Accepted Manuscript Stability and efficiency of dye-sensitized solar cells based on papaya-leaf dye Suyitno, Trisma Jaya Saputra, Agus Supriyanto, Zainal Arifin PII: DOI: Reference:

S1386-1425(15)00422-9 http://dx.doi.org/10.1016/j.saa.2015.03.107 SAA 13522

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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

4 September 2014 9 March 2015 27 March 2015

Please cite this article as: Suyitno, T.J. Saputra, A. Supriyanto, Z. Arifin, Stability and efficiency of dye-sensitized solar cells based on papaya-leaf dye, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.03.107

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Stability and efficiency of dye-sensitized solar cells based on papaya-leaf dye Suyitno1,a, Trisma Jaya Saputra1, 2, Agus Supriyanto3, Zainal Arifin1 1

Department of Mechanical Engineering, Sebelas Maret University 2 Department of Physics, Sebelas Maret University Jl. Ir. Sutami 36A Surakarta, Indonesia 3 Department of Mechanical Engineering, Tidar University Jl. S. Parman, 39 Potrobangsan, Magelang, Indonesia a [email protected], Phone: +62 8170621951

Abstract The present article reports on the enhancement of the performance and stability of natural dye-based dye-sensitized solar cells (DSSCs). Natural dyes extracted from papaya leaves (PL) were investigated as sensitizers in TiO2-based DSSCs and evaluated in comparison with N719 dye. The acidity of the papaya-leaf extract dyes was tuned by adding benzoic acid. The TiO2 film-coated fluorine-doped tin oxide glass substrates were prepared using the doctor-blade method, followed by sintering at 450°C. The counter electrode was coated by chemically deposited catalytic platinum. The working electrodes were immersed in N719 dye and papaya dye solutions with concentrations of 8 g/100 mL. The absorbance spectra of the dyes were obtained by ultra-violet–visible spectroscopy. The energy levels of the dyes were measured by the method of cyclic voltammetry. In addition, Fourier transform infrared spectroscopy was used to determine the characteristic functionalities of the dye molecules. The DSSC based on the N719 dye displayed a highest efficiency of 0.87% whereas those based on papaya-leaf dye achieved 0.28% at pH 3.5. The observed improved efficiency of the latter was attributed to the increased current density value. Furthermore, the DSSCs based on papaya-leaf dye with pH 3.5–4 exhibited better stability than those based on N719 dye. However, further studies are required to improve the current density and stability of natural dye-based DSSCs, including the investigation of alternative dye extraction routes, such as isolating the pure chlorophyll from papaya leaves and stabilizing it. Keywords: Solar light energy conversion; Dye-sensitized solar cells; Papaya-leaf dye; Efficiency;

Stability. 1. Introduction Because of their simplicity and sufficiently high efficiency, dye-sensitized solar cells (DSSCs) constitute promising devices for the conversion of light into electrical energy. For the sensitization of the semiconductor material, expensive ruthenium-based complex dyes, such as N719 and N3, are typically used. Owing to their abundant availability and easy extraction process, natural dyes containing leaf, fruit, and flower extracts have been actively studied and tested as low-cost and promising sensitizers for DSSCs. For this purpose, they must have the following required properties: a broad absorption response in the visible-light region [1], high content of the anthocyanin and chlorophyll groups [1], high chemical stability [2], high compatibility with both the solvent [2] and the semiconductor [3, 4], and a short-chain molecular configuration [3, 5]. Various natural dyes have been studied and developed for DSSCs, typically resulting in efficiencies of less than 1%. Ipomoea-leaf extract-based DSSCs have been measured to have an efficiency of 0.318% [3]. The efficiency of DSSCs based on pomegranate leaves, red Sicilian orange, purple eggplant, K. japonica, and R. chinensis extracts was 0.597% [1], 0.66% [5], 0.48% [5], 0.22% [4], and 0.29% [4], respectively. The differences in the energy conversion efficiencies of natural dye-based DSSCs have been widely discussed in terms of differences in their light absorbance, tested by ultra-violet–visible (UV–Vis) spectrophotometry. Nevertheless, the light absorbance alone does not provide an adequate explanation for the voltage and current density variations displayed by 1

DSSCs and further factors, such as the binding energy, anchorage, and energy level between the dye and the TiO2 electrode [3, 6], must be taken into account. However, the quantification of the binding energy or anchorage between natural dyes and TiO2 surfaces is not a simple issue since natural dyes usually consist of many complex groups. In addition to their efficiency, the stability of DSSCs is also a key consideration. The short-circuit current density (Jsc) of anthocyanin dye-based DSSCs dropped from the original 0.91 mA/cm2 to 0.73 mA/cm2 and to 0.45 mA/cm2 after being subjected to irradiation for 30 and 120 min, respectively [3]. In contrast, orange juice and eggplant acidic extract dye-based DSSCs remained stable under irradiation with AM 1.5 for 3 and 6 h, respectively [5]. To overcome the problem of the instability of natural dye-based DSSCs, various techniques have been examined, for example, the addition of sugar [4]. Besides being more stable, anthocyanin dye-based DSSCs with added sugar displayed an additional slight increase of efficiency. Another method proposed the addition of HCl into the anthocyanin dye to adjust the pH to approximately 1, because the formation of the flavylium ion form is favorable at low pH [2]. Unfortunately, unlike benzoic acid (C6H5COOH), HCl contains no carboxylic functional groups to act as anchorage between the dyes and the TiO2 surfaces. Therefore, the stability and energy conversion efficiency are two important concerns for utilizing natural dyes as photosensitizers for DSSCs. In this work, the performance and stability of chlorophyll-based natural dyes in TiO2-based DSSCs was studied. The dyes were extracted from papaya leaves and the dye acidity was controlled by adding benzoic acid. The performance and stability of the natural dye-based DSSCs were compared with those of N719-based DSSCs. 2. Materials and Methods 2.1. Preparation and testing of dyes The dye extraction from papaya leaves (PL) was carried out as follows: the raw material (~35 g) was first added to ethyl alcohol (350 mL, 96%, Merck, Germany) and heated at 70°C for 3 h. The extracted dyes were then isolated from the ethanolic solution by rotary evaporation. Afterwards, the PL extracts were mixed with ethyl alcohol (96%, Merck, Germany) until the required concentration of 8 g/100 mL [7] was obtained. The acidification of the dyes was performed by adding benzoic acid to obtain the required pH; namely, 5.5, 5.0, 4.5, 4.0, 3.5, and 3.0. The synthetic dye used in the tests was N719 (Dyesol). A UV-Vis spectroscopy system (Lambda 25, Perkin Elmer) was used to test the light absorbance properties of the dyes. Fourier transform infrared spectroscopy (FTIR, Shimadzu) was implemented to confirm the presence of the functional groups in the dyes. Cyclic voltammetry (CV, Metrohm AG) was used to determine the reduction and oxidation potentials (Ered, Eox) and the peak cathodic and anodic currents (Ipc, Ipa) of the dyes, while a pH meter (AD-110 Adwa) was utilized for the measurement of their pH.

2.2. DSSC fabrication and testing The DSSCs consisted of a conducting glass, the TiO2 dye-absorbing electrode, the electrolyte, and a counter-electrode layer. The fluorine-doped tin oxide (FTO), used as the conducting glass substrate, was prepared using spray pyrolysis [8, 9]. A solution of tin (II) chloride dihydrate (16.116 g, Cl2Sn·2H2O, Merck), ammonium fluoride (0.265 g, NH4F, Merck), and ethyl alcohol (100 mL, 96%, Merck) of 100 mL was mixed and sprayed on the glass surface, followed by heating at 450°C. To prepare the catalytic platinum counter electrode, the FTO glass was first heated at 200°C. Platinum was then chemically deposited from a 5 mM H2PtCl6 solution (Merck) onto the FTO glass, followed by heating at 300°C and subsequent cooling [10]. For the fabrication of the TiO2 working electrode, a homogenous paste containing TiO2 semiconductor (0.5 g) and ethyl alcohol (0.4 mL, 96%, Merck) was prepared. The diameter of the used TiO2 nano powder (Sigma-Aldrich) was 21 nm. The paste was then cast onto the FTO glass (1 cm × 3 cm) using the doctor-blade method with the thickness of the TiO2 film maintained at 20 µm. For a strong bonding between the TiO2 film particles and the FTO glass [1, 3], the TiO2 paste-coated 2

FTO glass was sintered at 450°C for 2 h [2, 3] and subsequently cooled. Afterwards, the TiO2 working electrodes were immersed in the respective dye solutions for 24 h at room temperature, prior to the DSSC assembly. The electrolyte solutions for the DSSCs were prepared as follows: sodium iodide (3.30 g, 99.95%, Merck) and acetonitrile (30 mL) were dissolved by stirring for 15 min, prior to adding iodine (523.88 g, 99.95%, Merck) and tungstophosphoric acid hydrate (5.48 mg, H3O40PW12·xH2O, Merck). The stirring was continued for 24 h to achieve a homogeneous solution. The electrolyte solution was injected into the assembled DSSC at 50-µm spaced intervals and then sealed. The voltage and current of the DSSCs were recorded with a Keithley 2602A meter (USA) under illumination by a lamp of 1000 W/m2. The efficiency of the DSSCs was determined from the open-circuit voltage (Voc) and Jsc measurements and the calculated fill factor (FF) values. For the stability tests, the DSSCs were subjected to illumination for 100 h using lamps of 1000 W/m2 at a temperature of 50°C. 3. Results and Discussion 3.1. UV-Vis Spectra of Dyes PL dyes have an intense absorption maximum at approximately 464 nm as shown in Fig. 1, known as Soret band. The second spectra peak of the PL dyes found at wavelengths 660 nm and similar to the Q bands of Chlorophyllins [4]. The addition of benzoic acid to the PL dyes has minor effect to the absorption spectra of the PL dyes revealing that the optical properties of PL dyes are almost the same. In addition, the absorption spectra peak of N719 dye is at a wavelength of 518 nm. Meanwhile, Fig. 2 shows that there are differences in the ability of the dye to adsorb onto the TiO₂ semiconducting layer for 24 hours resulting in a change in the intensity of the absorption spectra. The Soret and Q bands are not seen in the spectra of the dyes on TiO₂ showing that the dyes have formed good bonding with TiO₂ surfaces.

Fig. 1. Absorption spectra of N719 and PL dyes.

Fig. 2. Absorption spectra of dyes on TiO₂ semiconductor and TiO₂ semiconductor on fluorine doped tin oxide (FTO).

3.2. Performance of DSSCs The performance parameters of the DSSCs are shown in Table 1 and Fig. 1. The average voltage produced from the N719 dye-based DSSC was higher than those from the PL dye-based DSSCs. Increasing the acidity of the natural dyes produced a higher voltage, achieving the highest value of 490 mV for the pH 5.0 natural dye-based DSSC. The value of Voc depends on the energy levels of the highest occupied molecular orbital (EHOMO) and lowest unoccupied molecular orbital (ELUMO); these were tested using CV and the results are shown in Table 2. The HOMO acting as the ground state is the highest energy molecular orbital (MO) containing at least one electron. Correspondingly, the LUMO is the lowest energy orbital where electrons excite. Table 1 Performance parameters of PL extract and N719 dye-based DSSCs. Dyes Voc (mV) Jsc (mA/cm2) FF η (%) N719 475 3.40 0.54 0.87 PL dye (as extracted) 325 0.36 0.56 0.07 PL dye with pH 5.5 400 0.51 0.52 0.11 PL dye with pH 5.0 490 0.66 0.51 0.17 PL dye with pH 4.5 415 0.90 0.56 0.21 PL dye with pH 4.0 415 0.98 0.54 0.22 PL dye with pH 3.5 460 1.19 0.52 0.28 PL dye with pH 3.0 430 1.10 0.55 0.26

Fig. 3. Current-voltage curves of the examined DSSCs. Table 2 HOMO, LUMO, Ipc, and Ipa measured by CV. Eox EHOMOa Ered ELUMOb EBand Gap Dyes (V) (eV) (V) (eV) (eV) N719 0.78 -5.18 -1.33 -3.07 2.10 PL dye (as extracted) 0.68 -5.08 -1.63 -2.77 2.30 PL dye with pH 5.5 0.50 -4.90 -1.70 -2.70 2.20 PL dye with pH 5.0 0.53 -4.93 -1.78 -2.62 2.31 PL dye with pH 4.5 0.46 -4.86 -1.80 -2.60 2.26 PL dye with pH 4.0 0.49 -4.89 -1.70 -2.70 2.19 PL dye with pH 3.5 0.46 -4.86 -1.70 -2.70 2.16 PL dye with pH 3.0 0.52 -4.92 -1.58 -2.82 2.10 a    4.4 b    4.4

Ipc (A) 1.89 × 10-4 1.80 × 10-3 4.44 × 10-3 4.38 × 10-3 4.65 × 10-3 4.67 × 10-3 4.41 × 10-3 4.16 × 10-3

Ipa n= (A) |Ipc/Ipa| -3.03 × 10 -4 0.62 -2.76 × 10 -3 0.65 -1.87 × 10 -3 2.37 -1.80 × 10 -3 2.44 -1.86 × 10 -3 2.51 -1.86 × 10 -3 2.52 -1.78 × 10 -3 2.48 -1.70 × 10 -3 2.44

It is well known that the Voc of solar cell devices is directly proportional to the energy gap between the HOMO and the LUMO [11]. The electrochemical oxidation and reduction onset potentials (Eox and Ered) determined from CV results are used to calculate HOMO and LUMO levels. The onset potentials are determined from the intersection of tangents between rising current and baseline charging current of the CV curves. As shown in Table 2, the ELUMO level of the N719 dye was lower than that of the PL dye, which should cause a lower Voc for the N719 dye-based DSSCs. However, Fig. 4 indicates that the higher EHOMO level of the PL dyes might inhibit the charge carrier regeneration and transfer from the electrolyte into the dyes. Consequently, the voltage produced by the N719 dye-based solar cells was greater than that of the PL dye-based ones. The addition of benzoic acid to increase the acidity of the PL dyes significantly changed the position of the EHOMO and ELUMO levels of the dyes. The energy gap between the HOMO-LUMO levels of the dyes and the electrolytes was the main cause of the high Voc generated from the solar cells with PL dye and pH 5. Therefore, the EHOMO and ELUMO levels of the dyes, the TiO2 semiconductors, and the electrolytes should be tuned carefully to minimize the energy loss and to produce high Voc [11].

Fig. 4. Electron transfer scheme of the examined DSSCs. Regarding the magnitude of Jsc, the N719 dye solar cells had the highest Jsc value, while the increase of the acidity of the PL dyes by adding benzoic acid also significantly increased the Jsc. Many previous studies observed that the Jsc has a significant influence on the absorption capability of the dyes [1-4, 9]. However, Fig. 5 (a) shows that the light harvesting efficiency (LHE = 1-10-A, where A is the light absorbance for each dye) of the examined dyes had a minor effect on the Jsc. Furthermore, the ability to absorb light was higher for the PL dyes and was not significantly affected by the addition of benzoic acid. In contrast, the acidity has a significant effect on the HOMO and LUMO energy levels of the dyes, as shown in Table 2. Particularly, the LUMO energy level can influence the injection of electrons into the conduction band (CB) of TiO2 [6]. Greater LUMO energy levels of the dye might increase the voltage difference between the dye and the electrolyte, facilitating the electron transfer between the dye and the TiO2. Nevertheless, the Jsc value of the N719 dye-based DSSC was three times higher than that of the PL dye-based DSSCs.

Fig. 5. Light harvesting efficiency of the dyes after illumination for (a) 0 h and (b) 100 h. Besides the effect on the HOMO and LUMO energy levels, the acidity affects the Ipc and Ipa of the dyes. As can be seen in Table 2, the ratio n of the cathodic to the anodic peak currents of the N719 and the as-extracted PL dye had almost matching values of 0.62 and 0.65, respectively. This indicates that the redox reaction in both dyes was irreversible. As expected, the PL dyes with high acidity exhibited significantly increased Ipc and therefore PL dyes with low pH (up to pH 4) had a high ratio n, which decreased for stronger acidity. Consequently, up to pH 4, the effect of acidity on the dye was to improve Ered and enhance its reversibility. Ipc/Ipa > 2 also shows that the electrons in the dye (EHOMO) were more easily regenerated by the electrolytes. Good contact (anchor) between the dye and the semiconductor in DSSCs is necessary to provide fast and efficient injection of electrons. Solar cell dyes must contain at least one functional group (e.g., –COOH, –SO3H, –PO3H2, or –Si(OEt)3) to ensure good absorption of the dye on the semiconductor surface and produce good electron communication [6]. The FTIR measurements of Fig. 6 show that all dyes display sharp peaks in both the 2500–3000 cm-1 and 1600–1750 cm-1 regions, which correspond to the presence of the –OH and C=O groups, respectively. However, the

amount of C=O stretching and –OH groups found in the PL dyes without benzoic acid were lower than those in the N719 dye. In the latter, the -COOH groups had the hydroxyl anchor on the TiO2, producing the ester and increasing the effect of the electron clutching on the CB of TiO2, thus enabling a fast and efficient electron transfer [3]. The striking difference between the N719 dye and the PL (as extracted) dye was the presence of substantial C-N stretching found in chlorophyll. As a result, the Jsc from the PL dye-based DSSC was lower than that from the N719 dye-based DSSC.

Fig. 6. FTIR spectra of N719 and PL dyes at 0 h. Fig. 6 also indicates that the addition of benzoic acid to the PL dyes increased the amount of –OH groups and C=O stretching and reduced the amount of C-N stretching. Consequently, the Jsc of the DSSCs with a small pH (more acid) increased sharply. In contrast, the amount of –OH groups and C=O stretching in the dye with pH 3.0 again decreased, which might be due to the destruction of the groups because of the high acidity conditions. The smaller amounts of –OH groups and C=O stretching found in the dyes, the lower Jsc was generated from the DSSCs. As observed in Table 1, the N719 dye-based DSSC displayed superior efficiency (~12 times higher) than the PL dye-based DSSCs; it also displayed the highest current and voltage. Regardless, the measured efficiency of the N719 dye-based DSSC (0.87%) remains lower than those achieved by other synthetic-dye TiO2-based DSSCs (up to 12%) [12]. The size and shape of the semiconductor electrode, thickness of the semiconductor layer, and immersion times in the dye solutions are known to influence the performance of the device. Regarding the efficiency of the examined natural dye-based DSSCs, the present comparison study determined that the PL-based dye with pH 3.5 produced the most efficient solar cells (0.28%). The measured efficiencies (0.07–0.28%) are lower than several values reported in the literature: 0.09–1.47% with 20 natural dyes [13], 0.03–1.17% with Pomegranate leaves and Mulberry fruit dyes [1], 0.81% with zinc chlorophyll dyes [14], 0.88% with chlorophyllins dyes [15], 0.54–0.97% with Kerria japonica and Rosa chinensis flower dyes [4], and 1.47% with Lawsonia inermis seed dyes [16]. These differences could be influenced by factors like the type and shape of semiconductor, the electrical resistance property of the solar cells, and the molecular structure of the dyes. In contrast, the present results are higher or comparable to those reported in other studies: 0.043% with Tamarillo extract dyes [17], 0.034–0.054% with anthocyanin dyes [18], and 0.16% with Raspberry fruit and Rosella flower dyes [19]. This improved efficiency is believed to be due to the higher generated Jsc [20] and significantly affected by the HOMO-LUMO energy levels of the dyes, the energy levels of the semiconductors and the electrolytes, and the anchorage between semiconductors and dyes. 3.3. Stability of DSSCs

The stability test was conducted by placing the DSSCs in a luminous room under irradiation with 1000 W/m2 for 100 h at a temperature of 50°C. Afterwards, the performance of the DSSCs was measured (Table 3). The results of Table 3 indicate that the efficiency of the PL dye-based DSSCs decreased more than 71% owing to a decrease in the voltage and current. Meanwhile, the efficiency of the N719 dye-based DSSC decreased more than 35% mainly because of a decrease in the current. Interestingly, the PL dye-based DSSCs with pH 3.5 featured the lowest performance degradation. Table 3 Performance of DSSCs after treatment for 100 h. Voc Jsc Dyes (mV) Degradation (mA/cm2) Degradation N719 470 1.1% 1.58 53.5% PL dye (as extracted) 132 59.4% 0.14 61.1% PL dye with pH 5.5 304 24.0% 0.24 52.9% PL dye with pH 5.0 380 22.4% 0.36 45.5% PL dye with pH 4.5 380 8.4% 0.45 50.0% PL dye with pH 4.0 399 3.9% 0.47 52.0% PL dye with pH 3.5 440 4.3% 0.55 53.8% PL dye with pH 3.0 400 7.0% 0.43 60.9%

(%) 0.56 0.02 0.07 0.11 0.14 0.16 0.23 0.14

η Degradation 35.6% 71.4% 36.4% 35.3% 33.3% 27.3% 17.9% 46.2%

Fig. 5 (b) shows that the treatment affected the light harvesting efficiency of the PL dyes only, which increased due to the shifting of the initially green color to a darker green. No significant change was observed in the LHE of the N719 dye. However, the FTIR spectra of the treated dyes revealed that C-H, C-O, and C-C stretching were drastically degraded, as can be seen in Fig. 7. The PL dye-based DSSCs with pH 3.5 and 4 achieved good stability, while for pH 3 the stability was poor; this might be due to the degradation of C-H and C-O stretching, which weakened the anchor and inhibited the electron transfer between the dye and the semiconductor.

Fig. 7. FTIR spectra of the dyes after the stability test (illumination for 100 h). The stability test resulted in changes of the LUMO and HOMO energy levels of all dyes, as can be seen in Table 4. The low energy levels of LUMO and HOMO caused the voltage between the electrolyte and the dye to diminish. Moreover, while the value of n for the N719 dye did not change after the stability test and remained within the range from 0.62 to 0.65, for the PL dyes it drastically decreased, ranging from 0.39 to 0.55. After the treatment, the Ipc from the PL dyes sharply decreased,

leading to a reduced number of electrons being transferred, i.e., a reduced current. Since hardly any electrons were generated in the dye (EHOMO), the performance of the DSSCs decreased. Table 4 HOMO, LUMO, Ipc, and Ipa of the dyes after treatment for 100 h, measured by CV. Eox EHOMO Ered ELUMO EBand Gap Ipc Ipa n= Dyes (V) (eV) (V) (eV) (eV) (A) (A) |Ipc/Ipa| N719 0.91 -5.31 -1.12 -3.28 -2.03 2.17 × 10-4 -3.50 × 10-4 0.62 PL dye (as extracted) 1.04 -5.44 -1.58 -2.82 -2.62 2.62 × 10-3 -4.80 × 10-3 0.55 PL dye with pH 5.5 0.94 -5.34 -1.23 -3.17 -2.17 2.04 × 10-3 -5.04 × 10-3 0.41 PL dye with pH 5.0 0.95 -5.35 -1.13 -3.27 -2.08 1.93 × 10-3 -4.80 × 10-3 0.40 PL dye with pH 4.5 0.98 -5.38 -1.11 -3.29 -2.09 1.92 × 10-3 -4.80 × 10-3 0.40 PL dye with pH 4.0 1.02 -5.42 -1.18 -3.22 -2.2 1.92 × 10-3 -4.80 × 10-3 0.40 PL dye with pH 3.5 1.02 -5.42 -1.14 -3.26 -2.16 1.83 × 10-3 -4.51 × 10-3 0.41 PL dye with pH 3.0 0.96 -5.36 -1.19 -3.21 -2.15 1.79 × 10-3 -4.40 × 10-3 0.41 4. Conclusions The performance and the stability of PL dye-based DSSCs was investigated and compared with N719 dye-based DSSCs. The performance of the synthetic N719 dye-based DSSC achieved an efficiency of 0.87%, whereas the highest efficiency recorded amongst the PL dye-based DSSCs was 0.28% at pH 3.5. The main variable contributing to this large difference in the measured efficiencies was the current density, which was determined not only by the LHE properties of the dyes but also by their –COOH functionalities and their HOMO-LUMO energy levels. Furthermore, the addition of benzoic acid increased the acidity of the PL dyes up to pH 3.5, improving the performance of the DSSCs up to four times. The PL dye-based DSSCs with pH 3.5–4 displayed better stability than the N719 dye-based ones. Further studies to improve the efficiency and stability of natural dye-based DSSCs could include the investigation of alternative dye extraction routes, such as isolating the pure chlorophyll from papaya leaves and stabilizing the pure chlorophyll. Acknowledgement The authors thank the Rector of Sebelas Maret University and LPDP (Indonesia Endowment Fund for Education) No. PRJ-755/LPDP/2014 for supporting the funding for doing the research. References [1] H. Chang, Y.J. Lo, Pomegranate leaves and mulberry fruit as natural sensitizers for dye-sensitized solar cells, Sol. Energy, 84 (2010) 1833–1837. [2] K. Wongcharee, V. Meeyoo, S. Chavadej, Dye-sensitized solar cell using natural dyes extracted from rosella and blue pea flowers, Sol. Energy Mater. Sol. Cells, 91 (2007) 566-571. [3] H. Chang, H.M. Wu, T.L. Chen, K.D. Huang, C.S. Jwo, Y.J. Lo, Dye-sensitized solar cell using natural dyes extracted from spinach and ipomoea, J. Alloys Compd., 495 (2010) 606–610. [4] K.V. Hemalatha, S.N. Karthick, C.J. Raj, N.Y. Hong, S.K. Kim, H.J. Kim, Performance of Kerria japonica and Rosa chinensis flower dyes as sensitizers for dye-sensitized solar cells, Spectrochim. Acta A, 96 (2012) 305–309. [5] G. Calogero, G.D. Marco, Red Sicilian orange and purple eggplant fruits as natural sensitizers for dye-sensitized solar cells, Sol. Energy Mater. Sol. Cells, 92 (2008) 1341– 1346. [6] Y. Ooyama, Y. Harima, Photophysical and Electrochemical Properties, and Molecular Structures of Organic Dyes for Dye-Sensitized Solar Cells, ChemPhysChem, 13 (2012) 4032 – 4080. [7] K.E. Jasim, S. Al-Dallal, A.M. Hasan, Henna (Lawsonia inermis L.) Dye-Sensitized Nanocrystalline Titania Solar Cell, J. Nanotechnology, 2012 (2012). 9

[8] A.V. Moholkar, S.M. Pawar, K.Y. Rajpure, C.H. Bhosale, J.H. Kim, Effect of fluorine doping on highly transparent conductive spray deposited nanocrystalline tin oxide thin films, Appl. Surf. Sci., 255 (2009) 9358–9364. [9] Suyitno, Z. Arifin, A.A. Santoso, A.T. Setyaji, Ubaidillah, Optimization Parameters and Synthesis of Fluorine Doped Tin Oxide for Dye-Sensitized Solar Cells, Applied Mechanics and Materials, 575 (2014) 689-695. [10] P. Calandra, G. Calogero, A. Sinopoli, P.G. Gucciardi, Metal nanoparticles and carbon-based nanostructures as advanced materials for cathode application in dye-sensitized solar cells, Int. J. Photoenergy, 2010 (2010) 1-15. [11] W.C.H. Choy, Organic Solar Cells: Materials and Device Physics, in, Springer, London, 2013. [12] M. Gratzel, Photovoltaic performance and long term stability of dye-sensitized mesoscopic solar cells, C. R. Chimie, 9 (2006) 578–583. [13] H. Zhou, L. Wu, Y. Gao, Dye-Sensitized Solar Cell Using 20 Natural Dyes as Sensitizer, J. Photochem. Photobiol., A, 219 (2011) 188–194. [14] S. Erten-Ela, O. Vakuliuk, A. Tarnowska, K. Ocakoglu, D.T. Gryko, Synthesis of zinc chlorophyll materials for dye-sensitized solar cell applications, Spectrochim. Acta A, 135 (2015) 676–682. [15] G. Calogero, I. Citro, C. Crupi, G.D. Marco, Absorption spectra and photovoltaic characterization of chlorophyllins as sensitizers for dye-sensitized solar cells, Spectrochim. Acta A, 132 (2014) 477–484. [16] S. Ananth, P. Vivek, T. Arumanayagam, P. Murugakoothan, Natural dye extract of lawsonia inermis seed as photo sensitizer for titanium dioxide based dye sensitized solar cells, Spectrochim. Acta A, 128 (2014) 420–426. [17] D. Susanti, M. Nafi’, H. Purwaningsih, R. Fajarin, G.E. Kusuma, The Preparation of Dye Sensitized Solar Cell (DSSC) from TiO2 and Tamarillo Extract, Procedia Chemistry, 9 (2014) 3–10. [18] R. Ahmadian, Estimating the impact of dye concentration on the photoelectrochemical performance of anthocyanin-sensitized solar cells: a power law model, J. Photonics Energ., 1 (2011) 1-11. [19] S. Tekerek, A. Kudret, Ü. Alver, Dye-sensitized solar cells fabricated with black raspberry, black carrot and rosella juice, Indian J. Phys, 85 (2011) 1469-1476. [20] M.R. Narayan, Review: Dye Sensitized solar cells based on natural photosensitizer, Renew. Sust. Energy Rev., 16 (2012) 208–215.

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Stability and efficiency of dye-sensitized solar cells based on papaya-leaf dye Suyitno1,a, Trisma Jaya Saputra1, 2, Agus Supriyanto3, Zainal Arifin1 1

Department of Mechanical Engineering, Sebelas Maret University 2 Department of Physics, Sebelas Maret University Jl. Ir. Sutami 36A Surakarta, Indonesia 3 Department of Mechanical Engineering, Tidar University Jl. S. Parman, 39 Potrobangsan, Magelang, Indonesia a [email protected], Phone: +62 8170621951

Highlights: • • • • •

Dye-sensitized solar cells based on papaya-leaf and synthetic dyes were prepared. Papaya-leaf dyes of different acidities and N719 synthetic dye were used. Performance and efficiency measurements of these cells were performed. Highest efficiencies were 0.87% for N719 and 0.28% for papaya-leaf dye with pH 3.5. Excellent stability was obtained in the case of papaya-leaf dyes with pH 3.5–4.

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Stability and efficiency of dye-sensitized solar cells based on papaya-leaf dye.

The present article reports on the enhancement of the performance and stability of natural dye-based dye-sensitized solar cells (DSSCs). Natural dyes ...
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