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

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[r]

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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,

Amrita Center for Nanosciences and Molecular Medicine, Amrita Vishwa Vidyapeetham, Kerala 682041, India

a r t i c l e i n f o

Article history:

Received 9 February 2018

Received in revised form

15 April 2018

Accepted 19 April 2018

Available online 27 April 2018

Keywords:

Solar cell

Dyes

Titanium dioxide

Photo-absorption

Charge transport

a b s t r a c t

Photo-sensitizers, usually organic dye molecules, are considered to be one of the most expensive com-ponents 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,cm 2and 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/)

1 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 thinﬁlm based

third generation photovoltaics due to the usage of low cost

mate-rials and simple fabrication processes [4e7] While silicon and

other thinﬁlm 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 asﬂuorine 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]

Photo-sensitizing organic dyes are important and inﬂuential components

in DSSCs to determine the overall photovoltaic performance Ruthenium, porphyrin and phthalocyanine based organic dyes have shown promisinghvalues in DSSCs[11e13]

Photo-sensitizing dyes play a critical role in DSSC performance

in terms of light absorption, exciton generation, and electron in-jection into electron acceptors which determine short circuit cur-rent density (JSC) and thushin DSSCs[14] While ruthenium and porphyrin based dyes show an exceptional photovoltaic perfor-mance in DSSCs, various other routes have recently been explored

to extract natural dyes[15e17] Sathyajothi et al has recently re-ported that extracts from beetroot and henna have shown prom-ising 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 shownhof 7.6%[21] It shows the possibility of developing high performance DSSCs via modiﬁed

* Corresponding author.

E-mail address: mshanmugham@aims.amrita.edu (M Shanmugam).

Peer review under responsibility of Vietnam National University, Hanoi.

Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d

https://doi.org/10.1016/j.jsamd.2018.04.006

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natural dyes It is important to note that the pigments contained in

the natural dyes are the sources to determine the active

photo-absorption 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

ab-sorbs photons and this directly controls JSCof 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

2 Experimental

2.1 Process of upcycling the jackfruit rags and dye synthesis

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 50C for

5 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 5 min at 4C after removing the solid fraction The

original volume of the material was 10 ml and the volume of

supernatant was 3 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 meth-anol 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 1 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

A stock dye solution of JDND was prepared as explained in the previous section and stock solutions with three different concen-trations (10, 20 and 30 mg) of JDND were prepared A colloidal nanoparticle TiO2layer was prepared using commercially available anatase TiO2nanoparticles 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 Ptﬁlm was used as a counter electrode The JDND coated TiO2photo-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 TiO2blocking layer were used in this work 2.3 Materials and solar cell characterizations

Morphology of the jackfruit rags and colloidal TiO2 nano-particles 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 dehy-dration by graded aqueous solutions of glycerol (80e100%) for 1 h The rags were then cut into circumferential and longitudinal sec-tions to obtain surface and cross-sectional views in SEM Optical

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 3 (2018) 213e220 214

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characteristics of the JDND and TiO2were 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)

Electro-chemical impedance spectroscopic measurements were performed

on the fabricated DSSCs in the Autolab electrochemical workstation

under dark condition

3 Results and discussion

Fig 2shows the photographic images of (a) the stock dye

so-lution extracted from the waste rags in jackfruit The jackfruit rags

are well known waste material and this study explores the

possi-bility of upcycling the waste portion for the energy harvesting

application by extracting the photo-sensitizer shown inFig 2(a)

The pristine dye extracted from the rags was observed to be dark

reddish-brown and this study selected three different

concentra-tion values for DSSC applicaconcentra-tions by diluting the stock soluconcentra-tion

From the original stock solution shown inFig 2(a), 10 mg, 20 mg

and 30 mg of the dye was separated and used to sensitize the

colloidal TiO2ﬁlms 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 TiO2layers and the respective fabricated photo-anodes are

shown inFig 2(c): ieiv The digital images show that the JDND

diffused into the TiO2layer and the variation in concentration can

also be asserted from the photographs shown

Fig 3shows 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 smoothﬁbrous stacks as shown inFig 3(a) The

cross-sectional views of the as fresh collected rags and those cleaned with

DI-water cleaned are shown inFig 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 hollowﬁbers as bundles in the rags and these are

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 hollowﬁbrous 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 4 shows UVevis optical absorption spectra taken on the JDND and the colloidal TiO2nanoparticles on which the dye mol-ecules 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 trans-mittance increases at 700 nm which is in good agreement with their corresponding absorbance characteristics shown inFig 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 TiO2as 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 2 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

sensitized with three different concentrations of JDND dye (ii)e(iv).

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Fig 3 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 TiO 2 nanoparticle layer used as an electron acceptor in DSSCs.

Fig 4 (a) UVevis optical absorbance (b) Transmittance characteristics for three different JDND concentration values (c) Comparison of the absorbance between JDND and TiO 2

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nanoparticles used as an electron acceptor in which the JDND was

coated as a photo-sensitizer It is shown inFig 4(c) that the optical

absorbance of TiO2in 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 (ain cm 1) of JDND and TiO2were

calculated and Tauc plot was made to extract the values of the

optical bandgap and the results are shown inFig 4(d) TiO2shows

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 inFig 4(c) for JDND and TiO2

Fig 5shows 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

performed and (b)-(f) show the distribution of the major constit-uents carbon, oxygen, sodium, chlorine and potassium, respec-tively Further all the elements were conﬁrmed with respect to their energies as shown inFig 5(g) along with the quantiﬁcation to es-timate their mass and atomic % as shown in the inset table Fig 6(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 1 The DSSC utilized JDND2 as a photo-sensitizer (20 mg) yielded values of JSC, VOC, FF andhin the order of 2.2 mA cm 2,

805 mV, 60.4%, and 1.1%, respectively In general, photonic absorption of concentrated material will dominate those of mate-rials with lower concentrations as it was shown in the UVevis optical absorption studies presented already inFig 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 5 (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.

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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

nano-particles JDND1 (10 mg) in DSSC yielded a value of 1.2 mA cm 2for

JSC, which is lower than those obtained for the other two DSSCs

with JDND2 and JDND3, meaning the relatively lower

concentra-tion of JDND in DSSCs has resulted in a low photo-absorpconcentra-tion

While the concentration of photo-sensitizer increased from

10 mg to 20 mg in the photo-anode, JSCincreased 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 character-istics 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 JSCvalue and thus can lead to a maximum possible photovoltaic perfor-mance As it can be seen, all three DSSCs yieded better VOCvalues (~805 mVe824 mV) with decent values of FF (60%e64%) Here, JSC

is considred the only factor which controlled the overall perfor-mance 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 har-vesting 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 perfor-mance As prepared pristine JDND reported in the present work accounts no modifications in the dye in terms of purification and

Fig 6 (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 TiO 2 , EIS studies performed on the DSSCs showing (b) Nyquist and (c) Bode phase characteristics.

Table 1

Photovoltaic parameters measured under AM1.5 illumination condition.

Photo-sensitizer J SC (mA/cm 2 ) V OC (mV) FF (%) h(%)

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doping Thus, the lower JSCvalues 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

concen-trations The charge transfer and recombination resistive

charac-teristics in the DSSCs can be realized from the Nyquist and Bode

phase plots shown inFig 6(b) and (c), respectively The size of the

semi-circles obtained from the three DSSCs shows that the

resis-tance 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 inFig 6(c) look similar in cases of DSSCs

uti-lizing JDND2 and JDND3 This is in good agreement with their

performance shown inFig 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

photo-sensitizer As the results show, the cobalt electrolyte can also yield

higher VOCbut lower JSCvalues than that of DSSCs using iodide as a hole transport material The DSSC with cobalt electrolyte yield values of JSC, VOC, FF andhin the order of 0.4 mA cm 2, 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 electro-lyte 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 photo-voltaic technology The JDND extracted from the rags of jackfruit waste shows decent JSCand higher VOCvalues 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 2 summarizes few important natural dye sources and their applica-tion in DSSCs with maximum reportedhvalues

Fig 7 (a) JeV characteristic of the DSSCs with cobalt electrolyte, EIS studies performed on the DSSCs show the (b) Nyquist and (c) Bode phase characteristics.

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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 ofhof 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 JSCand the overall

per-formance of the DSSC can be further improved if chemical puri

ﬁ-cation 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

per-formance 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

photo-sensitizer reported in this work, it is expected to be cost

effec-tive 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

ob-tained from the DSSCs utilized JDND as a photo-sensitizer such

as JSC, VOCand 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

4 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 photo-sensitizers 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 Ram-alingaswamy fellowship grant

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Table 2

Photovoltaic performance of well-known natural dyes reported.

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