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Self-powered visual ultraviolet photodetector with Prussian blue electrochromic display† Lei Han, Lu Bai and Shaojun Dong*
Received 16th September 2013, Accepted 24th October 2013 DOI: 10.1039/c3cc47080f www.rsc.org/chemcomm
A novel self-powered ultraviolet (UV) photodetector was successfully constructed through combining Pt-modified TiO2 nanotubes and Prussian blue (PB)-modified ITO, in which the existence of UV could be judged easily by naked eye with the aid of PB for electrochromic display. More importantly, it could also self-recover without UV light illumination.
In the past decades, semiconductor-based photodetectors, one kind of optoelectronic device, have gained increasing attention owing to their potential applications in many aspects such as imaging techniques, chemical/biological sensing, optical communication and optoelectronic circuits.1–5 Generally there are two kinds of photodetector: photoconductor type and photodiode type.5–12 The former need to be driven by external power sources such as batteries and other energy storage/supply systems, which not only largely increase the system size but also greatly limit their mobility and independence for applications.13 In contrast, photodiode-type photodetectors such as p–n junctions and Schottky junctions can work without an external power supply, whereas their fabrication procedures require a fairly strict environment and sophisticated laboratory equipment with high operation costs.14,15 Thus it is still urgent to develop novel and simple routes to fabricate low-cost and high performance photodetectors. Photoelectrochemical cells (PECs) have been widely investigated as a new kind of green energy-conversion technology such as dye and quantum dot sensitized solar cells.16,17 Until recently, PECs have been proposed as a new type of self-powered photodetector due to their low-cost and simple manufacturing process.18,19 In these systems, F-doped tin oxide glass modified nanocrystalline TiO2 films were used as photoanodes. Upon light illumination with energy larger than the band gap, photogenerated electrons transfer from the valence band to the conduction band and then flow through an external circuit to the cathode. The photogenerated State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, University of the Chinese Academy of Sciences, Changchun 130022, Jilin, PR China. E-mail: [email protected] † Electronic supplementary information (ESI) available. See DOI: 10.1039/ c3cc47080f
802 | Chem. Commun., 2014, 50, 802--804
holes migrate to the electrode/electrolyte interface to oxidize electron donors in the electrolyte. It has been found that the performance of PEC-type self-powered photodetectors is much superior to that of photoconductivity-based photodetectors because their unique structure avoids the presence of a carrier depletion layer at the nanomaterial surface caused by surface trap states. In addition, Prussian blue (PB) is known to possess excellent electrochromic properties and a suitable redox reaction region, which make it a prominent candidate for electrochromic displays.20 Inspired by this, a novel self-powered and visual photodetector (SPVP) was successfully constructed by introducing PB into a PEC as one electrode and electrochromic display for the first time. Compared to previous PEC-type photodetectors, there are some advantages of our system. On the one hand, TiO2 nanotubes (TNTs) were chosen as the building blocks of the photodetector owing to their easy preparation and some distinct merits such as large surface-area and short electron diffusion length. On the other hand, whether UV exists or not could be observed directly by the color change of PB, where its original state is deep blue and the reduced state is transparent. The key to the successful operation of a SPVP is the rational selection of a semiconductor that can couple well with the electrochromic reaction. The principle of the selection is mainly based on the semiconductor band edge position versus the redox potential presented by the electrochromic reaction. Fig. 1 shows the general working principle of an SPVP based on a Pt-modified TiO2 nanotube photoanode (Pt/TNT) and a PB-modified ITO cathode (PB/ITO). Upon ultraviolet (UV) light illumination, a number of electron–hole pairs are generated (eqn (1)–(3)). Given that the TNTs possess suitable band structures,21 photogenerated holes could oxidize water to oxygen while photogenerated electrons flow through an external circuit to the cathode, where PB is reduced to Prussian white (PW) and the corresponding blue color becomes transparent. Thus we could judge the existence of UV through the color change of PB. It should be noted here that Pt/TNT could also be used as the cathode while PW reoxidizes in the dark. Among various noble metals, Pt possesses excellent electrocatalytic activity towards oxygen reduction, so we chose it to modify the TNT photoanode. When connected
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Fig. 1 General working principle of a self-powered, visual and selfrecovered photodetector.
with PW-modified ITO, the PW can be oxidized to PB whereas the electrons flow to the Pt/TNT cathode, which catalyzes oxygen reduction (eqn (4) and (5)). Based on the discussions above, a selfpowered, visual and self-recovered photodetector could be achieved. We first used an electrochemical anodic oxidation technique to prepare the TNT photoanode (Experimental section in ESI†).21 Then the Pt/TNT photoanode was synthesized by electrodepositing Pt nanoparticles (NPs) on the TNTs.22 As shown in Fig. S1A (ESI†), high density well-ordered and uniform nanotube structures could be observed. The diameter and wall thickness of these nanotubes were ca. 70 nm and 16 nm, respectively. Fig. S1B (ESI†) depicts an SEM image of the as-synthesized Pt/TNTs. It can be seen that Pt NPs of about 80 nm are randomly distributed on the surfaces of the TNTs. Fig. S2 (ESI†) reveals XRD patterns of the as-synthesized TNTs and Pt/TNT. For the TNTs, there are two diffraction peaks at about 2y = 25.41 and 48.11 corresponding to the (101) and (200) crystal faces of anatase TiO2 (JCPDS file: 89-4921), whereas the diffraction peaks at about 2y = 34.91 and 76.31 can be indexed to the crystal faces of rutile TiO2.21 In addition to these peaks, an additional two peaks at 46.41 and 67.81 were observed for Pt/TNT, which were ascribed to the (200) and (220) crystal faces of Pt (JCPDS file: 87-0646). These results demonstrated that Pt NPs were successfully deposited on the surfaces of the TNTs. Additionally, PB was electrodeposited on the ITO electrode as an electrochromic display layer. According to our previous reports,20 PB exhibits a broad absorption in the wavelength range of 500–800 nm. When applying a suitable negative bias, Fe(III) in PB was reduced to Fe(II) and the corresponding PB was converted to Prussian white (PW). Thus the absorbance decreased remarkably owing to the elimination of the intervalence charge transfer from Fe(III) to Fe(II). Meanwhile, the color changed from blue to transparent, indicating that PB could be used for electrochromic display. TiO2 + hn - e (TiO2) + h+(TiO2)
(1)
h+(TiO2) + 2H2O - O2 + 4H+
(2)
e (TiO2) + PB - PW
(3)
O2 + 4H+ + 4e - 2H2O
(4)
PW
e - PB
(5)
In order to validate the feasibility of the experiment design, we investigated the photoelectrochemical performance of Pt/TNT
This journal is © The Royal Society of Chemistry 2014
Fig. 2 (A) and (B) LSV collected from Pt-modified TiO2 nanotubes at a scan rate of 10 mV s 1 at applied potentials from 0.55 to 0.6 V vs. Ag/AgCl in 0.1 M PBS (pH = 6.0) containing 0.1 M KCl. (C) Cyclic voltammogram of PB/ITO in PBS at a scan rate of 10 mV s 1.
in a three-electrode cell with platinum foil as a counter electrode and Ag/AgCl (saturated KCl) as the reference electrode. Considering the stability of PB, we chose 0.1 M phosphate buffer solution (PBS) (pH = 6.0) containing 0.1 M KCl as the electrolyte throughout subsequent experiments. Fig. 2A shows the linear sweep voltammograms (LSV) recorded at the Pt/TNT electrode with and without UV light illumination from 0.55 V to 0.6 V at a scan rate of 10 mV s 1. There are two oxidation peaks between 0.55 V and 0.2 V, which were ascribed to hydrogen adsorption events at the Pt/TNT electrode, which further confirmed that Pt was successfully deposited on the surfaces of the TNTs. It can also be observed that there is an obviously enhanced oxidation photocurrent (0.4 mA cm 2) at 0 V vs. Ag/AgCl under UV light illumination compared to that in the dark, indicating a good photovoltaic performance. At the same time, we also investigated the Pt/TNT towards oxygen reduction through LSV. It can be seen from Fig. 2B that a large cathodic wave appears ( 0.09 mA cm 2) in air-saturated solution with the onset potential around 0.5 V vs. Ag/AgCl. As shown in Fig. 2C, the redox potential of PB lies around 0.21 V, which is just in the range from 0.1 V to 0.55 V. These results suggest that the as-prepared Pt/TNT electrode possesses good photoelectrocatalytic activity toward water oxidation at a low potential and electrocatalytic activity toward O2 reduction at a high potential. Therefore, it is reasonable to conclude that Pt/TNT could be used not only as a photoanode upon UV light illumination but also as a cathode in the dark to adjust the redox states of PB through electrons flowing from negative potential to a more positive potential (shown in Fig. 1). To demonstrate the self-powered and visual PEC-type photodetector concept, we combined PB/ITO with the dual functional Pt/TNT electrode to make a PEC. As shown in Fig. 3A, upon UV light illumination, decreased absorbance was observed because the reduction of Fe(III) in PB resulted in the elimination of the intervalence charge transfer from Fe(III) to Fe(II) causing its absorbance.20 In the dark, the absorbance returned to its
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Fig. 3 (A) Absorption response versus time during ten consecutive reproducible responses to ON–OFF light switch cycles with light intensity 10 mW cm 2. (B) The color change of the PB/ITO, (a): in the open circuit; (b): upon UV light illumination; (c): in the dark. Note: the absorbance of Prussian blue (PB) as baseline.
original state (Fig. 3A). In order to obtain clear information about the stability and responsiveness of the self-powered UV photodetector, ten consecutive reproducible responses to ON– OFF light switch cycles were performed. As shown in Fig. 3A, no obvious absorbance change was observed on periodically turning the UV light on and off with a power density of 10 mW cm 2 and the wavelength of 365 nm. What is more, the absorbance of PB decreased from 0 to 0.42 within 30 s and it could be recovered within 80 s. It can also be clearly seen that the color changed from blue to colorless upon UV light illumination with 30 mW cm 2 whereas the color reverted back to blue in the dark (Fig. 3B). Given that PW itself could be oxidized directly by oxygen, we also compared the performance of the device in the presence and absence of Pt. As shown in Fig. S3 (ESI†), it could be observed that the rate of recovery in the presence of Pt is superior to that in the absence of Pt although self-recovery can be observed in the absence of Pt. Furthermore, to make the UV detection more visual, we also recorded a video of the reproducible response to an ON–OFF light switch cycle with 30 mW cm 2 (Video S1 in the ESI†). It can be observed from the movie that the response time of the PB display to UV is fast, in which the blue can be changed into white within 30 s and can be recovered within 5 min. Apparently, the electrochromic performance of PB controlled by an ON–OFF light switch cycle is remarkable and stable. The intensity dependence of the absorbance change is shown in Fig. S4 (ESI†). The device was irradiated with 365 nm light at a power intensity ranging from 2 mW cm 2 to 40 mW cm 2. The results demonstrate that the absorbance change increased with light radiation, which makes this device a potential quantitative photodetector. In summary, we have successfully constructed a self-powered, visual and self-recovered UV photodetector by combining PB/ITO with Pt/TNT. With the aid of PB for electrochromic display, the existence of UV could be judged easily by naked eye. Significantly, the UV detector could also self-recover without UV light illumination. The facile operation, excellent reversibility and reproducibility make it a suitable candidate for photodetectors. It is also expected that our work may open new vistas for selfpowered UV detectors.
804 | Chem. Commun., 2014, 50, 802--804
This work was supported by the National Natural Science Foundation of China (Nos. 20935003 and 21075116) and the 973 Projects (2010CB933603, 2011CB911002).
Notes and references 1 Y. Taniyasu, M. Kasu and T. Makimoto, Nature, 2006, 441, 325. 2 F. Xia, T. Mueller, Y. M. Lin, A. Valdes-Garcia and P. Avouris, Nat. Nanotechnol., 2009, 4, 839. 3 S. Kim, Y. T. Lim, E. G. Soltesz, A. M. De Grand, J. Lee, A. Nakayama, J. A. Parker, T. Mihaljevic, R. G. Laurence, D. M. Dor, L. H. Cohn, M. G. Bawendi and J. V. Frangioni, Nat. Biotechnol., 2004, 22, 93. 4 B. Tian, X. Zheng, T. J. Kempa, Y. Fang, N. Yu, G. Yu, J. Huang and C. M. Lieber, Nature, 2007, 449, 885. 5 (a) Y. Q. Bie, Z. M. Liao, H. Z. Zhang, G. R. Li, Y. Ye, Y. B. Zhou, J. Xu, Z. X. Qin, L. Dai and D. P. Yu, Adv. Mater., 2011, 23, 649; (b) H. Gu, L. Bi, Y. Fu, N. Wang, S. Liu and Z. Tang, Chem. Sci., 2013, 4, 4371. 6 X. Fang, Y. Bando, M. Liao, T. Zhai, U. K. Gautam, L. Li, Y. Koide and D. Golberg, Adv. Funct. Mater., 2010, 20, 500. 7 H. Chen, L. Hu, X. Fang and L. Wu, Adv. Funct. Mater., 2012, 22, 1229. 8 L. Hu, L. Wu, M. Liao and X. Fang, Adv. Mater., 2011, 23, 1988. 9 X. Wang, M. Liao, Y. Zhong, J. Y. Zheng, W. Tian, T. Zhai, C. Zhi, Y. Ma, J. Yao, Y. Bando and D. Golberg, Adv. Mater., 2012, 24, 3421. 10 W. Jin, Y. Ye, L. Gan, B. Yu, P. Wu, Y. Dai, H. Meng, X. Guo and L. Dai, J. Mater. Chem., 2012, 22, 2863. 11 Z. Gao, W. Jin, Y. Zhou, Y. Dai, B. Yu, C. Liu, W. Xu, Y. Li, H. Peng, Z. Liu and L. Dai, Nanoscale, 2013, 5, 5576. 12 M. Chen, L. Hu, J. Xu, M. Liao, L. Wu and X. Fang, Small, 2011, 7, 2449. 13 Q. Yang, Y. Liu, Z. Li, Z. Yang, X. Wang and Z. L. Wang, Angew. Chem., Int. Ed., 2012, 51, 6443. 14 J. Henzie, M. H. Lee and T. W. Odom, Nat. Nanotechnol., 2007, 2, 549. 15 A. M. Prenen, J. C. A. H. van der Werf, C. W. M. Bastiaansen and D. J. Broer, Adv. Mater., 2009, 21, 1751. 16 J. Chen, C. Li, G. Eda, Y. Zhang, W. Lei, M. Chhowalla, W. I. Milne and W. Q. Deng, Chem. Commun., 2011, 47, 6084. 17 N. Yang, J. Zhai, D. Wang, Y. Chen and L. Jiang, ACS Nano, 2010, 4, 887. 18 (a) X. Li, C. Gao, H. Duan, B. Lu, X. Pan and E. Xie, Nano Energy, 2012, 1, 640; (b) X. Li, C. Gao, H. Duan, B. Lu, Y. Wang, L. Chen, Z. Zhang, X. Pan and E. Xie, Small, 2013, 9, 2005. 19 Z. L. Wang and W. Wu, Angew. Chem., Int. Ed., 2012, 51, 11700–11721. 20 (a) L. Jin, Y. Fang, L. Shang, Y. Liu, J. Li, L. Wang, P. Hu and S. Dong, Chem. Commun., 2013, 49, 243; (b) L. Bai, L. Jin, L. Han and S. Dong, Energy Environ. Sci., 2013, 6, 3015. 21 L. Han, L. Bai, C. Zhu, Y. Wang and S. Dong, Chem. Commun., 2012, 48, 6103. 22 L. Xing, J. Jia, Y. Wang, B. Zhang and S. Dong, Int. J. Hydrogen Energy, 2010, 35, 12169.
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Cite this: Chem. Commun., 2014, 50, 802
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Self-powered visual ultraviolet photodetector with Prussian blue electrochromic display† Lei Han, Lu Bai and Shaojun Dong*
Received 16th September 2013, Accepted 24th October 2013 DOI: 10.1039/c3cc47080f www.rsc.org/chemcomm
A novel self-powered ultraviolet (UV) photodetector was successfully constructed through combining Pt-modified TiO2 nanotubes and Prussian blue (PB)-modified ITO, in which the existence of UV could be judged easily by naked eye with the aid of PB for electrochromic display. More importantly, it could also self-recover without UV light illumination.
In the past decades, semiconductor-based photodetectors, one kind of optoelectronic device, have gained increasing attention owing to their potential applications in many aspects such as imaging techniques, chemical/biological sensing, optical communication and optoelectronic circuits.1–5 Generally there are two kinds of photodetector: photoconductor type and photodiode type.5–12 The former need to be driven by external power sources such as batteries and other energy storage/supply systems, which not only largely increase the system size but also greatly limit their mobility and independence for applications.13 In contrast, photodiode-type photodetectors such as p–n junctions and Schottky junctions can work without an external power supply, whereas their fabrication procedures require a fairly strict environment and sophisticated laboratory equipment with high operation costs.14,15 Thus it is still urgent to develop novel and simple routes to fabricate low-cost and high performance photodetectors. Photoelectrochemical cells (PECs) have been widely investigated as a new kind of green energy-conversion technology such as dye and quantum dot sensitized solar cells.16,17 Until recently, PECs have been proposed as a new type of self-powered photodetector due to their low-cost and simple manufacturing process.18,19 In these systems, F-doped tin oxide glass modified nanocrystalline TiO2 films were used as photoanodes. Upon light illumination with energy larger than the band gap, photogenerated electrons transfer from the valence band to the conduction band and then flow through an external circuit to the cathode. The photogenerated State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, University of the Chinese Academy of Sciences, Changchun 130022, Jilin, PR China. E-mail: [email protected] † Electronic supplementary information (ESI) available. See DOI: 10.1039/ c3cc47080f
802 | Chem. Commun., 2014, 50, 802--804
holes migrate to the electrode/electrolyte interface to oxidize electron donors in the electrolyte. It has been found that the performance of PEC-type self-powered photodetectors is much superior to that of photoconductivity-based photodetectors because their unique structure avoids the presence of a carrier depletion layer at the nanomaterial surface caused by surface trap states. In addition, Prussian blue (PB) is known to possess excellent electrochromic properties and a suitable redox reaction region, which make it a prominent candidate for electrochromic displays.20 Inspired by this, a novel self-powered and visual photodetector (SPVP) was successfully constructed by introducing PB into a PEC as one electrode and electrochromic display for the first time. Compared to previous PEC-type photodetectors, there are some advantages of our system. On the one hand, TiO2 nanotubes (TNTs) were chosen as the building blocks of the photodetector owing to their easy preparation and some distinct merits such as large surface-area and short electron diffusion length. On the other hand, whether UV exists or not could be observed directly by the color change of PB, where its original state is deep blue and the reduced state is transparent. The key to the successful operation of a SPVP is the rational selection of a semiconductor that can couple well with the electrochromic reaction. The principle of the selection is mainly based on the semiconductor band edge position versus the redox potential presented by the electrochromic reaction. Fig. 1 shows the general working principle of an SPVP based on a Pt-modified TiO2 nanotube photoanode (Pt/TNT) and a PB-modified ITO cathode (PB/ITO). Upon ultraviolet (UV) light illumination, a number of electron–hole pairs are generated (eqn (1)–(3)). Given that the TNTs possess suitable band structures,21 photogenerated holes could oxidize water to oxygen while photogenerated electrons flow through an external circuit to the cathode, where PB is reduced to Prussian white (PW) and the corresponding blue color becomes transparent. Thus we could judge the existence of UV through the color change of PB. It should be noted here that Pt/TNT could also be used as the cathode while PW reoxidizes in the dark. Among various noble metals, Pt possesses excellent electrocatalytic activity towards oxygen reduction, so we chose it to modify the TNT photoanode. When connected
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Fig. 1 General working principle of a self-powered, visual and selfrecovered photodetector.
with PW-modified ITO, the PW can be oxidized to PB whereas the electrons flow to the Pt/TNT cathode, which catalyzes oxygen reduction (eqn (4) and (5)). Based on the discussions above, a selfpowered, visual and self-recovered photodetector could be achieved. We first used an electrochemical anodic oxidation technique to prepare the TNT photoanode (Experimental section in ESI†).21 Then the Pt/TNT photoanode was synthesized by electrodepositing Pt nanoparticles (NPs) on the TNTs.22 As shown in Fig. S1A (ESI†), high density well-ordered and uniform nanotube structures could be observed. The diameter and wall thickness of these nanotubes were ca. 70 nm and 16 nm, respectively. Fig. S1B (ESI†) depicts an SEM image of the as-synthesized Pt/TNTs. It can be seen that Pt NPs of about 80 nm are randomly distributed on the surfaces of the TNTs. Fig. S2 (ESI†) reveals XRD patterns of the as-synthesized TNTs and Pt/TNT. For the TNTs, there are two diffraction peaks at about 2y = 25.41 and 48.11 corresponding to the (101) and (200) crystal faces of anatase TiO2 (JCPDS file: 89-4921), whereas the diffraction peaks at about 2y = 34.91 and 76.31 can be indexed to the crystal faces of rutile TiO2.21 In addition to these peaks, an additional two peaks at 46.41 and 67.81 were observed for Pt/TNT, which were ascribed to the (200) and (220) crystal faces of Pt (JCPDS file: 87-0646). These results demonstrated that Pt NPs were successfully deposited on the surfaces of the TNTs. Additionally, PB was electrodeposited on the ITO electrode as an electrochromic display layer. According to our previous reports,20 PB exhibits a broad absorption in the wavelength range of 500–800 nm. When applying a suitable negative bias, Fe(III) in PB was reduced to Fe(II) and the corresponding PB was converted to Prussian white (PW). Thus the absorbance decreased remarkably owing to the elimination of the intervalence charge transfer from Fe(III) to Fe(II). Meanwhile, the color changed from blue to transparent, indicating that PB could be used for electrochromic display. TiO2 + hn - e (TiO2) + h+(TiO2)
(1)
h+(TiO2) + 2H2O - O2 + 4H+
(2)
e (TiO2) + PB - PW
(3)
O2 + 4H+ + 4e - 2H2O
(4)
PW
e - PB
(5)
In order to validate the feasibility of the experiment design, we investigated the photoelectrochemical performance of Pt/TNT
This journal is © The Royal Society of Chemistry 2014
Fig. 2 (A) and (B) LSV collected from Pt-modified TiO2 nanotubes at a scan rate of 10 mV s 1 at applied potentials from 0.55 to 0.6 V vs. Ag/AgCl in 0.1 M PBS (pH = 6.0) containing 0.1 M KCl. (C) Cyclic voltammogram of PB/ITO in PBS at a scan rate of 10 mV s 1.
in a three-electrode cell with platinum foil as a counter electrode and Ag/AgCl (saturated KCl) as the reference electrode. Considering the stability of PB, we chose 0.1 M phosphate buffer solution (PBS) (pH = 6.0) containing 0.1 M KCl as the electrolyte throughout subsequent experiments. Fig. 2A shows the linear sweep voltammograms (LSV) recorded at the Pt/TNT electrode with and without UV light illumination from 0.55 V to 0.6 V at a scan rate of 10 mV s 1. There are two oxidation peaks between 0.55 V and 0.2 V, which were ascribed to hydrogen adsorption events at the Pt/TNT electrode, which further confirmed that Pt was successfully deposited on the surfaces of the TNTs. It can also be observed that there is an obviously enhanced oxidation photocurrent (0.4 mA cm 2) at 0 V vs. Ag/AgCl under UV light illumination compared to that in the dark, indicating a good photovoltaic performance. At the same time, we also investigated the Pt/TNT towards oxygen reduction through LSV. It can be seen from Fig. 2B that a large cathodic wave appears ( 0.09 mA cm 2) in air-saturated solution with the onset potential around 0.5 V vs. Ag/AgCl. As shown in Fig. 2C, the redox potential of PB lies around 0.21 V, which is just in the range from 0.1 V to 0.55 V. These results suggest that the as-prepared Pt/TNT electrode possesses good photoelectrocatalytic activity toward water oxidation at a low potential and electrocatalytic activity toward O2 reduction at a high potential. Therefore, it is reasonable to conclude that Pt/TNT could be used not only as a photoanode upon UV light illumination but also as a cathode in the dark to adjust the redox states of PB through electrons flowing from negative potential to a more positive potential (shown in Fig. 1). To demonstrate the self-powered and visual PEC-type photodetector concept, we combined PB/ITO with the dual functional Pt/TNT electrode to make a PEC. As shown in Fig. 3A, upon UV light illumination, decreased absorbance was observed because the reduction of Fe(III) in PB resulted in the elimination of the intervalence charge transfer from Fe(III) to Fe(II) causing its absorbance.20 In the dark, the absorbance returned to its
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Fig. 3 (A) Absorption response versus time during ten consecutive reproducible responses to ON–OFF light switch cycles with light intensity 10 mW cm 2. (B) The color change of the PB/ITO, (a): in the open circuit; (b): upon UV light illumination; (c): in the dark. Note: the absorbance of Prussian blue (PB) as baseline.
original state (Fig. 3A). In order to obtain clear information about the stability and responsiveness of the self-powered UV photodetector, ten consecutive reproducible responses to ON– OFF light switch cycles were performed. As shown in Fig. 3A, no obvious absorbance change was observed on periodically turning the UV light on and off with a power density of 10 mW cm 2 and the wavelength of 365 nm. What is more, the absorbance of PB decreased from 0 to 0.42 within 30 s and it could be recovered within 80 s. It can also be clearly seen that the color changed from blue to colorless upon UV light illumination with 30 mW cm 2 whereas the color reverted back to blue in the dark (Fig. 3B). Given that PW itself could be oxidized directly by oxygen, we also compared the performance of the device in the presence and absence of Pt. As shown in Fig. S3 (ESI†), it could be observed that the rate of recovery in the presence of Pt is superior to that in the absence of Pt although self-recovery can be observed in the absence of Pt. Furthermore, to make the UV detection more visual, we also recorded a video of the reproducible response to an ON–OFF light switch cycle with 30 mW cm 2 (Video S1 in the ESI†). It can be observed from the movie that the response time of the PB display to UV is fast, in which the blue can be changed into white within 30 s and can be recovered within 5 min. Apparently, the electrochromic performance of PB controlled by an ON–OFF light switch cycle is remarkable and stable. The intensity dependence of the absorbance change is shown in Fig. S4 (ESI†). The device was irradiated with 365 nm light at a power intensity ranging from 2 mW cm 2 to 40 mW cm 2. The results demonstrate that the absorbance change increased with light radiation, which makes this device a potential quantitative photodetector. In summary, we have successfully constructed a self-powered, visual and self-recovered UV photodetector by combining PB/ITO with Pt/TNT. With the aid of PB for electrochromic display, the existence of UV could be judged easily by naked eye. Significantly, the UV detector could also self-recover without UV light illumination. The facile operation, excellent reversibility and reproducibility make it a suitable candidate for photodetectors. It is also expected that our work may open new vistas for selfpowered UV detectors.
804 | Chem. Commun., 2014, 50, 802--804
This work was supported by the National Natural Science Foundation of China (Nos. 20935003 and 21075116) and the 973 Projects (2010CB933603, 2011CB911002).
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