Efficient Solid-State Electrochemiluminescence from High-Quality

Subscriber access provided by UNIV OF NEWCASTLE

Letter

Efficient Solid-State Electrochemiluminescence from High-Quality Perovskite Quantum Dot Films Jingjing Xue, Ziyi Zhang, Fenfen Zheng, Qin Xu, Jinchun Xu, Guizheng Zou, Lingling Li, and Jun-Jie Zhu Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.7b02291 • Publication Date (Web): 21 Jul 2017 Downloaded from http://pubs.acs.org on July 21, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Analytical Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry

Efficient Solid-State Electrochemiluminescence from High-Quality Perovskite Quantum Dot Films Jingjing Xue,† Ziyi Zhang,† Fenfen Zheng,† Qin Xu,‡ Jinchun Xu,† Guizheng Zou,§ Lingling Li,*,† and Jun-Jie Zhu*,† †

State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, Jiangsu, China, 210093 ‡ College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, China § School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China ABSTRACT: Halide perovskite materials have emerged as a new class of revolutionary photovoltaic and optoelectronic nanomaterials. However, the study on electrochemiluminescence (ECL) from halide perovskite nanomaterials is still in its infancy due to their instability, sensitivity, and difficulties in purification and film formation. Here we propose a scraping coating method for the fabrication of high-quality halide perovskite quntum dot (QD) film on electrode, which shows dense and uniform packing with minimum grain size. Taking CsPbBr3 QDs as model materials, highly efficient ECL can be obtained from such perovskite QD film with anhydrous ethyl acetate as both electrolyte and co-reactant. The CsPbBr3 QD film displays intense and stable ECL with ultranarrow emission spectrum bandwidth (24 nm). The CsPbBr3 QD film shows an extremely high ECL efficiency which is up to 5 times relative to the standard Ru(bpy)32+/ tri-n-propylamine system. This approach is universal and also applies to hybrid organicinorganic halide perovskite QDs. This work not only extends the properties and applications of halide perovskite materials, but also provides a new method for the in-depth study on the structure and properties of this kind of materials.

Lead halide perovskite materials [APbX3, where A = CH3NH3+ (methylammonium or MA+), HC(NH2)2+ (formamidinium or FA+), or Cs+; X= Br-, I-, or Cl-] are currently the focus of a considerable research effort owing to their fascinating optical and electrical properties and promising applications in various fields.1-6 However, up to now, most researches and applications of this kind of materials were confined to optoelectronic devices, and higher performance for practical applications remains a challenge.7 As a promising emitter, the origin of photoluminescence in halide perovskite is also unclear at some stages.8 Therefore, better understanding its structure, exploring its properties, and excavating its potential applications are still attractions to scientists. Since Bard reported the first Si quantum dots (QDs) based electrochemiluminescence (ECL), a wide range of QDs have been applied to ECL and further used for theoretical analysis of surface states of QDs and a variety of sensors.10-13 Nevertheless, the ECL efficiency of most QDs is very low, and seeking for novel ECL emitters with high efficiency are a challenging and persistent theme in the realm of ECL. Considering the high photoelectric conversion efficiency of halide perovskite solar cells,14-15 and high fluorescence quantum yield (QY) of halide perovskite QDs (up to 90%),16 it is highly possible that halide perovskite materials could be a promising candidate for ECL system with high efficiency. Besides, halide perovskite QDs display narrow spectral width and defect-tolerant photophysics,17-18 which distinguish themselves from traditional colloidal semiconductor QDs. Thus exploring ECL of halide perovskite QDs will be a subject worthy of study. However, the ionic nature of halide perovskites makes them unstable (prone to dissolution) in common polar solvents and

insoluble in mildly polar solvent.19 As a result, investigation on solid-state ECL from halide perovskite QD film seems to be more feasible than that from their colloidal dispersions. High-quality perovskite QD film with uniform and dense morphology and minimum grain size is the necessary prerequisite for excellent electrical properties and charge transporting capabilities.19-20 Nevertheless, the necessity of organic capping ligands (such as oleylamine and oleic acid) complicated the film formation as a result of a compromise between dispersibility and charge transport capabilities.21-22 Therefore, it still remains challenging to prepare high-quality solutionprocessed perovskite QD film via appropriate ligand density control. The study on ECL from halide perovskite QDs is still in its infancy. Present works on annihilation and co-reactant ECL of halide perovskite QD film were realized by simple drop casting method.23, 24 However, the morphology and stability of perovskite QD film on electrode under ECL conditions, including the applied potentials and selected electrolyte solution with appropriate polarity, are still issues yet to be studied. In this work, we developed a novel approach for forming highquality lead halide perovskite QD film with efficient and stable ECL by using anhydrous ethyl acetate (EA) as both antisolvent to purify the perovskite QDs and co-reactant in ECL process. The high ECL efficiency of CsPbBr3 QD film (5 times in reference to the standard Ru(bpy)32+/tri-npropylamine system) and high colour purity (narrow emission linewidth of 24 nm) outperformed those from both traditional ECL reagents and classical chalcogenide QDs. This approach also applied to hybrid organic-inorganic (MAPbBr3 and FAPbBr3) halide perovskite QDs.

ACS Paragon Plus Environment

Analytical Chemistry

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

CsPbBr3 QDs with a schematic cubic perovskite crystal structure as shown in Figure 1a were synthesized according to the literature and purified once using EA as antisolvent to form long-term colloidally stable solutions in hexane.16 Further purifications with EA would cause inevitable aggregation and precipitate of CsPbBr3 QDs due to the serious loss of capping ligands. The product displayed distinct absorption peak and emitted strong green fluorescence (FL) at 509 nm with a narrow full width at half maximum (FWHM) of 20 nm (Figure 1b) and high QY of 88.4% with quinine sulfate as the standard reference. Transmission electron microscopy (TEM) image in Figure 1c clearly shows the highly monodisperse cubic-shaped CsPbBr3 QDs with an average size of 8 nm. The CsPbBr3 QD film was fabricated by a scraping coating method on glassy carbon electrode (GCE). The CsPbBr3 QDs in hexane were dried under vacuum to obtain a thick slurry with a certain degree of viscosity due to the residual octadecene (ODE).19 Then the CsPbBr3 QD slurry was scraped onto the freshly cleaned GCE and swiftly dipped into EA solution to produce a firm CsPbBr3 QD film. The film assembled from CsPbBr3 QDs in hexane via drop coating was also fabricated for comparison. The scanning electron microscopy (SEM) image in Figure 1d presented that the drop-coated film was discrete in morphology with large grain size, probably as a result of the residual organic chemicals in one-time-purified CsPbBr3 QDs.22 Meanwhile the scrape-coated CsPbBr3 QD film without EA treatment showed denser coverage, but larger grain size could also be obviously observed (Figure 1e). In sharp contrast, after dip-coating in EA for several times, the scrape-coated CsPbBr3 QD film exhibited significantly reduced grain size while maintaining dense packing (Figure 1f). It was speculated that the purification steps after film formation could get rid of the deteriorated stability and agglomeration issues encountered by perovskite QD solution. In the meantime, EA treatment could remove unadsorbed CsPbBr3 QDs and large grains, leading to purified and dense CsPbBr3 QD film with minimum grain size. The high quality of the scrape-coated film after dip-coating in EA was further revealed by the negligible redshift of FL peaks in comparison with pristine CsPbBr3 QDs (Figure S1).

Figure 1. (a) The schematic cubic crystal structure of CsPbBr3 QDs. (b) Fluorescence and UV–vis absorbance spectra of CsPbBr3 QDs dispersed in hexane. The inset shows photographs of CsPbBr3 QDs under visible and UV light. (c) HRTEM image of CsPbBr3 QDs. (d) SEM image of CsPbBr3 QD film deposited with hexane solvent. (e, f) SEM images of CsPbBr3 QD film via scraping coating before and after EA treatment, respectively.

The electrochemistry of CsPbBr3 QD film was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), and representative traces are shown in Figure S2

Page 2 of 5

and Figure 2a. EA containing 0.05 M tetra-n-butylammonium hexafluorophosphate (TBAPF6) served as the electrolyte solution. As the potential was scanned from zero to 1.0 V at the scan rate of 0.2 V/s, ECL onset and peak potentials of 0.7 V and 0.9 V respectively aligned well with the anodic current peak in the CV curve. No ECL signal was observed from bare electrode in the same solution, indicating that the ECL originated from CsPbBr3 QDs. DPV better displays the redox behavior due to suppression of the background current. During anodic scanning of the applied potential (red curve, Figure 2a), an anodic peak was observed around 0.9 V, which was slightly less positive than the ECL peak potential. So, obviously, the ECL signal was attributed to the electrogenerated oxidized species of CsPbBr3 QDs at around 0.9 V. The CsPbBr3 QD film kept almost intact even after several hours of electrochemical testing, and the ECL intensity was unchanged under consecutive CV scanning (inset in Figure 2a), indicating the high quality of CsPbBr3 QD film.

Figure 2. (a) ECL-potential curve of CsPbBr3 film in TBAPF6anhydrous ethyl acetate electrolyte with a potential window between 0.0 V and 1.0 V, and its corresponding DPV curve. Insert: corresponding ECL-time curve of CsPbBr3 QD film. (b) Schematic illustration of proposed ECL mechanism of CsPbBr3 QDs/EA system. (c) Fluorescence and ECL spectra of CsPbBr3 QD film. The ECL spectrum was obtained in the potential range of 0 to 1.0 V.

While exploring ECL mechanism of CsPbBr3 QDs, we speculated that there might be another species which contributed electrons to the electrogenerated cation radicals of CsPbBr3 QDs to form the excited states. The reductant could come from supporting electrolyte, TBAPF6, or EA solvent. When tetra-n-butylammonium perchlorate (TBAP) or tetra-nbutylammonium tetrafluoroborate (TBABF4) substituted TBAPF6 as the supporting electrolyte, similar ECL performance was observed. However, in a different solvent, 1-butyl3-methylimidazolium tetrafluoroborate [(BMIm)BF4] ionic liquid, no ECL signal was observed under the same condition. In addition, when EA was added to the ionic liquid system, the ECL signal emerged and increased as the amount of EA increased, and finally reached a plateau (Figure S4). These results suggested that EA might act as the co-reactant. Rubinstein and Bard once revealed that CH3CO• can play a role as an electron provider to reduce Ru(bpy)33+.25 Accordingly, we propose CH3CO• electrogenerated from EA as a reductant in our system. The possible mechanism is described below. CsPbBr e → CsPbBr • (1) CH COOC H e → CH CO•  products

ACS Paragon Plus Environment

(2)

Page 3 of 5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry

CsPbBr •  CH CO• → CsPbBr ∗  products

(3)

CsPbBr ∗ → CsPbBr  

(4)

During positive scanning CsPbBr3 and EA are oxidized to generate [CsPbBr3]+•and CH3CO• respectively. Then the strong reducing intermediate radical CH3CO• combines with [CsPbBr3]+ • to yield the excited states, [CsPbBr3]*, which finally relaxes to the ground state via a radiative pathway by emitting a photon (Figure 2b). When the potential window was more positive, although the ECL still could be observed, the signal became unstable and kept decreasing as time went by. The decreasing rate increased as the potential window became wider (Figure S5). Additionally, when the more positive potential window was changed back to 0-1 V again, the weakened ECL signal could not recover (Figure S5D). The decrease in ECL intensity at more positive potentials was likely caused by the chemical stability of the CsPbBr3 QDs. CsPbBr3 QDs might be over-oxidized or even destroyed, and such reaction was not reversible, resulting in the decrease in ECL intensity at more positive potential. To investigate the electrochemistry of CsPbBr3 QDs in the cases mentioned above, DPVs with more positive final potential was taken. As is shown in Figure 3a, besides the peak around 0.9 V, another two anodic peaks were observed at about 1.1 V and 1.4 V, which is consistent with previous report,23 confirming the existence of over-oxidized products under more positive potential. What’ more, the peak around 0.9 V disappeared when the potential window was more positive than 1.2 V (Figure S6), suggesting the irreversibility of this reaction.

Figure 3. (a) DPV of CsPbBr3 QD film with the starting potential of 0.0 V and ending potential of 1.6 V. XPS of (b) Pb 4f (c) Br 3d for CsPbBr3 QD film electrochemically oxidized under different potential.

It is informative to compare the ECL spectrum with FL spectrum in order to identify the excited state involved in the ECL processes. As shown in Figure 2c, the accumulated ECL spectrum obtained in the potential range of 0 to 1.0 V shows a peak wavelength of 515 nm, which is in good agreement with the FL peak wavelength. The ECL spectra of CsPbBr3 QDs revealed similar peak wavelengths with potential window from 0 to 1.2 V and 0 to 1.5 V as well (Figure S7). This similarity in the peak wavelength between ECL and FL spectra suggested that the ECL and FL emission have similar mecha-

nisms, namely radiative electronic relaxation of the [CsPbBr3]* excited state across intrinsic band gap.26,27 Besides, it is noteworthy that the ECL spectrum exhibits high color purity with FWHM of 24 nm. This ultra-narrow ECL spectral width is superior to most nanomaterials obtained even after surface modifications, showing great potential for multiplexed sensing as well as high-definition ECL displays. Previous reports have presented the electronic structure of CsPbBr3, where the valence band maximum (VBM) is a mixture of Pb 6s and Br 4p states, whereas the conduction band minimum (CBM) is derived from Pb 6p states.18, 28 Consequently X-ray photoelectron spectroscopy (XPS) determinations of Pb and Br elements were further performed to get deep insight into the ECL mechanism of CsPbBr3 QDs, as shown in Figure 3b and Figure 3c, respectively. The main peaks of Pb 4f in the spectra of CsPbBr3 QD film prior to electrochemical reactions had binding energy positions of 142.7 eV and 137.8 eV (shown as blank sample in Figure 3b). When CsPbBr3 QD film were electrochemically oxidized under 1 V, the two main peaks shifted to higher binding energy of 143.0 eV and 138.0 eV, respectively, indicating the higher oxidation states of Pb.29-31 Differently, the peak of Br 3d with and without the electrochemical oxidization under 1 V remained the same position (Figure 3c). As a result, the electronic structure of CsPbBr3 QDs was almost unchanged, and the ECL intensity kept stable. On the other hand, the peaks of Pb 4f further shifted to higher binding energy positions with the applied potential increasing to 1.2 V and 1.5 V. As for Br 3d spectra, different from the case under 1.0 V, CsPbBr3 QDs oxidized under 1.2 V and 1.5 V had obvious peak shifts of 0.3 eV and 0.7 eV respectively. It was speculated that the oxidization of Br element and the over-oxidization of Pb element destroyed the electronic structure of CsPbBr3 QDs, leading to the irreversible decrease of ECL signal as discussed above. The ECL efficiency, defined as the ratio of the number of protons emitted to electrons transferred during the chemiluminescent process, was calculated versus that of Ru(bpy)32+/tri-npropylamine system at a potential scan rate of 100 mV/s (Supporting information).32 It is exciting to note that a high ECL efficiency of 5 times relative to Ru(bpy)32+/tri-n-propylamine system was obtained, which is the highest among the reported semiconductor nanocrystals.33-35 This exceptional ECL efficiency probably arises from the high photoelectric conversion efficiency and high fluorescence QY (88.4%) of CsPbBr3 QDs, which was substantially higher than the previously reported QY of Ru(bpy)32+ (~ 5%).36 Moreover, the purified surface of CsPbBr3 QDs after EA dip-coating and uniform film morphology with minimum grain size, which were indicative of the removal of insulating capping ligands, boosted charge injection and transport capabilities, and reduced non-radiative recombination at grain boundaries respectively, might contribute significantly to the high ECL efficiency as well. To test the universality of ECL from the scrape-coated perovskite QD film and the influence of component on ECL behavior, we attempted to use this strategy to generate ECL from hybrid organic-inorganic perovskite QDs. MAPbBr3 and FAPbBr3 QDs with nearly the same band gaps with that of CsPbBr3 QDs were synthesized (Figure S10 and S11). In comparison with CsPbBr3 QD film, similar ECL properties were observed from both MAPbBr3 and FAPbBr3 QD film (Figure S12 and S13). The results suggested that the all-inorganic and organic-inorganic halide perovskite QDs had similar electronic structures, which was supported by previous report.28, 37 It is

ACS Paragon Plus Environment

Analytical Chemistry

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

noteworthy that the ECL intensity of organic-inorganic perovskite films, especially MAPbBr3 QD film, are much weaker than that of CsPbBr3 QDs. This is consistent with the relative stability of these three types of perovskite.20,38 In summary, ECL and the corresponding electrochemical properties of halide perovskite QD film fabricated via a novel scraping coating method were reported. Ethyl acetate played multiple roles in this work, including antisolvent for purification of the perovskite QDs, electrolyte in electrochemical detection and co-reactant of perovskite QD ECL. The good quality of the proposed halide perovskite QD film ensured the highly efficient ECL with ultra-high color purity, thus making halide perovskite QDs as a promising ECL nanoemitter for broad applications ranging from multiplexed sensing, imaging, to high-definition ECL displays. Considering the values of ECL in theoretical analysis of structures of nanomaterials, we hope that these initial observations can be developed into a powerful tool in further understanding the structure and properties of halide perovskite materials. The sensitivity of ECL to QD surface chemistry or surface ligand might provide us a guide for exploring appropriate stabilizer to enable halide perovskite stable in much more solvents, thus solving a challenging problem restricting the application of halide perovskite materials.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Experiment details and additional UV-Vis, DPV, and ECL data. (PDF)

AUTHOR INFORMATION Corresponding Author *[email protected] *[email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT We gratefully appreciate financial support from National Natural Science Foundation of China (21335004, 21427807, 21427808, 21405078, and 21675140).

REFERENCES (1) Green, M. A.; Ho-Baillie, A.; Snaith, H. J. Nat. Photonics 2014, 8, 506-514. (2) Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Science 2012, 338, 643-647. (3) Chen, Q.; Zhou, H.; Hong, Z.; Luo, S.; Duan, H.; Wang, H.; Liu, Y.; Li, G.; Yang, Y. J. Am. Chem. Soc. 2014, 136, 622-625. (4) Zhou, H.; Chen, Q.; Li, G.; Luo, S.; Song, T.; Duan, H. S.; Hong, Z.; You, J.; Liu, Y.; Yang, Y. Science 2014, 345, 542-546. (5) Fu, A.; Yang, P. Nat. Mater. 2015, 14, 557-558. (6) Zhu, H. M.; Fu, Y. P.; Meng, F.; Wu, X. X.; Gong, Z. Z.; Ding, Q.; Gustafsson, M. V.; Trinh, M. T.; Jin, S. Zhu, X. Y. Nat. Mater. 2015, 14, 636-643. (7) Zhao, Y.; Zhu, K. Chem. Soc. Rev. 2016, 45, 655-689. (8) Constantinos C. S.; Mercouri G. K. Acc. Chem. Res. 2015, 48, 2791-2802. (9) Ding, Z. F.; Quinn, B. M.; Haram, S. K.; Pell,L. E.; Korgel, B. A.; Bard, A. J. Science 2002, 296, 1293-1297.

Page 4 of 5

(10) Bae, Y.; Myung, N.; Bard, A. J. Nano Lett. 2004, 4, 11531161. (11) Myung, N.; Lu, X. M.; Johnston, K. P.; Bard, A. J. Nano Lett. 2004, 4, 183-185. (12) Cheng, L.; Liu, X.; Lei, J.; Ju, H. Anal. Chem. 2010, 82, 33593364. (13) Liu, Z. Y.; Qi, W. J.; Xu, G. B. Chem. Soc. Rev. 2015, 44, 3117-3142. (14) Nie, W.; Tsai, H.; Asadpour, R.; Blancon, J. C.; Neukirch, A. J.; Gupta, G.; Crochet, J. J.; Chhowalla, M.; Tretiak, S.; Alam, M. A.; Wang, H.; Mohite, A. D. Science 2015, 347, 522-525. (15) Jeon, N. J.; Noh, J. H.; Yang, W. S.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I. Nature 2015, 517, 476-480. (16) Loredana, P.; Sergii, Y.; Maryna, I. B.; Franziska, K.; Riccarda, C.; Christopher, H. H.; Ruo, X. Y.; Aron, Walsh.; Maksym, V. K. Nano Lett. 2015, 15, 3692-3696. (17) Dirin, D. N.; Protesescu, L.; Trummer, D.; Kochetygov, I. V.; Yakunin, S.; Krumeich, F.; Stadie, N. P.; Kovalenko, M. V. Nano Lett. 2016, 16, 5866-5874. (18) Gonzalez-Carrero, S.; Galian, R. E.; Perez-Prieto, J. Opt. Express 2016, 24, A285. (19) Li, J.; Xu, L.; Wang, T.; Song, J.; Chen, J.; Xue, J.; Dong, Y.; Cai, B.; Shan, Q.; Han, B.; Zeng, H. Adv. Mater. 2017, 29, 1603885. (20) Zhang, L.; Yang, X.; Jiang, Q.; Wang, P.; Yin, Z.; Zhang, X.; Tan, H.; Yang, Y.; Wei, M.; Sutherland, B. R.; Sargent, E. H.; You, J. Nat. Commun. 2017, 8, 15640. (21) Ling, Y.; Tian, Y.; Wang, X.; Wang, J. C.; Knox, J. M.; PerezOrive, F.; Du, Y.; Tan, L.; Hanson, K.; Ma, B.; Gao, H. Adv. Mater. 2016, 28, 8983-8989. (22) Kim, Y.; Yassitepe, E.; Voznyy, O.; Comin, R.; Walters, G.; Gong, X.; Kanjanaboos, P.; Nogueira, A. F.; Sargent, E. H. ACS Appl. Mater. Interfaces 2015, 7, 25007-25013. (23) Huang, Y.; Fang, M.; Zou, G.; Zhang, B.; Wang, H. Nanoscale 2016, 8, 18734-18739. (24) Tan, X,; Zhang, B.; Zou, G. J. Am. Chem. Soc. 2017, 139, 8772-8776. (25) Rubinstein I.; Bard, A. J. J. Am. Chem. Soc. 1981, 103, 512516. (26) Swanick, K. N.; Hesari, M.; Workentin, M. S.; Ding, Z. J. Am. Chem. Soc. 2012, 134, 15205-15208. (27) Hesari, M.; Workentin, M. S.; Ding, Z. ACS Nano 2014, 8, 8543-8553. (28) Jishi, R. A.; Ta, O. B.; Sharif, A. A. J. Phys. Chem. C 2014, 118, 28344- 28349. (29) Sadoughi, G.; Starr, D. E.; Handick, E.; Stranks, S. D.; Gorgoi, M.; Wilks, R. G.; Bär, M.; Snaith, H. J. ACS Appl. Mater. Interfaces 2015, 7, 13440-13444. (30) Qiu, W.; Buffière, M.; Brammertz, G.; Paetzold, U. W.; Froyen, L.; Heremans, P.; Cheyns, D. Org. Electron. 2015, 26, 30-35. (31) Guo, X.; McCleese, C.; Kolodziej, C.; Samia, A. C. S.; Zhao, Y.; Burda, C. Dalton Trans. 2016, 45, 3806-3813. (32) Perez-Tejeda, P.; Prado-Gotor, R.; Grueso, E. M. Inorg. Chem. 2012, 51, 10825-18031. (33) Wang, T.; Wang, D.; Padelford, J. W.; Jiang, J.; Wang, G. J. Am. Chem. Soc. 2016, 138, 6380-6383. (34) Wang, F.; Lin, J.; Zhao, T.; Hu, D.; Wu, T.; Liu, Y. J. Am. Chem. Soc. 2016, 138, 7718-7724. (35) Hesari, M.; Swanick, K. N.; Lu, J.-S.; Whyte, R.; Wang, S.; Ding, Z. J. Am. Chem. Soc. 2015, 137, 11266-11269. (36) Li, C.; Lin, J.; Yang, X.; Wan, J. J. Organomet. Chem. 2011, 696, 2445-2450. (37) Endres, J.; Egger, D. A.; Kulbak, M.; Kerner, R. A.; Zhao, L.; Silver, S. H.; Hodes, G.; Rand, B. P.; Cahen, D.; Kronik, L.; Kahn, A. J. Phys. Chem. Lett. 2016, 7, 2722-2729. (38) Levchuk, I.; Osvet, A.; Tang, X.; Brandl, M.; Perea, J. D.; Hoegl, F.; Matt, G. J.; Hock, R.; Batentschuk, M.; Brabec, C. J. Nano Lett. 2017, 17, 2765-2770.

ACS Paragon Plus Environment

Page 5 of 5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry

Table of Contents (TOC)

ACS Paragon Plus Environment