NovelSeriesofQuasi-2DRuddlesden–PopperPerovskitesBasedonShort-ChainedSpacerCationforEnhancedPhotodetection资源-CSDN文库

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Novel Series of Quasi-2D Ruddlesden−Popper Perovskites Based on

Short-Chained Spacer Cation for Enhanced Photodetection

Ruoting Dong,

†

Changyong Lan,

†,∥

Xiuwen Xu,

†

Xiaoguang Liang,

†,⊥

Xiaoying Hu,

∥

Dapan Li,

†,⊥

Ziyao Zhou,

†,⊥

Lei Shu,

†,‡,⊥

SenPo Yip,

†,‡,⊥

Chun Li,

∥

Sai-Wing Tsang,

†

and Johnny C. Ho*

,†,‡,§,⊥

†

Department of Materials Science and Engineering,

‡

State Key Laboratory of Millimeter Waves, and

Centre for Functional

Photonics, City University of Hong Kong, Kowloon 999077, Hong Kong

∥

School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, P.

R. China

⊥

Shenzhen Research Institute, City University of Hong Kong, Shenzhen 518057, P. R. China

Supporting Information

ABSTRACT: Quasi two-dimensional (2D) layered organic−inorganic perovskite materials (e.g., (BA)

(MA)

n−1

3n+1

;BA=

butylamine; MA = methylamine) have recently attracted wide attention because of their superior moisture stability as compared

with three-dimensional counterparts. Inevitably, hydrophobic yet insulating long-chained organic cations improve the stability at

the cost of hindering charge transport, leading to the unsatisﬁed performance of subsequently fabricated devices. Here, we

reported the synthesis of quasi-2D (iBA)

(MA)

n−1

3n+1

perovskites, where the relatively pure-phase (iBA)

PbI

and

(iBA)

ﬁlms can be obtained. Because of the shorter-branched chain of iBA as compared with that of its linear

equivalent (n-butylamine, BA), the resulting (iBA)

(MA)

n−1

3n+1

perovskites exhibit much enhanced photodetection

properties without sacriﬁcing their excellent stability. Through hot-casting, the optimized (iBA)

(MA)

n−1

3n+1

perovskite ﬁlms

with n = 4 give the signiﬁcantly improved crystallinity, demonstrating the high responsivity of 117.09 mA/W, large on−oﬀ ratio

of 4.0 × 10

, and fast response speed (rise and decay time of 16 and 15 ms, respectively). These ﬁgure-of-merits are comparable

or even better than those of state-of-the-art quasi-2D perovskite-based photodetectors reported to date. Our work not only paves

a practical way for future perovskite photodetector fabrication via modulation of their intrinsic material properties but also

provides a direction for further performance enhancement of other perovskite optoelectronics.

KEYWORDS: quasi-2D, Ruddlesden−Popper perovskite, thin ﬁlm, short-chained spacer, hot-cast, photodetection

■

INTRODUCTION

In recent years, three-dimensional (3D) organic−inorganic

halide perovskite materials, such as MAPbI

(MA = CH

have attracted wide attention because of the fast development

of solar cells based on them.

1−4

Particularly, the power

conversion eﬃciency of these 3D hybrid halide perovskites

has been increased from 3.81 to 22.1% in just a few years.

5−8

Owing to the excellent light absorption coeﬃcients, long charge

diﬀusion lengths, high carrier mobility, direct band gap, and low

rates of nonradiative charge recombination,

9, 10

organic−

inorganic halide perovskites also ﬁnd extensive applications in

light-emitting diodes (LEDs),

11−13

photodetectors (PDs),

14,15

nanolasers,

transistors,

etc. However, these perov skite

materials still inevitably suﬀer from the inherent instability

over moisture, heat, and light, which seriously hampers their

practical utilizations.

18,19

At the same time, quasi two-dimensional (quasi-2D) layered

perovskite materials (also known as Ruddlesden−Popper, RP,

phases) have the crystal structure consisting of quasi-2D

perovskite slabs interleaved with cations,

in which they

generally adopt a chemical formula of L

n−1

3n+1

, where L is

a large size or long-chain organic cation, A is a regular cation, B

is a divalent metal cation, and X is a halide.

21−23

The variable n

is an integer, indicating the number of metal halide octahedral

Received: March 1, 2018

Accepted: May 9, 2018

Published: May 9, 2018

Research Article

www.acsami.org

Cite This: ACS Appl. Mater. Interfaces 2018, 10, 19019−19026

ACS Appl. Mater. Interfaces 2018, 10, 19019−19026

layers between the two L cation layers.

24−26

For example, for

(BA)

(MA)

n−1

3n+1

(BA = CH

(CH

)

,MA=

) materials, the (MA)

n−1

3n+1

layer is sandwiched

by two BA layers. These basic layers would then stack along the

c axis via van der Waals interaction, forming the bulk quasi-2D

layered perovskite material. If n becomes inﬁnite, the material

would become MAPbI

, the conventional 3D perovski te

material. Lately, it has been reported that these quasi-2D

layered perovskite materials are more stable as compared with

their 3D counterparts.

27,28

Smith et al. demonstrated that

(PEA)

(MA)

(PEA = C

(CH

)

) can be simply

deposited by spin-coating and subsequent high-temperature

annealing processes as high-quality quasi-2D layered perovskite

ﬁlms with the good moisture stability, where the fabricated

perovskite solar cells exhibit a power conversion eﬃ ciency of

4.73%.

In addition, Cao et al. also prepared a series of

(BA)

(MA)

n−1

3n+1

with n = 1, 2, 3, 4 and found that these

quasi-2D perovskites are surprisingly stable, in which the

correspondingly fabricated solar cells can retain their photo-

voltaic performance even after long-duration exposure in

humidity environments.

Thereafter, the widespread inves-

tigation on exploring the fundamental properties of quasi-2D

perovskites and their exploitations in high-performance

optoelectronic devices have been stimulated. Guo and his

group thoroughly studied the electron-phonon scattering of

atomically thin (BA)

(MA)

n−1

3n+1

layers,

while Kammin-

ga et al. systematically investigated the quantum conﬁnement

phenomena in these low-dimensional lead iodide perovskite

hybrids.

Dou and his team also prepared (BA)

PbBr

ﬂakes

with the atomic thickness and reve aled the ir thickness-

dependent photoluminescence (PL), being similar to the

graphene-like 2D materials.

Notably, Liang et al. fabricated

LEDs based on (PEA)

PbBr

(PEA = C

which yield the eﬃcient room-temperature violet electro-

luminescence at 410 nm with a narrow bandwidth.

All these

ﬁndings evidently indicate their great potentials as the active

materials in state-of-the-art optoelectronics.

Among many quasi-2D layered perovskite materials,

(BA)

(MA)

n−1

3n+1

is one of the most intensively studied

materials because of the ease of its synthesis and unique

properties. Interestingly, the fabricated ﬁ lm of

(BA)

(MA)

n−1

3n+1

is shown w ith the n-dependent

orientation. When n is below 4, the ﬁlm maintains a preferential

orientation of the basal plane (i.e., the sandwiched plane). For n

= 4, the ﬁlm does not display any more the basal plane

orientation. In this case, because the BA layer is insulating,

being detrimental for the carrier transport, the resulting ﬁlm

would yield the poor photoelectric properties.

Taking it into

consideration, Tsai et al. have made use of this character and

optimized to obtain (BA)

(MA)

-based solar cells, which

exhibit the much enhanced photovoltaic eﬃciency of 12.5%.

Inevitably, as the large BA spacer cation possesses the long

linear chain hindering the collection of charge carriers, the

corresponding carrier mobility would get degraded, particularly

in the deep layer of the perovskites, and hence signiﬁcantly

undermine their optoelectronic performances. It is noted that

when the linear chain BA cation is substituted by the branched

chain iBA counterpart, the obtained ﬁlm crystallinity as well as

the air stability would get improved, which can be attributed to

the more eﬀ ective packing of branched alkane chains.

The

solar cells based on hot-casted (iBA)

(MA)

ﬁlms can

then yield a respectable power conversion eﬃciency of

10.63%.

In any case, there is still very limited investigation

on the systematic synthesis and the eﬀect of crystal orientation

on the optoelectronic properties of (iBA)

(MA)

n−1

3n+1

layered perovskites with varied values of n.

In this work, iso-butylamine (iBA), an isomer to linear n-

butylamine (BA), has short-branched chain and is deliberately

chosen as the spacer cation to synthesize a set of novel quasi-

2D RP perovskites. In speciﬁc, we have systematically

investigated the synthesis of (iBA)

(MA)

n−1

3n+1

(n =1,2,

3, and 4) layered perovskite ﬁlms and found that relatively pure

phases can be obtained for n = 1 and 4. Mixed phases are

obtained for n = 2 and 3 with the main phase of (iBA)

PbI

and

(iBA)

MAPb

, respectively. All these ﬁlms exhibit the

excellent stability in air, without any noticeable degradation

even after the exposure in controlled humidity environments

for 60 days. Importantly, PDs made from these layered

perovskite ﬁlms are demonstrated with the impressive photo-

sensing performance. Through a hot-casting method, the 2D

perovskite with n = 4, namely, (iBA)

(MA)

, reveals the

improved crystallinity and the PD performance, which are

comparable with or even better than those of state-of-the-art

quasi-2D perovskite PDs reported to date. All these results not

only provide important guidelines for the future quasi-2D RP

perovskite-based device construction from the viewpoint of

tailoring intrinsic material properties via their synthesis but also

oﬀer a direction for the further performance enhancement of

other quasi-2D perovskite optoelectronic devices.

■

EXPERIMENTAL SECTION

Perovskite Precursor Synthesis. Precursor solutions were

prepared by dissolving PbI

, HI, and CH

Iata

molar ratio of n:2:2:n − 1 in dimethyl formamide (DMF). The total

molar concentration is 2 M in the solutions. The solutions were

then stirred at room temperature overnight.

Device Fabrication. The fabrication of PDs started with the one-

step spin-coating method of perovskite precursor solution in a

nitrogen-ﬁlled glovebox, where the oxygen and moisture concentration

are well-controlled at the ppm level. Speciﬁcally, the glass substrates

were ﬁrst ultrasonically washed by acetone and ethanol and deionized

water for 15 min in succession, followed by a mild oxygen plasma

treatment for 5 min (0.26 Torr, 30 W). After that, 50 μL of precursor

solution was spin-coated on the glass substrate at 3000 rpm for 30 s,

subsequently with a thermal annealing at 100 °C for 15 min for the full

crystallization of samples. The samples for n = 1, 2, 3, and 4 are labeled

as #1, #2, #3, and #4, respectively. The thickness of the samples was

determined by atomic force microscopy (AFM) and is found to be

665, 405, 540, and 419 nm for #1, #2, #3, and #4, respectively. In the

case of employing hot-casting during the fabrication, prior to spin-

coating, the precursor solution and substrate were preheated at 120

°C. Then, the hot-casted sample #4 has a thickness of 529 nm. Finally,

with the assistance of a shadow mask, gold (100 nm) was thermally

evaporated on the ﬁlms as electrodes. The channel length of the

devices is 10 μm.

Film and Device Characterization. Surface morphologies of all

the samples were characterized with scanning electron microscopy

(SEM, Quanta FEG450) and AFM (diMultimode V, Veeco). X-ray

diﬀraction (XRD, D2 PHASER with Cu Kα radiation, Bruker) was

used to evaluate the crystallinity and crystal structure of the products.

UV−vis absorption spectra were recorded using a PerkinElmer model

Lambda 2S UV−vis spectrometer. The PL spectra were acquired by

iHR320 photoluminescence spectroscopy with an excitation wave-

length of 425 nm. Time-resolved photoluminescence (TRPL)

measurement was performed on a time-correlated single-photon

counting spectrometer from Edinburgh Instruments (LifeSpec II). The

electrical performance of the fabricated device was characterized with a

standard electrical probe station and an Agilent 4155C semiconductor

analyzer (Agilent Technologies, California, USA). A 532 nm laser

diode was used as the light source for the photodetection

ACS Applied Materials & Interfaces Research Article

DOI: 10.1021/acsami.8b03517

ACS Appl. Mater. Interfaces 2018, 10, 19019−19026

19020

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