, are obtained. ones. This can be related to improvement in plane-of-array irradiance. A significant reduction in power generation is observed for the 90°-tilted modules. Power generations of 600–800 W, approximately half of that of 0°- and 23.5°-tilted modules, are obtained.

Figure 7. 7. Annual and artist artist PV PV modules modules installed installed Figure Annual power power generation generation of of opaque, opaque, 10% 10% semi-transparent semi-transparent and with different tilt angles angles and orientations. The PV PV modules are installed installed in Changhua, Taiwan. Figure 7. Annual powerand generation of opaque, 10% semi-transparent andin artist PV modules installed with different tilt orientations. The modules are Changhua, Taiwan. with different tilt angles and orientations. The PV modules are installed in Changhua, Taiwan.

Figure 8 demonstrates the installation of the artist PV modules, wherein four modules are Figure 8 demonstrates the installation of the artist PV modules, wherein four modules are Figure 8 demonstrates installation the artist modules, wherein four modules supported tightly by glass the fittings at the ofcorners of PV each module. The modules are are tilted supported tightly by glass fittings at the corners of each module. The modules are tilted approximately supported tightly by glass fittings at the corners of each module. The modules are tilted approximately 90° to the horizontal. This installation method has been widely used in traditional 90˝ to the horizontal. This installation method has been widely used in traditional glass curtain walls, approximately 90° and to theis horizontal. has been widely usedofinmetal traditional glass curtain walls, engineeredThis for installation safety andmethod strength without the need frames and is engineered for safety and strength without the need of metal frames (which can block the view) glass can curtain walls, and istoengineered safety and strength without the need of metal frames (which block the view) offer visualfor beauty. to (which offer visual beauty. can block the view) to offer visual beauty.

Figure Annualpower powergeneration generationof ofopaque, opaque, 10% modules installed Figure 8. 8. Annual semi-transparent andartist artistPV PV modules installed Figure 8. Annual power generation of opaque, 10% semi-transparent semi-transparentand and artist PV modules installed with different tilt angles and orientations. The PV modules are installed in Changhua, Taiwan. with different different tilt tilt angles angles and and orientations. orientations. The The PV modules modules are are installed installed in in Changhua, Changhua, Taiwan. Taiwan. with

We introducethis thismethod method from from the the field field of of glass certain We introduce glass to to BIPV BIPV technology technologywhile whilesolving solving certain We introduce this method from the field of glass to BIPVinstalled technology while solving certain problems described as follows. Figure 9a shows the glass fittings in traditional glasses and problems described as follows. Figure 9a shows the glass fittings installed in traditional glasses and problems described as follows. Figure 9a shows the glass fittings installed in traditional glasses and BIPV modules. The most cost-effective method for glass fittings is to drill holes from the back to the front, and then to use screws (Figure 9b). However, this is not suitable for BIPV modules as the holes drilled on the PV modules can deteriorate performances, and the holes expose the module to a high risk of water leakage. Hence, we only drilled holes on the corners of the back glass, and inserted alternative routels into the holes (Figure 9c). The back glass was then EVA-laminated with

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BIPV modules. The most cost-effective method for glass fittings is to drill holes from the back to the front, and then to use screws (Figure 9b). However, this is not suitable for BIPV modules as the holes Energies 2016,on 9, 551 8 of 9 drilled the PV modules can deteriorate performances, and the holes expose the module to a high risk of water leakage. Hence, we only drilled holes on the corners of the back glass, and inserted alternative routels into the holes (Figure 9c). The back glass was then EVA-laminated with the PV the modules. PV modules. would penetrate back glass through holes theroutels routelsafter after The The EVAEVA would penetrate the the back glass through thethe holes to to fixfixthe encapsulation. This method prevents module damage and water leakage. Finally, PV curtain walls encapsulation. This method prevents module damage and water leakage. Finally, PV curtain walls withwith highhigh aesthetic quality cancan bebe built. aesthetic quality built.

(a)

(b)

(c)

Figure 9. (a) Installation of artist PV modules with glass routels, and a comparison of the routels used Figure 9. (a) Installation of artist PV modules with glass routels, and a comparison of the routels used in (b) traditional glass; and (c) artist PV modules. EVA: ethylene vinyl acetate. in (b) traditional glass; and (c) artist PV modules. EVA: ethylene vinyl acetate.

4. Conclusions 4. Conclusions We have demonstrated a full-color, semi-transparent artist PV module using laser processes We have demonstrated a full-color, semi-transparent artist module with a brightened grayscale mask that precisely defines the PV regions thatusing needlaser to beprocesses removedwith or a brightened grayscale mask that precisely theofregions that need to befrom removed or retained. retained. This work can be regarded as an defines evolution BIPV module designs plain and simple Thistowork can beaesthetic. regardedFurthermore, as an evolution BIPV modulepower designs fromof plain simple tofull-color extremely extremely theof high retaining output 139 and W makes the aesthetic. the high retaining power output of 139 W makesmodules. the full-color more moduleFurthermore, more competitive than other commercial semi-transparent This module technique is expected than to break stereotypesemi-transparent that solar cells are only forThis power generation, and can competitive otherthe commercial modules. technique is expected to possibly break the elevate that PV products into art form. stereotype solar cells areanonly for power generation, and can possibly elevate PV products into an art form.

Acknowledgments: This work is sponsored by the Ministry of Science and Technology of the Republic of China under Contract Nos. andMinistry 104-2632-E-212-002. Acknowledgments: This104-2221-E-212-002-MY3 work is sponsored by the of Science and Technology of the Republic of China under Contract Nos. 104-2221-E-212-002-MY3 and 104-2632-E-212-002. Conflicts of Interest: The authors declare no conflict of interest. Conflicts of Interest: The authors declare no conflict of interest.

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