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Microfluidic sealing and housing system for innovative dye-sensitized solar cell architecture
Microelectronic Engineering 88 (2011) 2308–2310
Contents lists available at ScienceDirect
Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee
Microfluidic sealing and housing system for innovative dye-sensitized solar cell architecture A. Lamberti a,b,⇑, A. Sacco a,b, S. Bianco a, E. Giuri b, M. Quaglio a, A. Chiodoni a, E. Tresso b a b
Center for Space Human Robotics, Italian Institute of Technology (IIT), C.so Trento 21, IT-10129 Torino, Italy Materials Science and Chemical Engineering Department, Politecnico di Torino, C.so Duca degli Abruzzi 24, IT-10129 Torino, Italy
a r t i c l e
i n f o
Article history: Received 14 September 2010 Accepted 30 December 2010 Available online 5 January 2011 Keywords: Dye-sensitized solar cells Microfluidics Clamping Housing
a b s t r a c t Dye-sensitized solar cells (DSSCs) have received great attention over the past decade for their high energy conversion efficiency, relatively easy fabrication process and low production cost. However, at present, some practical difficulties such as solvent evaporation, leakage of liquid electrolyte and sealing stability remain serious obstacles to their convenient application. An innovative microfluidic DSSC housing system is here proposed. Sealing performances of such architecture were examined by dynamic fluidic tests and good sealing for pressure up to 50 kPa and temperature of 80 °C was obtained, avoiding leakages and bubble formation. Current–voltage and impedance spectroscopy measurements were used to determine the photovoltaic performance of the cell. Results were compared to the ones obtained with DSSC prototypes assembled in our laboratory following a standard procedure, and higher efficiency values have been obtained. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Solar energy plays a key role in the green economy scenario, and DSSCs have emerged during the last 20 years as one of the most promising approach for a new generation of solar devices [1]. The use of cheap materials and easy fabrication processes and technologies makes them suitable as a low cost solution compared to silicon-based cells, even if they currently show moderate conversion efficiency. In a conventional cell, the photoanode consists of a relatively thick (around 8 lm) layer of TiO2 nanoparticles, electrically interconnected thanks to a sintering process and subsequently sensitized with dye molecules (usually Ru complexes). The TiO2 layer is deposited on a glass slice, covered with transparent conducting oxide (TCO) for electrical contact purposes. A I =I3 redox couple acts as hole conductor, electrically regenerating the dye molecules. The counter electrode consists again on a TCO-covered glass slice with a thin (few nm) layer of Pt, to promote the reduction of the triiodide. Different manufacturing solutions have been proposed for highly performant DSSCs, such as advanced print screen techniques, electrolyte filling and dye profiling machines [2]. As housing for the standard electrochemical cell, the couple of glass slices
⇑ Corresponding author at: Center for Space Human Robotics, Italian Institute of Technology (IIT), C.so Trento 21, IT-10129 Torino, Italy. Tel.: +390110903413. E-mail address: [email protected] (A. Lamberti). 0167-9317/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2010.12.114
are sealed with thermoplastic hot melt glue, creating a free space that is completely filled with electrolyte solution [3,4]. However in research laboratories, where the need is for simple and quick prototypes fabrication, the assembly of DSSC samples is generally obtained depositing the TiO2 by doctor-blade technique and sealing the electrodes using standard clips, which cannot avoid leakage of electrolyte. This last aspect is probably the most critical one and the assembly procedure does not allow the necessary degree of reproducibility, making hard the comparison of results obtained in different laboratories. Microfluidics is the science and technology of systems that allow manipulating small amounts of fluids, using channels with dimensions in the micrometer scale range [5]. Its advantages lie in the ability to use very small amounts of reagents and to confine and carefully separate different liquids, allowing detection with high sensitivity and low amount of contamination. Moreover, a microfluidic structure can be interfaced with a housing system usually consisting of mechanical clamping, inlet/outlet ports and interconnections to external fluids handling devices [6]. The use of low cost materials and technologies makes it appealing for versatile applications. In fact, the natural application scenario of microfluidics is in microbiology [7], but it has been shown to have a multidisciplinary approach that make it promising in a wide range of research fields, including energy conversion [8]. In this work we report on the first application, to the best of our knowledge, of microfluidic concepts in DSSC fabrication. We designed and fabricated a housing test cell employing a PolyDiMethylSiloxane (PDMS) thin membrane reversibly sealed
A. Lamberti et al. / Microelectronic Engineering 88 (2011) 2308–2310
between the two electrodes with a PolyMethylMethAcrylate (PMMA) clamping system. Sealing performances of such innovative structure were successfully evaluated by dynamic fluidic tests. I–V measurement and impedance spectroscopy characterizations were used to estimate the photovoltaic performance of the cell. 2. Experimental 2.1. Materials and fabrication Fluorine-doped tin oxide (FTO) covered glasses (7 X/sq, Solaronix) were rinsed with acetone and ethanol in an ultrasonic bath for 10 min. Then, a TiO2 layer (Ti-Nanoxide D37 paste, Solaronix) was deposited on FTO by doctor-blade technique and dried at 50 °C for 30 min on a hot plate. A sintering process at 450 °C for 30 min allowed the formation of nanoporous TiO2 film with a mean thickness of 8 lm, as measured by profilometry (P.10 KLA-Tencor Profiler). Photoelectrodes were soaked into a 0.2 mM N719 dye solution (Ruthenizer535bis-TBA, Solaronix) in ethanol for 24 h at room temperature and then rinsed in ethanol to remove the unadsorbed dye. Two small pin-holes for inlet/outlet connections were drilled in the FTO glass counter electrodes through powder blasting technology. Substrates were then cleaned with the same rinsing method described above and a 5 nm Pt thin film was deposited onto FTO by thermal evaporation. Benchman VMC4000 Numerical Control milling machine was used to fabricate the PMMA mechanical clamping with inlet/outlet ports, the masters for the casting of PDMS membrane and O-ring interconnections [9]. PDMS pre-polymer and curing agent (SylgardÒ 184, Dow Corning) were mixed in a 10:1 weight ratio and degassed at room temperature for 1 h. The mixture was then poured into the mould and cured in a convection oven for 1 h at 70 °C. Subsequently, the 200 lm thick membrane was peeled off from the mould and reversibly sandwiched between the electrodes. The electrolyte (Iodolyte AN 50, Solaronix) filling was done with a syringe pump (Syringe-Pump 33, Harvard Apparatus) connected to the housing ports via low density polyethylene (LDPE) tubing. The ports were finally sealed employing homemade caps consisting in LDPE tubes obstructed with PDMS. Additionally, conventional DSSC prototypes were fabricated using the same dye-sensitized photo-electrodes described above and not-drilled FTO glasses. The electrolyte filling was done by soaking up a droplet between the electrodes and the sealing was obtained by clips.
2309
All cells had an active area of 0.36 cm2 and measurements were performed with a 0.16 cm2 mask. 2.2. Characterization setup The fluidic characterization setup consisted on a syringe pump connected, through a ‘T’ joint, to both a commercial pressure transducer (26PCFFA6G Honeywell) and the PDMS interconnection via LDPE tubing. Pressure data vs time were recorded through a multimeter unit (Agilent Technology 34970A) interfaced to a PC. I–V electrical characterizations under AM1.5 illumination (1000 W/m2) were carried out using a class A solar simulator (91195A, Newport) and a Keithley 2440 source measure unit. Electrochemical impedance spectra were collected under illumination using an electrochemical workstation (760D, CH Instruments) in the frequency range 100 mHz 50 kHz, at cell open circuit voltage. 3. Results and discussion The complete housing consisted on mechanical clamping, PDMS interconnection and the operating DSSC with the PDMS membrane reversibly sealed between the two electrodes (Fig. 1). A doubledrop membrane layout was chosen to promote air bubble evacuation during electrolyte filling and a 50 lm retaining ring was designed near the chamber walls to improve the sealing at PDMS/ FTO interfaces. The aid of PDMS press-fit interconnections with the integrated O-ring and the action of the clamping system avoided leakages during the filling step. Sealing performances of the microfluidic architecture were examined by measuring the dynamic pressure endurance at different pressure values and at different temperatures. The handling tests were designed to simulate the in-field employment and the fabrication steps (for example electrolyte filling). Measurements were performed injecting a dye solution at a fixed flow rate (50 ll/min) up to the maximum pressure value (25 and 50 kPa), followed by a 10 min steady state regime obtained stopping the syringe pumping mechanism. The tests were conducted at two different temperatures: 50 and 80 °C. Subsequently, the chamber was reinstated to the initial condition. Experimental results are reported in Fig. 2: chamber pressure profiles vs time showed no temperature dependence for the selected pressures, both during liquid injection and during the steady state regime. It is well known that air bubble inside a micro-structure expands during thermal cycles and could run out of the device through cavities and reversible interfaces [6]. For both pressure values the pla-
Fig. 1. (a) 3D geometry of microfluidic-based DSSC architecture; (b) photograph of fabricated microfluidic-based DSSC.
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A. Lamberti et al. / Microelectronic Engineering 88 (2011) 2308–2310
Fig. 2. Fluidic leakage test of a dye solution at different temperature and pressure values for 10 min.
Representative results for the electrical characterization are shown in Fig. 3. For the microfluidic-based DSSC the photovoltaic parameters were Jsc = 13.94 mA/cm2, Voc = 690 mV, FF = 0.71 and g = 6.4%, evidencing an improved efficiency value compared to the prototype assembled following the standard laboratory procedure (Jsc = 12.39 mA/cm2, Voc = 670 mV, FF = 0.64 and g = 5.1%) with a significant enhancement in short-circuit current. In all the analyzed samples, a mean efficiency increment of the 25% was obtained in microfluidic-based devices. This performances difference between the two kinds of prototypes was additionally evidenced by the impedance spectroscopy analysis. In fact, it is clearly noticeable an improvement in carrier lifetime and a subsequent lower recombination resistance, as illustrated by the second semicircle of the impedance spectra reported in the insert of Fig. 3 [11]. Finally, it is noticeable that microfluidic architecture showed a stable behavior in time: preliminary ageing test conducted on the microfluidic DSSC verified that the efficiency remained unchanged after 3 days. Moreover, no chemical damaging from electrolyte solution was evidenced on PDMS sealing membrane after cell operation. Ageing test over longer times (2 weeks) on microfluidic DSSCs are in progress. 4. Conclusions
Fig. 3. Current density–voltage curves of standard-assembled and microfluidicbased DSSCs; the relative impedance spectra are shown in the insert.
teau-like behavior of the curve was the evidence that no leakages occurred during the test. The independence of the curves from temperature witnessed the absence of air bubble formed in the chamber during liquid charging, as also confirmed by visual check. Thus, no volume expansion occurred, guaranteeing the optimal sealing for in-field operation. During cell fabrication, such microfluidic approach finds its immediate application in electrolyte filling. We demonstrated that this procedure allows a controlled reagent release, since electrolyte can be delivered and removed in the already sealed architecture, avoiding waste and eluding the possible electrode deterioration thanks to a faster assembly process. Moreover, a useful application should also be found in dye sensitization of TiO2. In fact, a more efficient impregnation, avoiding waste of expensive reagents and allowing in situ thermal processes (as suggested by the vendors [10]) can be simply implemented directly on-chip.
An innovative microfluidic housing system for DSSCs has been fabricated and characterization results have been reported. Our new proposed design effectively confines the liquid electrolyte in the final device, improving the lifetime and performance of the prototype by preventing failure due to electrolyte leakage or solvent evaporation. Application of microfluidic concepts in DSSC architecture was also functional to overcome intrinsic problems faced during cell fabrication process. The sealing performance of the housing test cell, fabricated employing a PDMS membrane reversibly sealed between the two transparent electrodes with a PMMA clamping, has been characterized at different pressures and temperatures. Good sealing for pressure up to 50 kPa and temperature of 80 °C has been obtained, avoiding leakage and bubble formation. I–V electrical characterization under illumination and impedance spectroscopy measurement showed a performance improvement with respect to DSSC prototypes fabricated following the standard procedure, of about 25% of the total photovoltaic conversion efficiency. Moreover, the efficiency value remained unchanged after 3 days ageing. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
B. O’Regan, M. Grätzel, Nature 353 (1991) 737–740. Dyesol, web site: www.dyesol.com. M. Grätzel, Inorg. Chem. 44 (2005) 6841–6851. J. Bisquert, D. Cahen, G. Hodes, et al., J. Phys. Chem. B 108 (2004) 8106–8118. G.M. Whitesides, Nature 442 (2006) 368–373. S.L. Marasso, E. Giuri, G. Canavese, et al., Biomed. Microdevices, doi:10.1007/ s10544-010-9467-5. S. Saleh-Lakha, J.T. Trevors, J. Microbiol. Methods 82 (2010) 108–111. S. Pennathur, J.C.T. Eijkel, A. van den Berg, Lab Chip 7 (2007) 1234–1237. M. Quaglio, G. Canavese, E. Giuri, et al., J. Micromech. Microeng. 18 (2008) 1– 10. Solaronix, web site: http://www.solaronix.com/products/dyes. F. Fabregat-Santiago, J. Bisquert, G. Garcia-Belmonteet, et al., Sol. Energy Mat. Sol. Cells 87 (2005) 117–131.
Contents lists available at ScienceDirect
Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee
Microfluidic sealing and housing system for innovative dye-sensitized solar cell architecture A. Lamberti a,b,⇑, A. Sacco a,b, S. Bianco a, E. Giuri b, M. Quaglio a, A. Chiodoni a, E. Tresso b a b
Center for Space Human Robotics, Italian Institute of Technology (IIT), C.so Trento 21, IT-10129 Torino, Italy Materials Science and Chemical Engineering Department, Politecnico di Torino, C.so Duca degli Abruzzi 24, IT-10129 Torino, Italy
a r t i c l e
i n f o
Article history: Received 14 September 2010 Accepted 30 December 2010 Available online 5 January 2011 Keywords: Dye-sensitized solar cells Microfluidics Clamping Housing
a b s t r a c t Dye-sensitized solar cells (DSSCs) have received great attention over the past decade for their high energy conversion efficiency, relatively easy fabrication process and low production cost. However, at present, some practical difficulties such as solvent evaporation, leakage of liquid electrolyte and sealing stability remain serious obstacles to their convenient application. An innovative microfluidic DSSC housing system is here proposed. Sealing performances of such architecture were examined by dynamic fluidic tests and good sealing for pressure up to 50 kPa and temperature of 80 °C was obtained, avoiding leakages and bubble formation. Current–voltage and impedance spectroscopy measurements were used to determine the photovoltaic performance of the cell. Results were compared to the ones obtained with DSSC prototypes assembled in our laboratory following a standard procedure, and higher efficiency values have been obtained. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Solar energy plays a key role in the green economy scenario, and DSSCs have emerged during the last 20 years as one of the most promising approach for a new generation of solar devices [1]. The use of cheap materials and easy fabrication processes and technologies makes them suitable as a low cost solution compared to silicon-based cells, even if they currently show moderate conversion efficiency. In a conventional cell, the photoanode consists of a relatively thick (around 8 lm) layer of TiO2 nanoparticles, electrically interconnected thanks to a sintering process and subsequently sensitized with dye molecules (usually Ru complexes). The TiO2 layer is deposited on a glass slice, covered with transparent conducting oxide (TCO) for electrical contact purposes. A I =I3 redox couple acts as hole conductor, electrically regenerating the dye molecules. The counter electrode consists again on a TCO-covered glass slice with a thin (few nm) layer of Pt, to promote the reduction of the triiodide. Different manufacturing solutions have been proposed for highly performant DSSCs, such as advanced print screen techniques, electrolyte filling and dye profiling machines [2]. As housing for the standard electrochemical cell, the couple of glass slices
⇑ Corresponding author at: Center for Space Human Robotics, Italian Institute of Technology (IIT), C.so Trento 21, IT-10129 Torino, Italy. Tel.: +390110903413. E-mail address: [email protected] (A. Lamberti). 0167-9317/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2010.12.114
are sealed with thermoplastic hot melt glue, creating a free space that is completely filled with electrolyte solution [3,4]. However in research laboratories, where the need is for simple and quick prototypes fabrication, the assembly of DSSC samples is generally obtained depositing the TiO2 by doctor-blade technique and sealing the electrodes using standard clips, which cannot avoid leakage of electrolyte. This last aspect is probably the most critical one and the assembly procedure does not allow the necessary degree of reproducibility, making hard the comparison of results obtained in different laboratories. Microfluidics is the science and technology of systems that allow manipulating small amounts of fluids, using channels with dimensions in the micrometer scale range [5]. Its advantages lie in the ability to use very small amounts of reagents and to confine and carefully separate different liquids, allowing detection with high sensitivity and low amount of contamination. Moreover, a microfluidic structure can be interfaced with a housing system usually consisting of mechanical clamping, inlet/outlet ports and interconnections to external fluids handling devices [6]. The use of low cost materials and technologies makes it appealing for versatile applications. In fact, the natural application scenario of microfluidics is in microbiology [7], but it has been shown to have a multidisciplinary approach that make it promising in a wide range of research fields, including energy conversion [8]. In this work we report on the first application, to the best of our knowledge, of microfluidic concepts in DSSC fabrication. We designed and fabricated a housing test cell employing a PolyDiMethylSiloxane (PDMS) thin membrane reversibly sealed
A. Lamberti et al. / Microelectronic Engineering 88 (2011) 2308–2310
between the two electrodes with a PolyMethylMethAcrylate (PMMA) clamping system. Sealing performances of such innovative structure were successfully evaluated by dynamic fluidic tests. I–V measurement and impedance spectroscopy characterizations were used to estimate the photovoltaic performance of the cell. 2. Experimental 2.1. Materials and fabrication Fluorine-doped tin oxide (FTO) covered glasses (7 X/sq, Solaronix) were rinsed with acetone and ethanol in an ultrasonic bath for 10 min. Then, a TiO2 layer (Ti-Nanoxide D37 paste, Solaronix) was deposited on FTO by doctor-blade technique and dried at 50 °C for 30 min on a hot plate. A sintering process at 450 °C for 30 min allowed the formation of nanoporous TiO2 film with a mean thickness of 8 lm, as measured by profilometry (P.10 KLA-Tencor Profiler). Photoelectrodes were soaked into a 0.2 mM N719 dye solution (Ruthenizer535bis-TBA, Solaronix) in ethanol for 24 h at room temperature and then rinsed in ethanol to remove the unadsorbed dye. Two small pin-holes for inlet/outlet connections were drilled in the FTO glass counter electrodes through powder blasting technology. Substrates were then cleaned with the same rinsing method described above and a 5 nm Pt thin film was deposited onto FTO by thermal evaporation. Benchman VMC4000 Numerical Control milling machine was used to fabricate the PMMA mechanical clamping with inlet/outlet ports, the masters for the casting of PDMS membrane and O-ring interconnections [9]. PDMS pre-polymer and curing agent (SylgardÒ 184, Dow Corning) were mixed in a 10:1 weight ratio and degassed at room temperature for 1 h. The mixture was then poured into the mould and cured in a convection oven for 1 h at 70 °C. Subsequently, the 200 lm thick membrane was peeled off from the mould and reversibly sandwiched between the electrodes. The electrolyte (Iodolyte AN 50, Solaronix) filling was done with a syringe pump (Syringe-Pump 33, Harvard Apparatus) connected to the housing ports via low density polyethylene (LDPE) tubing. The ports were finally sealed employing homemade caps consisting in LDPE tubes obstructed with PDMS. Additionally, conventional DSSC prototypes were fabricated using the same dye-sensitized photo-electrodes described above and not-drilled FTO glasses. The electrolyte filling was done by soaking up a droplet between the electrodes and the sealing was obtained by clips.
2309
All cells had an active area of 0.36 cm2 and measurements were performed with a 0.16 cm2 mask. 2.2. Characterization setup The fluidic characterization setup consisted on a syringe pump connected, through a ‘T’ joint, to both a commercial pressure transducer (26PCFFA6G Honeywell) and the PDMS interconnection via LDPE tubing. Pressure data vs time were recorded through a multimeter unit (Agilent Technology 34970A) interfaced to a PC. I–V electrical characterizations under AM1.5 illumination (1000 W/m2) were carried out using a class A solar simulator (91195A, Newport) and a Keithley 2440 source measure unit. Electrochemical impedance spectra were collected under illumination using an electrochemical workstation (760D, CH Instruments) in the frequency range 100 mHz 50 kHz, at cell open circuit voltage. 3. Results and discussion The complete housing consisted on mechanical clamping, PDMS interconnection and the operating DSSC with the PDMS membrane reversibly sealed between the two electrodes (Fig. 1). A doubledrop membrane layout was chosen to promote air bubble evacuation during electrolyte filling and a 50 lm retaining ring was designed near the chamber walls to improve the sealing at PDMS/ FTO interfaces. The aid of PDMS press-fit interconnections with the integrated O-ring and the action of the clamping system avoided leakages during the filling step. Sealing performances of the microfluidic architecture were examined by measuring the dynamic pressure endurance at different pressure values and at different temperatures. The handling tests were designed to simulate the in-field employment and the fabrication steps (for example electrolyte filling). Measurements were performed injecting a dye solution at a fixed flow rate (50 ll/min) up to the maximum pressure value (25 and 50 kPa), followed by a 10 min steady state regime obtained stopping the syringe pumping mechanism. The tests were conducted at two different temperatures: 50 and 80 °C. Subsequently, the chamber was reinstated to the initial condition. Experimental results are reported in Fig. 2: chamber pressure profiles vs time showed no temperature dependence for the selected pressures, both during liquid injection and during the steady state regime. It is well known that air bubble inside a micro-structure expands during thermal cycles and could run out of the device through cavities and reversible interfaces [6]. For both pressure values the pla-
Fig. 1. (a) 3D geometry of microfluidic-based DSSC architecture; (b) photograph of fabricated microfluidic-based DSSC.
2310
A. Lamberti et al. / Microelectronic Engineering 88 (2011) 2308–2310
Fig. 2. Fluidic leakage test of a dye solution at different temperature and pressure values for 10 min.
Representative results for the electrical characterization are shown in Fig. 3. For the microfluidic-based DSSC the photovoltaic parameters were Jsc = 13.94 mA/cm2, Voc = 690 mV, FF = 0.71 and g = 6.4%, evidencing an improved efficiency value compared to the prototype assembled following the standard laboratory procedure (Jsc = 12.39 mA/cm2, Voc = 670 mV, FF = 0.64 and g = 5.1%) with a significant enhancement in short-circuit current. In all the analyzed samples, a mean efficiency increment of the 25% was obtained in microfluidic-based devices. This performances difference between the two kinds of prototypes was additionally evidenced by the impedance spectroscopy analysis. In fact, it is clearly noticeable an improvement in carrier lifetime and a subsequent lower recombination resistance, as illustrated by the second semicircle of the impedance spectra reported in the insert of Fig. 3 [11]. Finally, it is noticeable that microfluidic architecture showed a stable behavior in time: preliminary ageing test conducted on the microfluidic DSSC verified that the efficiency remained unchanged after 3 days. Moreover, no chemical damaging from electrolyte solution was evidenced on PDMS sealing membrane after cell operation. Ageing test over longer times (2 weeks) on microfluidic DSSCs are in progress. 4. Conclusions
Fig. 3. Current density–voltage curves of standard-assembled and microfluidicbased DSSCs; the relative impedance spectra are shown in the insert.
teau-like behavior of the curve was the evidence that no leakages occurred during the test. The independence of the curves from temperature witnessed the absence of air bubble formed in the chamber during liquid charging, as also confirmed by visual check. Thus, no volume expansion occurred, guaranteeing the optimal sealing for in-field operation. During cell fabrication, such microfluidic approach finds its immediate application in electrolyte filling. We demonstrated that this procedure allows a controlled reagent release, since electrolyte can be delivered and removed in the already sealed architecture, avoiding waste and eluding the possible electrode deterioration thanks to a faster assembly process. Moreover, a useful application should also be found in dye sensitization of TiO2. In fact, a more efficient impregnation, avoiding waste of expensive reagents and allowing in situ thermal processes (as suggested by the vendors [10]) can be simply implemented directly on-chip.
An innovative microfluidic housing system for DSSCs has been fabricated and characterization results have been reported. Our new proposed design effectively confines the liquid electrolyte in the final device, improving the lifetime and performance of the prototype by preventing failure due to electrolyte leakage or solvent evaporation. Application of microfluidic concepts in DSSC architecture was also functional to overcome intrinsic problems faced during cell fabrication process. The sealing performance of the housing test cell, fabricated employing a PDMS membrane reversibly sealed between the two transparent electrodes with a PMMA clamping, has been characterized at different pressures and temperatures. Good sealing for pressure up to 50 kPa and temperature of 80 °C has been obtained, avoiding leakage and bubble formation. I–V electrical characterization under illumination and impedance spectroscopy measurement showed a performance improvement with respect to DSSC prototypes fabricated following the standard procedure, of about 25% of the total photovoltaic conversion efficiency. Moreover, the efficiency value remained unchanged after 3 days ageing. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
B. O’Regan, M. Grätzel, Nature 353 (1991) 737–740. Dyesol, web site: www.dyesol.com. M. Grätzel, Inorg. Chem. 44 (2005) 6841–6851. J. Bisquert, D. Cahen, G. Hodes, et al., J. Phys. Chem. B 108 (2004) 8106–8118. G.M. Whitesides, Nature 442 (2006) 368–373. S.L. Marasso, E. Giuri, G. Canavese, et al., Biomed. Microdevices, doi:10.1007/ s10544-010-9467-5. S. Saleh-Lakha, J.T. Trevors, J. Microbiol. Methods 82 (2010) 108–111. S. Pennathur, J.C.T. Eijkel, A. van den Berg, Lab Chip 7 (2007) 1234–1237. M. Quaglio, G. Canavese, E. Giuri, et al., J. Micromech. Microeng. 18 (2008) 1– 10. Solaronix, web site: http://www.solaronix.com/products/dyes. F. Fabregat-Santiago, J. Bisquert, G. Garcia-Belmonteet, et al., Sol. Energy Mat. Sol. Cells 87 (2005) 117–131.