Cesium lead halide perovskite nanocrystals for ultraviolet and blue light blocking

Article abstract of DOI:10.1016/j.cclet.2018.12.028

Using cesium lead halide perovskite nanocrystals, CsPb(Cl/Br)₃, as a light absorber, we report a highly effective UV and blue light blocking film. The CsPb(Cl/Br)₃ nanocrystals are well dispersed in the ethyl cellulose (EC) matrix to compose a UV and blue light shielding film, and the absorption edge of the film is tunable by adjusting Cl to Br ratio using anion exchange. The CsPbCl₂Br-EC film exhibits a transmittance of 5% at 459 nm, 90% at 478 nm and 95% in the range of 500–800 nm, which makes it excellent for UV and blue light shielding. In addition, the as-prepared EC-CsPb(Cl/Br)₃ film shows excellent photostability under UV irradiation. Results demonstrate that this EC-CsPb(Cl/Br)₃ based materials with sharp absorbance edges, tunable blocking wavelength, and high photostability can be useful for the applications in UV and blue light blocking and optical filters

Full text of DOI:10.1016/j.cclet.2018.12.028

Accepted Manuscript
Title: Cesium lead halide perovskite nanocrystals for
ultraviolet and blue light blocking
Authors: Guihua Huang, Yipeng Huang, Wei Xu, Qiuhong
Yao, Xiaofang Liu, Caifeng Ding, Xi Chen
PII:
DOI:
Reference:
S1001-8417(18)30498-4
https://doi.org/10.1016/j.cclet.2018.12.028
CCLET 4765
To appear in:
Chinese Chemical Letters
Received date:
Revised date:
Accepted date:
22 October 2018
24 December 2018
25 December 2018
Please cite this article as: Huang G, Huang Y, Xu W, Yao Q, Liu X, Ding C, Chen
X, Cesium lead halide perovskite nanocrystals for ultraviolet and blue light blocking,
Chinese Chemical Letters (2018), https://doi.org/10.1016/j.cclet.2018.12.028
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Communication
Cesium lead halide perovskite nanocrystals for ultraviolet and blue light blocking
a
b
b
a
c
d
b, *
Guihua Huang , Yipeng Huang , Wei Xu , Qiuhong Yao , Xiaofang Liu , Caifeng Ding , Xi Chen
a
Institute of Analytical Technology and Smart Instruments, College of Environment and Public Health, Xiamen Huaxia University, Xiamen 361024, China
State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China
b
c
Department of Anesthesiology, Xiamen Maternal and Children Hospital, Xiamen 361003, China
d
Key Laboratory of Sensor Analysis of Tumor Marker, Ministry of Education, College of Chemistry and Molecular Engineering, Qingdao University of Science
and Technology, Qingdao 266042, China

Corresponding author.
E-mail address: xichen@xmu.edu.cn (X. Chen).
Graphical abstract
High efficiency UV and blue light blocking film with tunable blocking range has been achieved using ethyl cellulose-
CsPb(Cl/Br) composites.
3
ARTICLE INFO
ABSTRACT
Article history:
Received
Using cesium lead halide perovskite nanocrystals, CsPb(Cl/Br)
highly effective UV and blue light blocking film. The CsPb(Cl/Br)
3
, as a light absorber, we report a
nanocrystals are well
3
Received in revised form
Accepted
dispersed in the ethyl cellulose (EC) matrix to compose a UV and blue light shielding film, and
the absorption edge of the film is tunable by adjusting Cl to Br ratio using anion exchange. The
Available online
CsPbCl
range of 500-800 nm, which makes it excellent for UV and blue light shielding. In addition, the
as-prepared EC-CsPb(Cl/Br) film shows excellent photostability under UV irradiation. Results
demonstrate that this EC-CsPb(Cl/Br) based materials with sharp absorbance edges, tunable
blocking wavelength, and high photostability can be useful for the applications in UV and blue
light blocking and optical filters.
2
Br-EC film exhibits a transmittance of 5% at 459 nm, 90% at 478 nm and 95% in the
Keywords:
Perovskite nanocrystals
UV blocking
Blue light blocking
Cesium lead halide nanocrystals
Tunable adsorption edge
3
3
Direct exposure to ultraviolet (UV) light is closely related to various harmful effects [1-3], ranging from skin injures to cancer
originated from DNA damage. Recent years, some studies reported that blue light are also detrimental to humans [4,5], for example,
the blue light could cause photochemical lesions to human retinal within the intensity range of the natural light [6]. Furthermore, blue
light is responsible for the solar retinitis and may play a role in age-related macular degeneration. Importantly, the harmful effects of
blue lights generated from the electronic display devices should also be careful [7]. Thus, the development of new UV and blue light
shielding materials has been received much attention [8].
In the past few years, there has been an increased awareness of the importance to develop UV shielding materials. A variety of
materials have been used to prevent UV lesions. Organic molecules like avobenzone or oxybenzone have been used as a UV absorber
for many years, but the self-degradation limits their usage time. Inorganic materials such as zinc oxide (ZnO) and titanium oxide (TiO
2
)
have been used intensively for UV shielding [9-12]. However, photocatalytic properties and self-degradations of the ZnO and TiO
2
based absorbers also hindered their applications [13,14]. Other materials, e.g., graphene oxide-poly(vinyl alcohol) composite film and
lanthanide complex functionalized cellulose nanopaper were also reported for UV shielding [15,16]. Whereas, the excellent UV-
filtering capability of these films was obtained by sacrificing the visible light transmittance. Therefore, fabricating UV and blue light
blocking materials with good photostability and high transparency to the rest of visible light still remains a challenge and is urgently
needed to be developed. Recently, because of the outstanding performance in photovoltaic applications, lead halide perovskite APbX
3
+
+
+
−
−
−
(where A = CH
3
NH
3
, (NH ) CH and Cs , X = Cl , Br and I ) has become the most noticeable materials [17-22]. These perovskite
2
2

nanocrystals exhibit intriguing features [23], such as easy tunable band gap, sharp optical absorption edges and high quantum
efficiency with narrow emission spectra. These nanocrystals have been studied extensively for various optical applications, especially
light emitting diodes and lasers [24-27]. Post modification of perovskite nanocrystals by anion exchange enables the absorbance band
gap tuned from ultraviolet to near infrared spectra [28,29]. In addition, the perovskite nanocrystals show large absorption range, which
offers the great potential for UV and blue light shielding applications. Although the tunable absorption-band edge of perovskite
nanocrystals has already been realized, there have not been reports on developing UV and blue light blocking material with tunable
absorption-band edge.
Herein, we aim to the development of a simple and easy way to fabricate UV and blue light blocking material by mixing pervoskite
nanocrystals and ethyl cellulose (EC). In this study, EC was used as a host material for the CsPb(Cl/Br) pervoskite nanocrystals. By
3
tuning the ratio of Br to Cl, the blocked wavelength range could be easily controlled. Using the sharp absorption edges, the material
possesses excellent light blocking ability in the range of 200-460 nm and maintains high transparency (95%) to visible light in the
range beyond blue light.
Here, CsPb(Cl/Br)
samples with different Cl/Br were obtained by anion exchange [28,29]. Typically, 5 mL octadecene, 0.188 mmol PbX
.5 mL oleylamine and 0.5 mL oleic acid were loaded into a 25 mL four neck flask, degassed at 120 °C for 30 min and heated to 150
C under nitrogen flow, 0.4 mL cesium sterate solution was quickly injected. After 5 s, the reaction mixture was cooled by the ice-
3
nanocrystals were synthesized by the hot injection method as the literature [22] with some adaptions, and the
2
(X = Cl, Br),
0
°
water bath. The resultant nanocrystals were precipitated via centrifugation (10000 rpm, 20 min). And the separated nanocrystals were
redispersed in 10 mL toluene for further use. The concentration of the obtained nanocrystal solution was then denoted as 100%.
Nanocrystal solutions with different concentrations were obtained by adjusting the volume of toluene. Using the anion exchange
reaction between different halide perovskite nanocrystals, perovskite nanocrystals with different Cl/Br ratio could be easily
synthesized. CsPbCl2.75Br0.25, CsPbCl2.5Br0.5 and CsPbCl
2
Br were obtained by mixing different volume of CsPbCl
3
and CsPbBr
3
nanocrystal in the ratio of 11:1, 5:1 and 2:1, respectively. For the fabrication of EC-CsPb(Cl/Br)
3
films, 0.2 g EC were added into 5 mL
perovskite nanocrystals colloid, and the mixture were ultrasonic for 60 min to form a homogenous colloid. The colloid was spin coated
onto an optical glass, and the toluene was evaporated in room temperature.
High resolution transmission electron microscopy (HRTEM) images were obtained by using Tecnai F30 (Philips-FEI, Holland). The
absorption and transmittance spectra were recorded using UV 2450 (Shimadzu, Japan). The fluorescence spectra were recorded using
F-4500 (Hitachi, Japan) under excitation wavelength of 385 nm, and the excitation and emission slits were set to be 2.5 and 5 nm. The
photostability of the sample was evaluated by collecting the transmittance spectra after the irradiation with a UV lamp (365 nm, 100
2
W/m ) for 0, 2, and 6 days.
Fig. 1 shows the HRTEM images of the nanocrystals with different Cl/Br ratio. The nanocrystals are symmetric cubic, uniform
dispersed and the average size is approximately 10 nm. Obviously, the anion exchange reaction between CsPbCl
preserves the pristine crystal structures.
3
and CsPbBr
3
The UV-vis spectra of samples of different Br/Cl ratio are illustrated in Fig. 2a. The absorption edges of the perovskite nanocrystals
show a red shift with the increase of Br/Cl anion, demonstrating the adsorption edges can be well adjusted by the change of the Br/Cl
ratio. The color of their colloid turns slight yellow with the increase proportion of Br (Inset in Fig. 2a, from left to right), which also
indicates the red shift of absorbance edge.
Here, the EC is selected as the host for the following reasons: (1) EC is dissolved in toluene, in which perovskite nanocrystals could
be well dispersed; (2) The hydrophobic property of EC improves the moisture resistance of the light blocking film; (3) EC is a well
commercialized product that could be easily obtained; (4) The EC is free of absorption in the range from 280 nm to 800 nm, which
enable the film retains high transparency in the visible light range (Fig. 2b); (5) The perovskite NCs retain their optical properties
during the fabricating process, as shown by their photoluminescence spectra (Figs. S1 and S2 in Supporting information).
The light shielding properties of the EC-nanocrystals films were characterized from their UV-vis transmittances. The UV-vis
transmittance spectra of EC-CsPbCl2.5Br0.5 film for different concentrations are evidenced in Fig. 3a. Results indicate that with the
increased concentration of nanocrystals, the UV and blue lights in the range of 280-460 nm are gradually blocked, while the
transparency keeps constant in 480-800 nm. When the concentration of CsPbCl2.5Br0.5 is up to 100%, the UV and blue lights in the
range of 280-460 nm can be completely blocked, indicating the excellent UV and blue light shielding performance of CsPbCl2.5Br0.5
To testify the tunable light blocking prosperity, the UV-vis transmittance spectra of EC-CsPb(Cl/Br) films were investigated. As
shown in Fig. 3b, the light blocking range shifts from 400 nm to 500 nm by changing the Cl/Br ratio. It should be noted that in Fig. 3b,
the concentration of each CsPb(Cl/Br) is 190%, 160%, 130%, 100% and 70%, respectively, since the absorbance coefficient is
increased with the increasing Br proportion. The adjusting of Cl/Br ratio did not affect the transparency of the EC-nanocrystals film as
shown in the digital photographs of EC-CsPb(Cl/Br) films in Fig. 3b.
.
3
3
3
The wavelength for the 5% and 90% cutoff transmittance were selected to evaluate the tunable light blocking properties of EC-
nanocrystals film (Fig. 4). The EC-CsPbCl and EC-CsPbCl2.75Br0.25 films show transmittance of 5% at 412 nm and 429 nm, with a
transmittance edge of 17 and 21 nm, respectively. The EC-CsPbCl Br film exhibits a transmittance of 5% at 459 nm and 90% at 478
3
2

nm (the wavelength for the 5% cutoff transmittance 459 nm plus the transmittance edge 19 nm), which makes it excellent for UV and
blue light shielding. The adjusting of Cl/Br ratio of the nanocrystals allows for the control of light blocking range, making the EC-
CsPb(Cl/Br)
3
films suitable for various optical applications, such as light blocking and optical filters. The EC-CsPbBr shows
3
transmittance of 5% at 498 nm, however, with a broad transmittance edge of 88 nm, indicating the reduced performance for the finely
control of blocking range.
Photostability is one of the most important issues in real application of light blocking materials, and the degradation of the lead
halide perovskite is considered as a critical issue in various applications [30-34]. In this point of view, the stability of the film is highly
demanded to be evaluated. The UV-vis transmittance spectra before and after under 6 days UV exposure under ambient environment is
shown in Fig. S2 (Supporting information), and it is clearly show that the stability of the film is quite well, which might be benefit
from to the excellent photostability of the CsPbCl2.5Br0.5 [23] and the protection of EC matrix.
In summary, we report a CsPb(Cl/Br) nanocrystals based UV and blue light blocking material. The perovskite nanocrystals retained
3
their photochemical and physical properties during the fabricating process, and the light blocking range is tunable by changing the
Cl/Br ratio. The materials show high transparency beyond the blue light range (> 95%), which offer the great advantage in various
applications.
Acknowledgment
This research was financially supported by the National Nature Scientific Foundation of China (No. 21675133) and OESACLS201902,
which are gratefully acknowledged.
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Fig. 1. TEM images of the CsPb(Cl/Br)
3 3 2
nanocrystals with different Br/Cl ratio. (a) CsPbCl , (b) CsPbCl2.75Br0.25, (c) CsPbCl2.5Br0.5, (d) CsPbCl Br and (e)
CsPbBr . The CsPb(Cl/Br) is prepared from anion exchange reaction.
3
3

b 1
00
a 0.4
8
6
4
2
0
0
0
0
0
0
0
0
0
.3
.2
.1
CsPbCl3
CsPbCl2.75Br0.25
CsPbCl2.5Br0.5
CsPbCl Br
2
CsPbBr3
.0
3
00
400
500
600
700
800
300 400 500 600 700 800
Wavelength (nm)
Wavelength (nm)
Fig. 2. (a) The UV-vis absorbance spectra of CsPb(Cl/Br)
3 3
dispersed in toluene (the concentration of the CsPb(Cl/Br) is 25%). Inset is the digital picture of the
prepared CsPb(Cl/Br) with different Cl/Br ratio. (b) UV-vis transmittance spectra of EC film. Inset is the digital photo of the EC film.
3

a 100
b 100
8
6
4
2
0
0
0
0
0
80
60
40
20
0
CsPbCl3
5%
CsPbCl2.75Br0.25
CsPbCl2.5Br0.5
2
5
7
1
5%
0%
5%
00%
CsPbCl Br
2
CsPbBr3
3
00 400 500 600 700 800
Wavelength (nm)
300 400 500 600 700 800
Wavelength (nm)
Fig. 3. (a) Concentration-dependent UV-vis transmittance spectra of EC-CsPbCl2.5Br0.5 films. Inset graph is the digital photo of the EC-CsPbCl2.5Br0.5 films with
concentration of 5%, 25%, 50%, 75%, and 100% (from left to right). (b) Br/Cl ratio-dependent UV-vis transmittance spectra of the EC-CsPb(Cl/Br) films. Inset
is the digital photo of the EC-CsPb(Cl/Br) films with different Br/Cl ratio.
3
3

CsPbBr3
498
459
443
429
412
88
CsPbCl Br
19
2
CsPbCl2.5Br0.5
18
21
CsPbCl2.75Br0.25
Transmittance edge
5% cut off
CsPbCl3
3
17
00 350 400
450 500
550 600
Wavelength (nm)
3
Fig. 4. The wavelength for 5% cutoff transmittance and the transmittance edge of the EC film containing different Br/Cl ratio of CsPb(Cl/Br) nanocrystals.