Cost effective natural photo sensitizer from upcycled jackfruit rags for dye sensitized solar cells

Journal of Science: Advanced Materials and Devices (2018) 213e220 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Cost effective natural photo-sensitizer from upcycled jackfruit rags for dye sensitized solar cells Aditya Ashok, Sumi E Mathew, Shivakumar B Shivaram, Sahadev A Shankarappa, Shantikumar V Nair, Mariyappan Shanmugam* Amrita Center for Nanosciences and Molecular Medicine, Amrita Vishwa Vidyapeetham, Kerala 682041, India a r t i c l e i n f o a b s t r a c t Article history: Received February 2018 Received in revised form 15 April 2018 Accepted 19 April 2018 Available online 27 April 2018 Photo-sensitizers, usually organic dye molecules, are considered to be one of the most expensive components in dye sensitized solar cells (DSSCs) The present work demonstrates a cost effective and high throughput upcycling process on jackfruit rags to extract a natural photo-active dye and its application as a photo-sensitizing candidate on titanium dioxide (TiO2) in DSSCs The jackfruit derived natural dye (JDND) exhibits a dominant photo-absorption in a spectral range of 350 nme800 nm with an optical bandgap of ~1.1 eV estimated from UVevisible absorption spectroscopic studies The JDND in DSSCs as a major photo-absorbing candidate exhibits a photo-conversion efficiency of ~1.1% with short circuit current density and open circuit voltage of 2.2 mA,cmÀ2 and 805 mV, respectively Further, the results show that the concentration of JDND plays an influential role on the photovoltaic performance of the DSSCs due to the significant change in photo-absorption, exciton generation and electron injection into TiO2 The simple, high throughput method used to obtain JDND and the resulting DSSC performance can be considered as potential merits establishing a cost effective excitonic photovoltaic technology © 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: Solar cell Dyes Titanium dioxide Photo-absorption Charge transport Introduction Requirement of cost effective and high performance energy harvesting technologies to meet the future energy demand urges researchers to explore multifarious functional materials for solar cell applications [1e3] Dye sensitized solar cells (DSSCs) have been realized as potential alternate for many bulk and thin film based third generation photovoltaics due to the usage of low cost materials and simple fabrication processes [4e7] While silicon and other thin film based solar cell fabrication demands high vacuum and high temperature processing in controlled environments, DSSCs are fabricated via non-vacuum deposition techniques showing competitive photo-conversion efficiencies (h) [8,9] Various functional materials such as fluorine doped tin oxide (FTO), titanium dioxide (TiO2), photo-absorbing dyes, hole transporting electrolytes and counter electrodes are still under research for further development of hybrid photovoltaic technology [10] Photosensitizing organic dyes are important and influential components * Corresponding author E-mail address: mshanmugham@aims.amrita.edu (M Shanmugam) Peer review under responsibility of Vietnam National University, Hanoi in DSSCs to determine the overall photovoltaic performance Ruthenium, porphyrin and phthalocyanine based organic dyes have shown promising h values in DSSCs [11e13] Photo-sensitizing dyes play a critical role in DSSC performance in terms of light absorption, exciton generation, and electron injection into electron acceptors which determine short circuit current density (JSC) and thus h in DSSCs [14] While ruthenium and porphyrin based dyes show an exceptional photovoltaic performance in DSSCs, various other routes have recently been explored to extract natural dyes [15e17] Sathyajothi et al has recently reported that extracts from beetroot and henna have shown promising photo-absorption in the visible spectrum and thus yielded DSSCs with 1.3% and 1.08% efficiency, respectively [18] Natural dyes are relatively low cost materials due to the simple straightforward processing to extract the dyes from sources such as flowers and fruits [19,20] Natural dyes obtained from flowers, such as rose, lily and fruits, such as Fructus lycii have shown potential merits of considering natural resources to develop cost effective energy harvesting technologies [19] Albei natural dye extracts have generally shown relatively lower DSSC performance compared to ruthenium and porphyrin based dyes, but, in contrast, recently coumarin based natural dyes have shown h of 7.6% [21] It shows the possibility of developing high performance DSSCs via modified https://doi.org/10.1016/j.jsamd.2018.04.006 2468-2179/© 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) 214 A Ashok et al / Journal of Science: Advanced Materials and Devices (2018) 213e220 natural dyes It is important to note that the pigments contained in the natural dyes are the sources to determine the active photoabsorption spectral window The present research scenario points out the possibility of developing low cost photo-sensitizers from natural resources while the performance of the resulting solar cells is relatively lower In general, the energy level alignment between the TiO2 and lowest unoccupied molecular orbital (LUMO) of the dye determines the efficient electron injection while the alignment between the highest occupied molecular orbital (HOMO) of the dye and the redox potential of the electrolyte influences the regeneration of the dye molecules These two factors primarily stipulate the electron and hole transport in DSSCs Additionally, the energy gap between HOMO and LUMO of the natural extract is an essential parameter which determines the spectral energy range in which the dye absorbs photons and this directly controls JSC of the resulting DSSCs Design and development of novel photo-sensitizers for DSSCs are expected to lead to a successful establishment of cost effective photovoltaics The present work examines a natural dye that has been derived from jackfruit rags, a least used and discarded component from jackfruits, and its application as a major photo-sensitizer in DSSCs It is an attempt to establish a simple, cost effective and high throughput natural dye development process via upcycling the jackfruit waste for DSSC applications supernatant was ml The supernatant was further processed using a centrifugal concentrator at 1725 rpm for 16 h at 35  C The resulting extract had a thick viscous consistency, devoid of methanol as a stock dye solution The stock dye solution was further diluted to obtain the required concentrations for the study of the effect on photo-absorption This method yielded 1.5 g powder Fig shows schematic of the process flow followed in the upcycling process of jackfruit rags into dye and their use in preparation of photo-anodes for DSSCs 2.2 Fabrication of DSSCs with JDND Experimental A stock dye solution of JDND was prepared as explained in the previous section and stock solutions with three different concentrations (10, 20 and 30 mg) of JDND were prepared A colloidal nanoparticle TiO2 layer was prepared using commercially available anatase TiO2 nanoparticles by the doctor blade method The JDND dyes with the three different concentration values were used to sensitize the TiO2 Commercially available Iodolyte AN-50 was used as a hole transporting layer A 50 nm thin Pt film was used as a counter electrode The JDND coated TiO2 photo-anodes and the Pt coated counter electrodes were coupled and the electrolyte was injected between the two electrodes through a pre-made channel on a parafilm spacer used to couple the electrodes Further, this study was performed using cobalt as an alternate electrolyte to check the compatibility of JDND with cobalt redox couple No TiCl4 treatment and TiO2 blocking layer were used in this work 2.1 Process of upcycling the jackfruit rags and dye synthesis 2.3 Materials and solar cell characterizations Commercially available jackfruits were obtained and the fruits were cut, openned to separate the waste rags as a source material for the dye preparation The separated rags were powdered and were suspended in 80% acidified (1.2 M HCl) methanol as a solvent at a concentration of 10% w/v The mixture was heated at 50  C for h and then 100% methanol in a volume ratio of 1:2 was added A supernatant was collected from the solution by centrifuging at 1000 rpm for at  C after removing the solid fraction The original volume of the material was 10 ml and the volume of Morphology of the jackfruit rags and colloidal TiO2 nanoparticles containing samples were characterized in a scanning electron microscope (SEM) using the JEOL-JSM-6490-LA Energy dispersive X-ray (EDX) analysis was performed with an accelerating voltage of 15 kV in the range of 0e10 keV The jackfruit rags were prepared for SEM using 2% glutaraldehyde and subjected to dehydration by graded aqueous solutions of glycerol (80e100%) for h The rags were then cut into circumferential and longitudinal sections to obtain surface and cross-sectional views in SEM Optical Fig Schematic illustration of the process flow involved in the extraction of the photo-sensitizing dye from jackfruit rags using methanol as a solvent A Ashok et al / Journal of Science: Advanced Materials and Devices (2018) 213e220 characteristics of the JDND and TiO2 were studied by Perkin Elmer Lambda-750 UVevisible spectrometer The current densityevoltage (JeV) measurements of the DSSCs were performed under AM1.5 illumination level using a solar simulator (Newport Oriel Class A) and a digital source meter (Keithley 2400) Electrochemical impedance spectroscopic measurements were performed on the fabricated DSSCs in the Autolab electrochemical workstation under dark condition Results and discussion Fig shows the photographic images of (a) the stock dye solution extracted from the waste rags in jackfruit The jackfruit rags are well known waste material and this study explores the possibility of upcycling the waste portion for the energy harvesting application by extracting the photo-sensitizer shown in Fig 2(a) The pristine dye extracted from the rags was observed to be dark reddish-brown and this study selected three different concentration values for DSSC applications by diluting the stock solution From the original stock solution shown in Fig 2(a), 10 mg, 20 mg and 30 mg of the dye was separated and used to sensitize the colloidal TiO2 films for DSSCs and the three diluted concentrations of JDND are shown in Fig 2(b) The images (i), (ii) and (iii) in Fig 2(b) show the 10 mg, 20 mg and 30 mg, respectively The three solutions with diluted concentrations were used to sensitize the colloidal TiO2 layers and the respective fabricated photo-anodes are shown in Fig 2(c): ieiv The digital images show that the JDND diffused into the TiO2 layer and the variation in concentration can also be asserted from the photographs shown Fig shows the SEM images obtained from the surface of the jackfruit rags (a) and from the cross-sectional views from the rags (b) and (c) obtained by breaking them across The rags were observed like smooth fibrous stacks as shown in Fig 3(a) The crosssectional views of the as fresh collected rags and those cleaned with DI-water cleaned are shown in Fig 3(b) and (c), respectively The cross-sectional SEM images elucidate that the rags look like hollow fibers and they look better after the DI water cleaning Fig 3(b) and (c) show the hollow fibers as bundles in the rags and these are 215 randomly arranged It is noticed that each hollow fiber in the bundle of rags is well separated by thin walls and the arrangement is few micron in size Some of the regions are observed to have damaged hollow fibrous bundles and that are due to the manual cutting to acquire the cross-sectional images Fig 3(d) shows the surface morphology of the TiO2 nanoparticle layer used as an electron acceptor in the DSSCs presented in this work This layer appears highly porous and the nanoparticles are randomly distributed as can be viewed in the agglomerated microscopic clusters formed by the TiO2 nanoparticles The agglomerated nanoparticles as clusters in the surface are well connected to each other through which electron transport is established in the resulting DSSCs Thus, the SEM surface morphology images reveal the presented material to be highly suitable for DSSC as an electron acceptor Fig shows UVevis optical absorption spectra taken on the JDND and the colloidal TiO2 nanoparticles on which the dye molecules were coated Optical absorbance data of the three samples with different JDND concentrations (JDND1-10 mg, JDND2-20 mg and JDND3-30 mg) are shown in Fig 4(a) It is expected that absorbance will increase as the JDND concentration increases As can be seen, JDND3 exhibits a stronger absorbance in the whole wavelength range of 350 nme1000 nm and it is only due to the increased concentration The wavelength range in which the dye is actively absorbing photons is the same for all three samples and the change in the quantity of absorbance corresponds to the change in the JDND concentration The dominant absorbance characteristics of the three samples in the spectral range up to 1000 nm are further confirmed by the corresponding transmittance behavior in the same spectral window as shown in Fig 4(b) As they show decreased optical absorbance starting around 700 nm, the transmittance increases at 700 nm which is in good agreement with their corresponding absorbance characteristics shown in Fig 4(a) The present study explores the photo-absorbance ability of JDND and the application in DSSCs Thus, it is important to compare the optical properties of JDND with those of TiO2 as they both make the photo-anodes for resulting DSSCs Fig 4(c) shows a comparison of the optical absorbance characteristics of JDND with TiO2 Fig Photographs of the (a) stock JDND dye solution extracted from the rags (b) three solutions with respective concentrations prepared as illustrated in (i)e(iii) (c) Photo-anode preparation for DSSCs showing (i) pure TiO2 anatase nanoparticle layer on FTO and TiO2 sensitized with three different concentrations of JDND dye (ii)e(iv) 216 A Ashok et al / Journal of Science: Advanced Materials and Devices (2018) 213e220 Fig SEM images showing (a) the surface topography of the jackfruit rags (b) and (c) cross-sectional views obtained from the rags after breaking them across (d) Surface morphology of the TiO2 nanoparticle layer used as an electron acceptor in DSSCs Fig (a) UVevis optical absorbance (b) Transmittance characteristics for three different JDND concentration values (c) Comparison of the absorbance between JDND and TiO2 with an inset showing the corresponding transmittance characteristics (d) Optical bandgap values of JDND and TiO2 in comparison A Ashok et al / Journal of Science: Advanced Materials and Devices (2018) 213e220 nanoparticles used as an electron acceptor in which the JDND was coated as a photo-sensitizer It is shown in Fig 4(c) that the optical absorbance of TiO2 in the spectral window of 350 nme1000 nm is negligible while the absorbance of JDND is dominant It is a major requirement for an electron acceptor and photo-sensitizing dye to have the optical compatibility in a particular spectral window in which the dye should exhibit a dominant absorbance while the electron acceptor shows a negligible one Thus, the dye can generate excitons and inject electrons into the conduction band of the electron acceptor and the later transports the photo-generated electrons to the electrode via a diffusive transport process Further, absorption coefficient values (a in cmÀ1) of JDND and TiO2 were calculated and Tauc plot was made to extract the values of the optical bandgap and the results are shown in Fig 4(d) TiO2 shows the 3.1 eV optical bandgap while the JDND exhibits 1.1 eV and these values are in line with the optical absorbance characteristic spectra shown in Fig 4(c) for JDND and TiO2 Fig shows the EDX analysis carried out on the JDND sample to examine the constituents with respect to their energy dependency Fig 5(a) shows the surface morphology in which the EDX scan was 217 performed and (b)-(f) show the distribution of the major constituents carbon, oxygen, sodium, chlorine and potassium, respectively Further all the elements were confirmed with respect to their energies as shown in Fig 5(g) along with the quantification to estimate their mass and atomic % as shown in the inset table Fig (a) shows the JeV characteristics of the DSSCs utilizing JDND as a photo-sensitizer on the TiO2 nanoparticle layer Three different concentrations of JDND (JDND1: 10 mg, JDND2: 20 mg, JDND3: 30 mg) of the dye were utilized to in the DSSCs In this study, the iodide electrolyte was used as a hole transport material in the DSSCs The photovoltaic performance metrics of the three DSSCs measured under the AM1.5 illumination level are listed in Table The DSSC utilized JDND2 as a photo-sensitizer (20 mg) yielded values of JSC, VOC, FF and h in the order of 2.2 mA cmÀ2, 805 mV, 60.4%, and 1.1%, respectively In general, photonic absorption of concentrated material will dominate those of materials with lower concentrations as it was shown in the UVevis optical absorption studies presented already in Fig 4(a) However, the JeV characteristics of the DSSC utilizing the concentration of 30 mg of JDND yielde a JSC value, which is 47% less than that Fig (a) The JDND surface on which the EDX was performed to show (b) carbon, (c) oxygen, (d) sodium, (e) chlorine and (f) potassium (g) The energy distribution spectrum with an inset showing the mass and atomic % of all constituents in the JDND 218 A Ashok et al / Journal of Science: Advanced Materials and Devices (2018) 213e220 Fig (a) JeV characteristics of the DSSCs with the iodide electrolyte showing the performance variation with respect to the concentration of JDND used to sensitize the TiO2, EIS studies performed on the DSSCs showing (b) Nyquist and (c) Bode phase characteristics Table Photovoltaic parameters measured under AM1.5 illumination condition Photo-sensitizer JSC (mA/cm2) VOC (mV) FF (%) h (%) JDND1 JDND2 JDND3 1.24 2.21 1.50 824 805 824 63.83 60.37 59.95 0.65 1.07 0.74 obtained with the DSSC utilizing 20 mg of JDND This can be attributed as due to the interface between TiO2/JDND We believe that higher JDND concentration contributes to generating more excitons but it forms agglomeration on the surface of TiO2 nanoparticles JDND1 (10 mg) in DSSC yielded a value of 1.2 mA cmÀ2 for JSC, which is lower than those obtained for the other two DSSCs with JDND2 and JDND3, meaning the relatively lower concentration of JDND in DSSCs has resulted in a low photo-absorption While the concentration of photo-sensitizer increased from 10 mg to 20 mg in the photo-anode, JSC increased to 78% However, the further increase in JDND concentration, from 20 mg to 30 mg, does not follow the same trend as observed in the JeV characteristics of the DSSCs It is explicit that there is an optimum JDND concentration to provide an uniform surface coverage on the TiO2 nanoparticle layer and that is correlated to an optimum JSC value and thus can lead to a maximum possible photovoltaic performance As it can be seen, all three DSSCs yieded better VOC values (~805 mVe824 mV) with decent values of FF (60%e64%) Here, JSC is considred the only factor which controlled the overall performance of the reported DSSCs The upcycling process to extract the natural dye from the jackfruit rags is a highly optimized lab-scale experimental procedure but the extracted dye used in this study was not further purified by any procedures The present work presents only the application of a waste material in energy harvesting technology without having any further modification In general, the synthesis of various dye molecules accounts multi-step rigorous procedures with purification steps As a result, the use of such purified dyes in DSSCs commonly can ensure high performance As prepared pristine JDND reported in the present work accounts no modifications in the dye in terms of purification and A Ashok et al / Journal of Science: Advanced Materials and Devices (2018) 213e220 doping Thus, the lower JSC values are the direct representation of the pristine JDND and might be the limitation of the upcycled jackfruit rags Fig 5(b) and (c) show Nyquist and Bode phase characteristics of the DSSCs utilizing JDND with different concentrations The charge transfer and recombination resistive characteristics in the DSSCs can be realized from the Nyquist and Bode phase plots shown in Fig 6(b) and (c), respectively The size of the semi-circles obtained from the three DSSCs shows that the resistance to the recombination increased which significantly facilitates the charge transfer process at TiO2/JDND/electrolyte interfaces It is well known that interfacial kinetics at the electron acceptor/hole transport material is the dominant factor that determines the charge transfer and recombination processes in the DSSCs Bode phase plots shown in Fig 6(c) look similar in cases of DSSCs utilizing JDND2 and JDND3 This is in good agreement with their performance shown in Fig 6(a) Further, the compatibility of JDND with other electrolytes, for example cobalt, was examined in DSSCs utilizing cobalt as a hole transport layer Fig 7(a) shows the JeV characteristic of the DSSC with cobalt as a hole transport layer and JDND2 as a photosensitizer As the results show, the cobalt electrolyte can also yield 219 higher VOC but lower JSC values than that of DSSCs using iodide as a hole transport material The DSSC with cobalt electrolyte yield values of JSC, VOC, FF and h in the order of 0.4 mA cmÀ2, 783 mV, 60.5% and 0.3%, respectively Fig 7(b) and (c) show the Nyquist and Bode phase characteristics of the JDND based DSSCs with cobalt electrolyte The smaller semi-circle obtained from this DSSC compared to those of the DSSCs with iodide electrolyte and the maximum phase angle at a higher frequency assert that the charge transfer and the recombination resistances are affected which directly demonstrates that the interfacial charge transport kinetics are better at TiO2/JDND/ iodide interface than that of in TiO2/JDND/cobalt The two hole transport materials examined in the present work (iodine and cobalt based) are well known in the excitonic photovoltaic technology The JDND extracted from the rags of jackfruit waste shows decent JSC and higher VOC values with two important commercial available electrolytes confirming optimum band alignment (HOMO with redox potentials of the electrolytes and LUMO with conduction band of TiO2) and thus it can lead to large scale production for commercialization at lower cost Table summarizes few important natural dye sources and their application in DSSCs with maximum reported h values Fig (a) JeV characteristic of the DSSCs with cobalt electrolyte, EIS studies performed on the DSSCs show the (b) Nyquist and (c) Bode phase characteristics 220 A Ashok et al / Journal of Science: Advanced Materials and Devices (2018) 213e220 Table Photovoltaic performance of well-known natural dyes reported Dye source h (%) Reference Begoniaa Mangosteen pericarp Rose Shisonin Henna Beetroot Jackfruit rags 0.24 1.17 0.38 1.01 1.08 1.30 1.07 [15] [15] [15] [17] [18] [18] This study In general, all natural resources extracted dyes exhibit low photovoltaic performance However, photovoltaic research, as a green energy technology, prefers low cost natural materials to develop environmental friendly functional materials for viable DSSC applications Mangosteen pericarp and Shisonin have been reported to yield values of h of slightly greater than 1% while other sources give lower h than the two aboved mentioned [15] The JDND reported in the present work is pristine without any further purification process Thus, we believe the JSC and the overall performance of the DSSC can be further improved if chemical purification steps can be adopted However, JDND, as a waste derived photo-sensitizer, has shown comparable performance as confirmed by the photo-absorption of the material and the performance of the resulting DSSCs Various natural sources reported so far are usable materials in various forms including food and cosmetics The present study demonstrates the possibility of upcycling the waste portion from jackfruits and possible application in DSSCs as a photo-sensitizing candidate As the waste portion from the jackfruit is considered as a source for the synthesis of photosensitizer reported in this work, it is expected to be cost effective to make the resulting photovoltaic technology viable and affordable The well-known photo-sensitizers N719 and Z907 are commercially available in the price range of USD 300eUSD 450 for a quantity of 500 mg The performance obtained from the JDND in DSSCs is comparable with the reports claiming other natural materials The illuminated photovoltaic parameters obtained from the DSSCs utilized JDND as a photo-sensitizer such as JSC, VOC and FF are much higher than the other dyes extracted from the natural resources reported [15] Further, the jackfruit grows in the humid and hot tropics without having much issues This is an additional advantage for the availability of the waste source material to prepare the photo-sensitizer The locally available waste as a source material is expected to reduces the material production cost which will eventually help energy harvesting at low cost Thus, the simple upcycling process of jackfruit rags to achieve photo-sensitizer for DSSCs can be considered as a potential material synthesis platform for cost effective photovoltaics Conclusion A simple high throughput process has been demonstrated to upcycle jackfruit rags to derive natural photoactive dye for energy harvesting application The significant photo-absorption in the visible spectral range confirms that JDND can be considered as a cost effective photo-sensitizer as it is derived from jackfruit rags The DSSCs employed the JDND showed promising photovoltaic performance leading to the development of low cost photosensitizers for energy harvesting applications Acknowledgements We thank Department of Science and Technology, Government of India for financial support through Solar Energy Research Initiative and Department of Biotechnology, India for the Ramalingaswamy fellowship grant References [1] B Parida, S Iniyan, R Goic, A review of solar photovoltaic technologies, Renew Sustain Energy 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