Letter Cite This: ACS Appl. Energy Mater. 2019, 2, 3986−3990
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Enhancement of Photocurrent by Integration of an Artificial LightHarvesting Antenna with a Photosystem I Photovoltaic Device Yuya Takekuma,†,‡ Haruki Nagakawa,†,‡ Tomoyasu Noji,§,⊥ Keisuke Kawakami,§,# Rei Furukawa,∥ Mamoru Nango,§ Nobuo Kamiya,§ and Morio Nagata*,†
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†
Department of Industrial Chemistry, Graduate School of Engineering, Tokyo University of Science, 12-1 Ichigaya-funagawara, Shinjuku-ku, Tokyo 162-0826, Japan ‡ Photocatalyst Group, Local Independent Administrative Agency, Kanagawa Institute of Industrial Science and Technology (KISTEC), 407 East Wing, Innovation Center Building, KSP, 3-2-1 Sakado, Takatsu-ku, Kawasaki, Kanagawa 213-0012, Japan § The OCU Advanced Research Institute for Natural Science & Technology (OCARINA), Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan ∥ The University of Electro-Communications, Chofugaoka 1-5-1, Chofu, Tokyo 182-8585, Japan S Supporting Information *
ABSTRACT: Photosynthetic pigment−protein-based biophotovoltaic devices are attracting interest as environmentally friendly energy sources. Photosystem I (PSI), a photosynthetic pigment−protein, is a proven biophotovoltaic material because of its abundance and high charge separation quantum efficiency. However, the photocurrent of these biophotovoltaic devices is not high because of their low spectral response. We have integrated an artificial lightharvesting antenna into a PSI-based biophotovoltaic device to expand the spectral response. To fabricate the device, a perylene di-imide derivative (PTCDI) was introduced onto a TiO2 surface as an artificial antenna. In the photovoltaic cells formed by the PTCDI/PSI-assembled TiO2 electrode, the magnitude of the incident photon-to-current conversion efficiency spectrum was significantly enhanced in the range 450−750 nm, and the photocurrent increased to 0.47 mA/cm2. The result indicates that the photons absorbed by PTCDI transfer to PSI via Förster resonance energy transfer. KEYWORDS: photosystem I, biophotovoltaics, dye-sensitized solar cells, artificial antenna, FRET
B
The efficient unidirectional electron transfer of PSI is implemented in biophotovoltaic cells by the deposition of PSI onto the electrodes.8−12 These devices have been fabricated in the same way as dye-sensitized solar cells (DSSCs), which consist of a TiO2 semiconductor electrode, counter electrode, and redox mediator.13 For example, Mershin et al. reported PSI biophotovoltaics on nanostructured TiO2 and ZnO electrodes using a Co(II/III) redox mediator.8 The devices exhibited a short-circuit photocurrent density (JSC) of 0.362 mA/cm2. Furthermore, Yu et al. achieved the best JSC of 1.31 mA/cm2 by screen printing TiO2 onto a PSI-sensitized solar cell.9 In addition, Gizzie et al. reported a solid-state solar cell using polyaniline/TiO2.10 In addition to TiO2 electrodes, hematite semiconductor electrodes have also been investigated, and the resulting solar cell possesses a JSC of 0.0596 mA/cm2 with a 590 nm long-pass filter.11 However, the photocurrents
iophotovoltaic devices are powered by protein−pigment complexes such as reaction centers along with the surrounding antenna complexes (RC-LHI), photosystem I (PSI), and photosystem II (PSII) or by light-harvesting (LH) pigment−protein complexes such as LHCII and phycocyanin (PC).1−3 These natural materials are plentiful and pose no threat to the environment. Thus, biophotovoltaics have been gaining considerable research attention, and various types of biophotovoltaics have been investigated.4,5 One biophotovoltaic material, PSI, has attracted attention because of its abundance and high charge separation quantum efficiency. PSI, which is derived from cyanobacteria, has 96 chlorophyll (Chl) molecules in each monomeric subunit.6 Six of these molecules act as an electron transfer pathway, while the others play the role of an LH antenna. Photoenergy absorbed at the LH antenna is concentrated in a Chl dimer, known as the “special pair” (P700) via excitation energy transfer. The excited electron at P700 is transferred to the primary electron acceptor Chl-a (A0), the secondary acceptor phylloquinone (A1), and finally the acceptor [4Fe-4S] iron−sulfur clusters (FX, FA, and FB) with near unity quantum efficiency.7 © 2019 American Chemical Society
Received: February 20, 2019 Accepted: April 29, 2019 Published: April 29, 2019 3986
DOI: 10.1021/acsaem.9b00349 ACS Appl. Energy Mater. 2019, 2, 3986−3990
Letter
ACS Applied Energy Materials
immersed in the PTCDI solution, and then in the PSI buffer solution. PSI core complexes were purified from Thermosynechococcus vulcanus (T. vulcanus) according to previous methods19−21 with slight modifications. (For details, see the Supporting Information (SI).) As a control electrode, the PTCDI-TiO2 electrode was fabricated by immersion in PTCDI solution and subsequently in buffer solution without PSI. The absorption spectra of the fabricated TiO2 photoanodes were measured by UV−vis techniques. The spectrum of the TiO2 photoanode immersed in both PTCDI and PSI solution shows two main peaks at 575 and 675 nm (Figure 2a, blue
of these biophotovoltaic devices were not high because of their low spectral response. To compensate for the low spectral response of the reaction centers, the utilization of Förster resonance energy transfer (FRET) by artificial LH antennas has been investigated in a manner similar to that of photosynthetic organisms.14−17 This approach includes physically attaching the artificial antenna dye14−16 or quantum dots17 to the protein, and the photochemical activity of the protein has improved under the visible light that can be absorbed via FRET. In our previous study, we developed another approach (compositing artificial LH antenna in the form of a fluorescent dye, perylene di-imide derivative (PTCDI) with PSI solution) and demonstrated photohydrogen evolution.18 In this study, we integrated an artificial LH antenna, PTCDI, into a PSI-based biophotovoltaic device, which is incorporated by the adsorption of the fluorescence dye onto mesoporous TiO2. We showed that the spectral response and photocurrent of the biophotovoltaic device increased, thereby demonstrating enhanced photovoltaic performance. The integration design of the TiO2 photoanode is shown schematically in Figure 1. Construction on the TiO2 electrode was carried out by simply immersing the substrate sequentially in PTCDI and PSI solutions. The TiO2 electrode was first
Figure 2. (a) Absorption spectra measured for TiO2 electrodes with adsorbed PTCDI, PSI, and PTCDI/PSI. (b) Fluorescence spectra measured for ZrO2 electrodes with adsorbed PTCDI, PSI, and PTCDI/PSI under excitation at 540 nm. The stained ZrO2 electrodes were excited with an incidence angle of 30°. To remove second order diffracted light from the excitation light, a 540 nm band-pass filter was used. Background corrections were performed by using a ZrO2 electrode as a blank.
line). These peaks match the absorption spectra of PTCDI and PSI in the solution, respectively (Figure S2). This result indicates that both PTCDI and PSI were assembled onto TiO2. In addition, the PTCDI/PSI and PTCDI TiO2 photoanodes both exhibit broadening of absorption spectra due to dye aggregation. The emission spectrum of the fabricated ZrO2 electrode, which has surface properties that are comparable to those of TiO2 and a conduction band approximately 1.3 eV higher than that of TiO2, was measured (Figure 2b). In addition, the absorption spectra of these electrodes were measured (Figure S3). In the fluorescence spectrum of the PTCDI ZrO2 electrode under excitation at 540 nm, the broad band at
Figure 1. Structure of PSI and PTCDI, and schematic illustration of fabrication of the electrode surface. The photoenergy is absorbed by PTCDI and transferred to PSI via Förster resonance energy transfer, following which the photons are converted to electrons by PSI. The structure of PSI was drawn with a PDB ID 1JB0 file.6 3987
DOI: 10.1021/acsaem.9b00349 ACS Appl. Energy Mater. 2019, 2, 3986−3990
Letter
ACS Applied Energy Materials
from the PTCDI/PSI-assembled TiO2 electrode, the magnitude of the IPCE spectrum is significantly enhanced in the range 450−750 nm (Figure 3, blue line). This range matches the absorption range of the PTCDI/PSI-assembled electrode; thus, the high-intensity part of the solar spectrum can be used to generate electric power. Consequently, the best short-circuit current density (JSC) of the PTCDI/PSI photovoltaic device reaches 0.47 mA/cm2, and the PCE improves to 0.13%. It is suggested that the observed decrease in VOC of the device based on the PTCDI/PSI photoanode may be due to the increase of charge recombination by PTCDI. In DSSCs, sensitizing dye orientation and aggregation affect the device performance, in terms of the electron injection efficiency and charge recombination between TiO2 and dyes.25,26 As a result, low VOC values were observed in the cells with the adsorbed PTCDI dyes. According to the IPCE spectrum, the PTCDI appears to minimally increase the power of the PTCDI/PSI solar cells. From the J−V data, low JSC and VOC are also observed under AM 1.5G. However, in the PTCDI/PSI integrated photovoltaic, enhancement of the performance was observed. The observations that the PTCDI did not increase the power of the solar cell while PTCDI/PSI integration did imply that energy transfer occurs as seen in previous studies on DSSCs that applied an artificial LH antenna;27−29 that is, the photons absorbed by PTCDI might transfer to PSI via FRET in the PTCDI absorption range. The following energy transfer scheme is proposed: the photons absorbed by PTCDI are first transferred to peripheral antenna Chls, followed by photon accumulation at the P700 special pair.30 Electrons excited by P700 appear to be transferred and injected into the conduction band of the TiO2 film. We calculated the amounts of adsorbed PSI onto TiO2. The amounts were determined by absorbance for the solution prepared by desorbing PSI from the stained TiO2 electrode by using the acetone solution. These amounts were calculated to be 1.2 ± 0.12 μg Chl cm−2 for the PTCDI/ PSI substrate, and 1.5 ± 0.07 μg Chl cm−2 for the PSI substrate; i.e., the loading of PSI on PTCDI/PSI electrodes was lower than that on PSI electrodes. This suggests that the light energy might be efficiently accumulated into PSI. On the other hand, the PSI electron injection scheme of biosolar cells is as follows: the electron excited at the P700 site transfers to A0, A1, and iron−sulfur clusters and is then injected into TiO2 (Figure S5).9 In summary, the fluorescent dye, PTCDI, was integrated into a PSI-biophotovoltaic device to improve the low spectral response. The integration extended the spectral response of the photovoltaic device, and the photocurrent increased to 0.47 mA/cm2. Furthermore, the power conversion efficiency reached 0.13%. In this study, we showed that the imitation of the lightharvesting process of photosynthesis is efficient for biophotovoltaic devices. We believe that the development of these optimally designed composite structures of LH antennas and
600−800 nm was observed. In addition, the red-shift compared with that measured in chloroform solution was also observed. As a result of the red-shift, the fluorescence spectrum of PTCDI largely overlaps with the PSI absorption spectrum. This is expected to increase the energy transfer efficiency. The broad and red-shifted fluorescence is typical of the observation of excimers formed by π−π stacking of perylene di-imido derivatives.22,23 This implies that the PTCDI, which adsorbed onto ZrO2 and TiO2 without an anchoring group, adsorbed parallel to the ZrO2 and TiO2 and formed π−π stacks. In the PTCDI/PSI assembly electrode, a decrease in PTCDI fluorescence intensity at around 670 nm was observed. According to the absorption spectra of the PTCDI/PSI and PSI ZrO2 films, as shown Figure S3, the amounts of PTCDI hardly changed with and without PSI. Thus, these results may be attributed to the quenching of the PTCDI excimer. Moreover, in methanol solution, PTCDI was previously reported to be quenched in proportion to the concentration of PSI, following the Stern−Volmer equation.18 These results can be interpreted as evidence that the photons absorbed at PTCDI were transferred to PSI via FRET. The photovoltaic devices were fabricated by assembling a PTCDI/PSI-TiO2 photoanode and Pt counter electrode with Surlyn film. The electrolyte solution was injected through a hole drilled into the counter electrode. The electrolyte was an iodide/tri-iodide redox-based ionic liquid, reported previously (see the SI).12,24 The incident photon-to-current conversion efficiency (IPCE) spectra were measured (Figure 3) to
Figure 3. Incident photon-to-current conversion efficiency spectra of the biophotovoltaic devices using photoanodes with PTCDI, PSI, and PTCDI/PSI adsorbed onto TiO2.
evaluate the photovoltaic performance under monochromatic light. Moreover, the photocurrent-density−voltage (J−V) curve and characteristics under AM 1.5 G (100 mW cm−2 reference solar irradiation) are summarized in Figure S4 and Table 1, respectively. Remarkably, in photovoltaic cells formed
Table 1. Average Photocurrent Density−Voltage Characteristics under AM 1.5 Irradiation (100 mW/cm2) of the Biophotovoltaic Devices and Their Respective Standard Deviations for Eight Devices
PTCDI/PSI PSI PTCDI
JSC/mA cm−2
VOC/V
FF
PCE/%
0.43 ± 0.034 0.19 ± 0.0061 0.26 ± 0.034
0.43 ± 0.0024 0.61 ± 0.0067 0.45 ± 0.0054
0.62 ± 0.017 0.60 ± 0.014 0.59 ± 0.033
0.12 ± 0.011 0.070 ± 0.0038 0.070 ± 0.011
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DOI: 10.1021/acsaem.9b00349 ACS Appl. Energy Mater. 2019, 2, 3986−3990
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ACS Applied Energy Materials
(5) Wenzel, T.; Härtter, D.; Bombelli, P.; Howe, C. J.; Steiner, U. Porous translucent electrodes enhance current generation from photosynthetic biofilms. Nat. Commun. 2018, 9, 1299. (6) Jordan, P.; Fromme, P.; Witt, H. T.; Klukas, O.; Saenger, W.; Krauß, N. Three-dimensional structure of cyanobacterial photosystem I at 2.5 Å resolution. Nature 2001, 411, 909. (7) Hogewoning, S. W.; Wientjes, E.; Douwstra, P.; Trouwborst, G.; van Ieperen, W.; Croce, R.; Harbinson, J. Photosynthetic Quantum Yield Dynamics: From Photosystems to Leaves. Plant Cell 2012, 24, 1921−1935. (8) Mershin, A.; Matsumoto, K.; Kaiser, L.; Yu, D.; Vaughn, M.; Nazeeruddin, M. K.; Bruce, B. D.; Graetzel, M.; Zhang, S. Selfassembled photosystem-I biophotovoltaics on nanostructured TiO2 and ZnO. Sci. Rep. 2012, 2, 234. (9) Yu, D.; Wang, M.; Zhu, G.; Ge, B.; Liu, S.; Huang, F. Enhanced photocurrent production by bio-dyes of photosynthetic macromolecules on designed TiO2 film. Sci. Rep. 2015, 5, 9375. (10) Gizzie, E. A.; Scott Niezgoda, J.; Robinson, M. T.; Harris, A. G.; Kane Jennings, G.; Rosenthal, S. J.; Cliffel, D. E. Photosystem Ipolyaniline/TiO2 solid-state solar cells: simple devices for biohybrid solar energy conversion. Energy Environ. Sci. 2015, 8, 3572−3576. (11) Ocakoglu, K.; Krupnik, T.; van den Bosch, B.; Harputlu, E.; Gullo, M. P.; Olmos, J. D. J.; Yildirimcan, S.; Gupta, R. K.; Yakuphanoglu, F.; Barbieri, A.; Reek, J. N. H.; Kargul, J. Photosystem I-based Biophotovoltaics on Nanostructured Hematite. Adv. Funct. Mater. 2014, 24, 7467−7477. (12) Kondo, M.; Amano, M.; Joke, T.; Ishigure, S.; Noji, T.; Dewa, T.; Amao, Y.; Nango, M. Immobilization of photosystem I or II complexes on electrodes for preparation of photoenergy-conversion devices. Res. Chem. Intermed. 2014, 40, 3287−3293. (13) O’Regan, B.; Gratzel, M. A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature 1991, 353, 737− 740. (14) Milano, F.; Tangorra, R. R.; Hassan Omar, O.; Ragni, R.; Operamolla, A.; Agostiano, A.; Farinola, G. M.; Trotta, M. Enhancing the Light Harvesting Capability of a Photosynthetic Reaction Center by a Tailored Molecular Fluorophore. Angew. Chem., Int. Ed. 2012, 51, 11019−11023. (15) Hassan Omar, O.; la Gatta, S.; Tangorra, R. R.; Milano, F.; Ragni, R.; Operamolla, A.; Argazzi, R.; Chiorboli, C.; Agostiano, A.; Trotta, M.; Farinola, G. M. Synthetic Antenna Functioning As Light Harvester in the Whole Visible Region for Enhanced Hybrid Photosynthetic Reaction Centers. Bioconjugate Chem. 2016, 27, 1614−1623. (16) Carey, A. M.; Zhang, H.; Liu, M.; Sharaf, D.; Akram, N.; Yan, H.; Lin, S.; Woodbury, N. W.; Seo, D. K. Enhancing Photocurrent Generation in Photosynthetic Reaction Center-Based Photoelectrochemical Cells with Biomimetic DNA Antenna. ChemSusChem 2017, 10, 4457−4460. (17) Nabiev, I.; Rakovich, A.; Sukhanova, A.; Lukashev, E.; Zagidullin, V.; Pachenko, V.; Rakovich, Y. P.; Donegan, J. F.; Rubin, A. B.; Govorov, A. O. Fluorescent Quantum Dots as Artificial Antennas for Enhanced Light Harvesting and Energy Transfer to Photosynthetic Reaction Centers. Angew. Chem., Int. Ed. 2010, 49, 7217−7221. (18) Nagakawa, H.; Takeuchi, A.; Takekuma, Y.; Noji, T.; Kawakami, K.; Kamiya, N.; Nango, M.; Furukawa, R.; Nagata, M. Efficient hydrogen production using photosystem I enhanced by artificial light harvesting dye. Photochemical & Photobiological Sciences 2019, 18, 309. (19) Shen, J.-R.; Kamiya, N. Crystallization and the Crystal Properties of the Oxygen-Evolving Photosystem II from Synechococcus vulcanus. Biochemistry 2000, 39, 14739−14744. (20) Kawakami, K.; Iwai, M.; Ikeuchi, M.; Kamiya, N.; Shen, J.-R. Location of PsbY in oxygen-evolving photosystem II revealed by mutagenesis and X-ray crystallography. FEBS Lett. 2007, 581, 4983− 4987. (21) Nagao, R.; Ishii, A.; Tada, O.; Suzuki, T.; Dohmae, N.; Okumura, A.; Iwai, M.; Takahashi, T.; Kashino, Y.; Enami, I. Isolation
energy-conversion reaction centers at the molecular levels can lead to more efficient photoenergy-conversion devices. Further investigation of the structures of PTCDI and PSI is needed for the development of photoenergy-conversion devices.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsaem.9b00349. PSI purification details, fabrication method of electrodes and biophotovoltaics, their corresponding photocurrent density−voltage curves, characterization details, and absorption spectra of dyes in solution and stained ZrO2 (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Haruki Nagakawa: 0000-0002-5845-8239 Tomoyasu Noji: 0000-0001-9468-2038 Nobuo Kamiya: 0000-0002-9056-7558 Morio Nagata: 0000-0001-6949-713X Present Addresses ⊥
T.J.: Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan. # K.K.: Research Center for Artificial Photosynthesis (ReCAP), Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan Author Contributions
Y. Takekuma, H. Nagakawa, and M. Nagata participated in the study design and conducted the experiments. Data were collected and analyzed by Y. Takekuma and M. Nagata. PSI of T. vulcanus was purified by T. Noji, K. Kawakami, M. Nango, and N. Kamiya. PTCDI was provided by R. Furukawa. All authors have given approval to the final version of the manuscript. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Y. Takekuma and M. Nagata would like to thank Mr. Ryo Koyama and Mr. Akira Matsuura (Department of Industrial Chemistry, Tokyo University of Science, Japan) for measuring the fluorescent quenching and device performance.
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REFERENCES
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