Nitrogen-doped Carbon Nanodots for bioimaging and delivery of paclitaxel

Article abstract of DOI:10.1039/x0xx00000x

Carbon nanodots (CNDs) hold great potential in imaging and drug delivery applications. In this study, nitrogen-doped CNDs (NCNDs) were coupled to the anticancer agent paclitaxel (PTX) through a labile ester bond. NCNDs showed excellent cell viability and

Full text of DOI:10.1039/x0xx00000x

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Flexible high efficiency perovskite solar cells
Supporting Information
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
a,‡
a
Cristina Roldán-Carmona a,b, , Olga Malinkiewicz , Alejandra Soriano , Guillermo
Mínguez Espallargasa, Ana Garciac, Patrick Reineckec,d, Thomas Kroyerc, M. Ibrahim
Dare, Mohammad Khaja Nazeeruddine and Henk J. Bolinka*
‡
DOI: 10.1039/x0xx00000x
www.rsc.org/
Methods
Materials
Aqueous dispersions of poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS,
CLEVIOS P VP Al 4083) were obtained from Heraeus Holding GmbH and used as received. poly[N,N’-bis(4-
butylphenyl)-N,N’-bis(phenyl)benzidine] (poly-TPD) was purchased from ADS Dyesource. PbI2 was purchased
from Aldrich and used as is, CH3NH3I was prepared similar to a previously published method1, in brief: CH3NH3I,
was synthesized by reacting 21.6 ml methylamine (40%wt in water, Aldrich) and 30 ml hydroiodic acid (57 wt% in
water,Aldrich) in a 250 ml round-bottomed flask at 0 C for 2 h with stirring. The white precipitate was recovered
by evaporation at 50C for 1 h. The product, methylammonium iodide (CH3NH3I), was dissolved in ethanol, filtered
and recrystallized from diethyl ether, and dried at 60 C in a vacuum oven for 24 h.
Device preparation
Devices were prepared on cleaned AZO/Ag/AZO on PET substrates, by spincoating a thin layer of PEDOT:PSS
from the commercial aqueous dispersion (1200rpm 30sec and a short annealing at 150 C result in 70 nm
thickness). On top of this layer a thin film of polyTPD was deposited from a chlorobenzene solution (10 mg ml−1)
using spincoating. Then the substrates were transferred to a vacuum chamber integrated into an inert glovebox
(MBraun, <0.1 ppm O2 and <0.1 ppm H2O) and evacuated to a pressure of 1 × 10−6 mbar. The sublimation of the
perovskite was performed using a vacuum chamber of MBraun integrated in an inert glovebox (MBraun).
Temperature controlled evaporation sources from Creaphys fitted with ceramic crucibles were employed to sublime
the CH3NH3I and the PbI2. The sources are directed upwards with an angle of approximately 90  with respect to
the bottom of the evaporator. The substrates were placed at a distance of 20 cm from the top of the evaporation
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sources. Shutters are present at the evaporation sources and below the substrate holder. Three quartz microbalance
sensors are present in the chamber, two monitoring the rate of each evaporation source and a third one at the height
of the substrate holder. After the ceramic crucibles were loaded with the CH3NH3I and the PbI2 the chamber was
evacuated to a base pressure of 1*10-6 mbar. Fresh CH3NH3I was used for each evaporation. After the base pressure
was reached, the CH3NH3I crucible was heated to 70 C. At this temperature, all three quartz sensors gave a signal.
We were, however, unable to calibrate the sensor by measuring the thickness of a deposited CH3NH3I film.
Therefore, an alternative process was used. Upon stabilization of the sensor reading the crucible containing the PbI2
was heated. Only at PbI2 evaporation temperatures in excess of 200 C were dark brown films obtained. The film
thickness of the perovskite film was monitored using quartz sensor nr 3 (at the height of the substrate holder).
Perovskite films were prepared at different PbI2 evaporation temperatures, increasing with 10 degrees from the
predetermined 200 C. In this way the optimum films were obtained at an evaporation temperature of the PbI2
crucible of 250 C. The PCBM layer was deposited using a chlorobenzene solution of 10 mg ml−1 in ambient
conditions using a meniscus coater and a coating speed of 10 mm/ second. The device was completed by the
thermal evaporation of the top metal electrode under a base pressure of 2 × 10−6 mbar to a thickness of 100nm. The
solar cells (active area of 0.12 cm2) were characterized inside the inert glovebox.
Characterization
GIXRD data were collected at room temperature in the 2θ range 5–50 º on an Empyrean PANalytical powder
diffractometer, using Cu Kα1 radiation. Typically four repeated measurements were collected and merged into a
single diffractogram. Pawley refinements2, were performed using the TOPAS computer program3 and revealed an
excellent fit to a one-phase model with a tetragonal cell (a = 8.80(2), c = 12.57(2) Å) and space group I4/mcm.
Additional peaks corresponding to the ITO substrate were also observed.
Scanning Electron Microscopy
Film thickness was investigated using a high-resolution scanning electron microscope (MERLIN, Zeiss) and
micrographs were acquired using an in-lens secondary electron detector. Prior to analysis, the sample was coated
with 12 nm carbon to minimize the charging effect.
Device characterization
Solar cells were illuminated by a white light halogen lamp in combination with interference filters for the EQE and
J-V measurements (MiniSun simulator by ECN the Netherlands). A black mask was used to limit the active area of
the device. Before each measurement, the exact light intensity was determined using a calibrated Si reference
diode. An estimation of the short-circuit current density (Jsc) under standard test conditions was calculated by
convolving the EQE spectrum with the AM1.5G reference spectrum, using the premise of a linear dependence of Jsc
on light intensity. Current-voltage (J-V) characteristics were measured using a Keithley 2400 source measure unit.
All characterization was done in a nitrogen filled glove box (<0.1 ppm O2 and <0.1 ppm H2O) without exposure to
ambient atmosphere.
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Notes and references
a Instituto de Ciencia Molecular, Universidad de Valencia, C/ Catedrático J. Beltrán 2, 46980 Paterna (Valencia), Spain. henk.bolink@uv.es
b Department of Physical Chemistry and Applied Thermodynamics, Campus Rabanales, Ed. C3, University of Cordoba, 14014, Spain.
c Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstrasse 2, 79110 Freiburg, Germany.
d
Freiburg Materials Research Center (FMF), Stefan-Meier-Strasse 21, 79104 Freiburg, Germany
e Laboratory of Photonics and Interfaces, Swiss Federal Institute of Technology (EPFL), Station 6, Lausanne, CH 1015, Switzerland.
‡
These authors contributed equally to this work.
1. L. Etgar, P. Gao, Z. Xue, Q. Peng, A. K. Chandiran, B. Liu, M. K. Nazeeruddin and M. Grätzel, Journal of the American Chemical Society, 2012,
134, 17396-17399.
2. G. S. Pawley, J. Appl. Cryst., 1981, 14, 357-361.
3. Coelho, A. A. TOPAS-Academic, Version 4.1, 2007, see: http:// www.topas-academic.net.
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