Cost-effective hole transporting material for stable and efficient perovskite solar cells with fill factors up to 82%

Article abstract of DOI:10.1039/c7ta08053k

A new small molecule-based hole selective material (HSM), 4,4′,4′′-(7,7′,7′′-(5,5,10,10,15,15-hexahexyl-10,15-dihydro-5H-diindeno[1,2-a:1′,2′-c]fluorene-2,7,12-triyl)tris(2,3-dihydrothieno[3,4-b][1,4]dioxine-7,5-diyl))tris(N,N-bis(4-methoxyphenyl)aniline) (TRUX-E-T), has been developed by a facile synthesis with reduced cost. The highest occupied molecular orbital energy level and lowest unoccupied molecular orbital energy level of TRUX-E-T are -5.10 and -2.50 eV, respectively, making it a suitable HSM for lead iodide perovskite solar cells. TRUX-E-T can be smoothly deposited onto perovskite layers, enabling efficient perovskite solar cells with thin TRUX-E-T layers (～50 nm), which helps cut the unit cost of the HSL used in PVSCs to approximately one-fortieth (1/40) of 2,2′,7,7′-tetrakis (N,N-di-p-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD). Additionally, TRUX-E-T exhibits hole mobilities as high as 2.47 × 10^-4 cm² V^-1 s^-1, better than spiro-OMeTAD. As a result, our perovskite solar cells using TRUX-E-T have shown high fill factors up to 82%. The champion cell achieved a maximum power conversion efficiency of 18.35% (16.44%) when measured under reverse (forward) voltage scan under AM1.5 G 100 mW cm^-2 illumination. Our un-encapsulated cells exhibited good stability in ambient air, maintaining 96.4% of their initial efficiency of 18.35% after 20 days of storage.

Full text of DOI:10.1039/c7ta08053k

View Article Online
View Journal
Journal of
Materials Chemistry A
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: L. Guan, X. Yin, D.
Zhao, C. Wang, Q. An, J. Yu, N. Shrestha, C. Grice, R. Awni, Y. Yu, Z. Song, J. Zhou, W. Meng, F. Zhang, R.
Ellingson, J. Wang, W. Tang and Y. Yan, J. Mater. Chem. A, 2017, DOI: 10.1039/C7TA08053K.
This is an Accepted Manuscript, which has been through the
Volume
4 Number 1 7 January 2016 Pages 1–330
Royal Society of Chemistry peer review process and has been
accepted for publication.
Journal of
Materials Chemistry A
Accepted Manuscripts are published online shortly after
Materials for energy and sustainability
www.rsc.org/MaterialsA
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 2050-7488
PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS2 nanocages as a lithium ion battery anode material
rsc.li/materials-a

Page 1 of 19
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C7TA08053K
Cost-Effective Hole Transporting Material for Stable and Efficient
Perovskite Solar Cells with Fill Factors up to 82%
Lei Guan,§,a,b Xinxing Yin,§,c Dewei Zhao,§,b Changlei Wang,b Qiaoshi An,d Jiangsheng Yu,c
Niraj Shrestha,b Corey R. Grice,b Rasha A. Awni,b Yue Yu,b Zhaoning Song,b Jie Zhou,c
Weiwei Meng,b Fujun Zhang,d Randy J. Ellingson,b Jianbo Wang,*,a,e Weihua Tang,*,c and
Yanfa Yan*,b
aSchool of Physics and Technology, Center for Electron Microscopy, MOE Key
Laboratory of Artificial Microꢀ and Nanoꢀstructures, and Institute for Advanced Studies,
Wuhan University, Wuhan 430072, China
bDepartment of Physics and Astronomy, Wright Center for Photovoltaics Innovation and
Commercialization, The University of Toledo, Toledo, OH 43606, United States.
cKey Laboratory of Soft Chemistry and Functional Materials, Nanjing University of
Science and Technology, Nanjing 210094, China
dKey Laboratory of Luminescence and Optical Information, Beijing Jiaotong University,
Beijing 100044, China
eScience and Technology of High Strength Structural Materials Laboratory, Central
South University, Changsha 410083, China
§ These authors contributed equally to this work.
*Corresponding authors:
Jianbo Wang (wang@whu.edu.cn),
Weihua Tang (whtang@njust.edu.cn),
Yanfa Yan (yanfa.yan@utoledo.edu).
Page 1 of 18

Journal of Materials Chemistry A
Page 2 of 19
View Article Online
DOI: 10.1039/C7TA08053K
Abstract:
A
new
small
moleculeꢀbased
hole
selective
material
(HSM),
4,4',4''ꢀ(7,7',7''ꢀ(5,5,10,10,15,15ꢀhexahexylꢀ10,15ꢀdihydroꢀ5Hꢀdiindeno[1,2ꢀa:1',2'ꢀc]fluoreneꢀ
2,7,12ꢀtriyl)tris(2,3ꢀdihydrothieno[3,4ꢀb][1,4]dioxineꢀ7,5ꢀdiyl))tris(N,Nꢀbis(4ꢀmethoxyphenyl
)aniline) (TRUXꢀEꢀT), has been developed by a facile synthesis with reduced cost. The
highest occupied molecular orbital energy level and lowest unoccupied molecular
orbital energy level of TRUXꢀEꢀT are ꢀ5.10 and ꢀ2.50 eV, respectively, making it a suitable
HSM for lead iodide perovskite solar cells. TRUXꢀEꢀT can be smoothly deposited onto
perovskite layers, enabling efficient perovskite solar cells with thin TRUXꢀEꢀT layers (~50
nm), which helps cut the unit cost of the HSL used in PVSCs to approximately oneꢀfortieth
(1/40)
of
2,2′,7,7′ꢀTetrakis
(N,Nꢀdiꢀpꢀmethoxyphenylamino)ꢀ9,9′ꢀspirobifluorene
(spiroꢀOMeTAD). Additionally, TRUXꢀEꢀT exhibits hole mobility as high as 2.47×10ꢀ4
cm2/Vs, better than spiroꢀOMeTAD. As a result, our perovskite solar cells using TRUXꢀEꢀT
have shown high fill factors up to 82%. The champion cell achieved a maximum power
conversion efficiency of 18.35% (16.44%) when measured under reverse (forward) voltage
scan under AM1.5 G 100 mW/cm2 illumination. Our unꢀencapsulated cells exhibited good
stability in ambient air, maintaining 96.4% of their initial efficiency of 18.35% after 20 days
storage.
Page 2 of 18

Page 3 of 19
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C7TA08053K
1. Introduction
Perovskite solar cells (PVSCs) have attracted enormous attention in recent years due to
their high optical absorption coefficients and very long carrier lifetimes.1ꢀ6 The power
conversion efficiency (PCE) has increased from 3.8% to over 22% in the past few years.7ꢀ16
PVSCs are typically fabricated by sandwiching a perovskite absorber layer with an electron
selective layer (ESL) and a hole selective layer (HSL). The ESL and HSL separate and extract
photogenerated electrons and holes in the perovskite absorber, respectively. Therefore, the
PCE of a PVSC relies significantly on the optoelectronic properties of ESL and HSL materials,
such as the energy levels of band edges, bandgaps, and carrier mobility. Inappropriate ESLs
and HSLs can adversely affect the openꢀcircuit voltages (Vocs) and fill factors (FFs) of
PVSCs.17, 18 So far, PVSCs with record PCEs typically use TiO2 ESLs and spiroꢀOMeTAD is
2,2′,7,7′ꢀTetrakis (N,Nꢀdiꢀpꢀmethoxyphenylamino)ꢀ9,9′ꢀspirobifluorene (spiroꢀOMeTAD)
HSLs.7, 19 The main drawbacks of using spiroꢀOMeTAD HSLs in PVSCs include: (1) high
cost for synthesizing pure spiroꢀOMeTAD; (2) poor charge transport mobility; (3)
requirements for pꢀtype dopants such as cobalt complexes which may result in chemical
o
degradation;20 (4) low thermal stability and crystallization at temperatures as low as 60 C.
These drawbacks limit the largeꢀscale commercialization of PVSCs using spiroꢀOMeTAD
HSLs. Compared with polymer semiconductors, organic smallꢀmolecule HSLs have some
unique advantages, such as easy modification and purification, lowꢀcost solution processing at
low temperature, wellꢀdefined chemical structures, and molecular weights with negligible
batchꢀtoꢀbatch variation.21ꢀ24 For example, triazatruxene is one of such organic
smallꢀmolecule HSL materials and has been successfully used as HTLs for PVSCs.25, 26
However, the synthesis of triazatruxene involves harsh phosphorus oxychloride regent that
greatly hinders its largeꢀscale application.25, 26
Aiming to obtain an ideal HSL with low cost, high thermal stability and high hole
transport without using Co dopant, we have designed
a
new HSL,
4,4',4''ꢀ(7,7',7''ꢀ(5,5,10,10,15,15ꢀhexahexylꢀ10,15ꢀdihydroꢀ5Hꢀdiindeno[1,2ꢀa:1',2'ꢀc]fluoreneꢀ
2,7,12ꢀtriyl)tris(2,3ꢀdihydrothieno[3,4ꢀb][1,4]dioxineꢀ7,5ꢀdiyl))tris(N,Nꢀbis(4ꢀmethoxyphenyl
)aniline) (TRUXꢀEꢀT), with a planar molecular geometry containing truxene as the core, with
Page 3 of 18

Journal of Materials Chemistry A
Page 4 of 19
View Article Online
DOI: 10.1039/C7TA08053K
3,4ꢀethylenedioxythiophene (EDOT) as a πꢀlinker, and methoxyꢀsubstituted triphenylamine
(TPA) as arms. Unlike the orthogonal spiro core, truxene has a planar and fused molecular
structure, which enables the HSL to show strong πꢀπ stacking through intermolecular
interactions, thereby leading to enhanced hole mobility. The fully conjugated truxene core
also provides great potential for improved thermal and optical stability. Moreover, it offers
good chemical versatility to tune solubility, 3D configuration and optoelectronic properties.27,
28 Compared to triazatruxene, truxene can be synthesized by facile methods and it consists six
hydrophobic hexyl chains which should work better for both preventing the perovskite surface
from the moisture and suppressing crystal growth of HSL to obtain better film.27, 29 As proven
in previous reports, the incorporation of EDOT unit can enhance charge transport and improve
device performance without sacrificing stability.30, 31 TPA has 3D πꢀconjugated molecular
configuration, which can restrict aggregation and promote exciton separation. The
propellerꢀlike structure of TPA is also beneficial for forming uniform and smooth thin films
with stable amorphous morphology and homogeneous features.32 A combination of EDOT
bridge with TPA arms can endow TRUXꢀEꢀT with suitable energy levels and efficient
holeꢀtransporting properties.18, 25, 26, 33ꢀ35
With the aforementioned considerations, we herein report on the synthesis and
characterization of TRUXꢀEꢀT and its application as HSLs in efficient PVSCs. We show that
highꢀquality TRUXꢀEꢀT can be synthesized by a facile route, ensuring a low cost.
Characterizations reveal that the highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LOMO) energy levels of TRUXꢀEꢀT are at ꢀ5.10 and ꢀ2.50
eV, respectively, which are suitable as HSLs for effective charge transfer in PVSCs.
TRUXꢀEꢀT exhibits hole mobility as high as 2.47×10ꢀ4 cm2/Vs as well as efficient charge
transfer at the perovskite/TRUXꢀEꢀT interface. As a result, our PVSCs using TRUXꢀEꢀT have
shown high fill factors (FFs) up to 82%. Additionally, TRUXꢀEꢀT can be smoothly deposited
on perovskite layers, enabling PVSC to use thin TRUXꢀEꢀT layers. Our bestꢀperforming
PVSCs use only ~50 nmꢀthick TRUXꢀEꢀT HSLs, which helps to reduce the unit cost of the
HSL used in PVSCs to approximately oneꢀfortieth (1/40) of that for devices made using
spiroꢀOMeTAD. The champion cell achieved a maximum PCE of 18.35% (16.44%) when
measured under revese (forward) voltage scan under AM1.5 G 100 mW/cm2 illumination.
Page 4 of 18

Page 5 of 19
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C7TA08053K
Our unꢀencapsulated cell exhibited good stability in ambient air, maintaining 96.4% of its
initial efficiency of 18.35% after 20 days storage. It is worth noting that TRUXꢀEꢀT HSLs do
not require Co complex doping, eliminating a significant route for possible degradation.
2. Experimental section
2.1. Material synthesis
TRUX-E-T:
2,7,12ꢀtribromoꢀ5,5,10,10,15,15ꢀhexahexylꢀ10,15ꢀdihydroꢀ5Hꢀdiindeno[1,2ꢀa:1',2'ꢀc]fluorene
(450.0 mg, 0.42 mmol) and
A
solution
of
the
compound
4ꢀmethoxyꢀNꢀ(4ꢀmethoxyphenyl)ꢀNꢀ(4ꢀ(7ꢀ(tributylstannyl)ꢀ2,3ꢀdihydrothieno[3,4ꢀb][1,4]diox
inꢀ5ꢀyl)phenyl)aniline (1.1 g, 1.49 mmol) in dry toluene (40 mL) was degassed twice with N2,
then Pd(PPh3)4 (71.9 mg, 0.062 mmol) was added. After stirring at 110°C for 48 h under N2,
the mixture was cooled to room temperature. After removal of toluene, the crude product was
purified by column chromatography on silica gel (petroleum ether/ethyl acetate, 7:1, v/v) and
recrystallized from methanol to afford TRUXꢀEꢀT (610.0 mg, 67.5%) as a lightꢀyellow solid.
1H NMR (500 MHz, CDCl3, δ): 8.34 (d, J = 8.5 Hz, 3H), 7.85 (d, J = 8.1 Hz, 3H), 7.76 (s,
3H), 7.66 – 7.58 (m, 6H), 7.09 (d, J = 8.4 Hz, 12H), 6.96 (d, J = 8.0 Hz, 6H), 6.89 – 6.79 (m,
12H), 4.50 – 4.34 (m, 12H), 3.81 (s, 18H), 2.93 (m, 6H), 2.18 – 2.06 (m, 6H), 1.03 – 0.78
(m, 36H), 0.68 – 0.50 (m, 30H).13C NMR (125 MHz, CDCl3, δ)156.25, 154.56, 147.68,
141.25, 139.16, 139.06, 138.12, 127.21, 126.88, 125.11, 124.26, 121.18, 119.65, 115.09,
65.14, 65.00, 56.10, 55.90, 37.52, 31.95, 29.98, 24.43 , 22.73, 22.67, 14.42, 14.32.
MALDIꢀTOF MS: m/z=2177.0612 [M+H]+, calcd. for C141H153N3O12S3: 2176.0616.
2.2. Solution preparation
Perovskite precursor: The MA0.7FA0.3PbI3 perovskite precursor was prepared using a
mixture of methylammonium iodide (MAI, Dyesol), formamidium iodide (FAI, Dyesol), lead
iodide (PbI2, Alfa Aesar,99.9985%) and lead thiocyanate (Pb(SCN)2, SigmaꢀAldrich, 99.5%)
in dimethyl sulfoxide (DMSO, SigmaꢀAldrich) and N,Nꢀdimethylformamide (DMF,
SigmaꢀAldrich). The details about the precursor preparation can be found in our previous
papers.34, 36ꢀ38 The precursor solution was stirred on a hotplate at 60oC for several hours. The
Page 5 of 18

Journal of Materials Chemistry A
Page 6 of 19
View Article Online
DOI: 10.1039/C7TA08053K
resulted precursor was purified using a 0.45 ꢁm filter before spinꢀcoating
C60-SAM: C60ꢀselfꢀassembly (SAM) (1ꢀMaterials) was used as purchased. C60ꢀSAM has a
concentration of 4 mg/mL inchlorobenzene (SigmaꢀAldrich, 99.8%).
Spiro-OMeTAD:
2,2’,7,7’ꢀTetrakis(N,N’ꢀdiꢀpꢀmethoxyphenylamine)ꢀ9,9’ꢀspirobifluorene
(spiroꢀOMeTAD) was used to fabricate the reference HSLs and deposited on the perovskite
film at 2000 rpm for 60 s. The spiroꢀOMeTAD was coꢀdoped using Co(II)ꢀ
bisꢀ(trifluoromethanesulfonyl) imide (TFSI) and LiꢀTFSI. The spiroꢀOMeTAD solution was
prepared by dissolving 72.3 mg spiroꢀOMeTAD (Shenzhen Feiming Science and Technology
Co., Ltd.) in 1 mL chlorobenzene (CB) with 28 ꢁL 4ꢀtertꢀbutylpyridine (tBP) (SigmaꢀAldrich),
18 ꢁL LiꢀTFSI (SigmaꢀAldrich) (520 mg/mL in acetonitrile) and 18 ꢁL Co(II)ꢀTFSI salt
(FK102, Dyesol) (300 mg/mL in acetonitrile).
TRUX-E-T: A solution of TRUXꢀEꢀT/chlorobenzene (20mg/ml) with an additive of 15 ꢁl
LiꢀTFSI (170 mg/mL in acetonitrile) and 8ꢁL tBP.
2.3. Device fabrication
The Florineꢀdoped Tin Oxide (FTO) glass substrates were cleaned by ultraꢀsonication in
diluted Microꢀ90 detergent, deionized water, acetone, and 2ꢀpropanol for 15 min, respectively.
SnO2 ETLs were deposited on FTO using a plasmaꢀenhanced atomic layer deposition
(PEALD) method34, 37ꢀ42 and then annealed on a hotplate at 100°C for 1 hour in ambient air
(approximately 25 °C and 55% relative humidity). The substrates were then transferred into a
nitrogen filled glove box. The C60ꢀSAM solution was spinꢀcoated onto the SnO2 layer at 3000
rpm for 1 min. The perovskite layer was deposited by dripping diethyl ether via the
antiꢀsolvent technique. The perovskite film was annealed at 100 oC for 5 min.
SpiroꢀOMeTAD was deposited on the perovskite film at 3000 rpm for 60 s. The TRUXꢀEꢀT
was spinꢀcoated on the perovskite film at 3500 rpm for 45s, leading to an approximately 50
nmꢀthick layer. A layer of 50 nm gold was finally deposited on the top of the HSLs using
thermal evaporation. The active area of the device was 0.08 cm2 as defined by a shadow mask
during the Au evaporation. For holeꢀonly devices, a 30 nm PEDOT:PSS layer was coated on
ITO substrate, followed by the deposition of TRUXꢀEꢀT or spiroꢀOMeTAD layer and then 8
nm MoO3, and 75 nm Ag layers. MoO3 and Ag were thermally evaporated to complete the
Page 6 of 18

Page 7 of 19
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C7TA08053K
device fabrication.
2.4. Film and device characterization
Crossꢀsectional scanning electron microscopy (SEM) image of the completed
devices was taken with Hitachi Sꢀ4800. Tappingꢀmode atomic force microscopy (AFM)
images were taken with a Veeco Nanoscope V instrument. Layer thicknesses were
determined using a Dektak surface profiler and crossꢀsectional SEM images. Samples
were illuminated through the glass side for photoluminescence (PL) measurements. A
532 nm cw laser at 38 mW cmꢀ2 was used as a source of excitation for steadyꢀstate PL
while a 532 nm pulsed laser (pulse width ~5 ps) at ~109 photons pulseꢀ1 cmꢀ2 was used
⋅ ⋅
as a source of excitation for TRPL measurement. PL decay curves were fitted by
iterative reꢀconvolution with the measured system response function. Mean
photogenerated carrier lifetimes for the biꢀexponential fit were calculated by the
weighted average method.38
JꢀV curves were recorded in air under 100 mW/cm2AM1.5G solar irradiation (PV
Measurements Inc.) with a Keithley 2400 Source Meter. The light intensity for JꢀV
measurements was calibrated by a standard Si solar cell and our perovskite solar cells
certified by Newport.16 External quantum efficiency (EQE) spectra were measured on
a QE system (PV Measurements Inc., model IVQE8ꢀC QE system without bias
voltage)using 100 Hz chopped monochromatic light. The steadyꢀstate efficiencies were
obtained by tracking the maximum output power point. The JꢀV curves for light
intensity dependence were taken by neutral density filters between 1 and 100 mW/cm2.
The unꢀencapsulated cells for stability test were stored in ambient air (45% humidity
and room temperature). All characterizations and measurements were performed in the
ambient air.
3. Results and discussion
3.1. TRUX-E-T synthesis and characterization
The synthesis of TRUXꢀEꢀT is displayed in Scheme 1. A oneꢀstep Still coupling of
2,7,12ꢀtribromoꢀ5,5,10,10,15,15ꢀhexahexylꢀ10,15ꢀdihydroꢀ5Hꢀdiindeno[1,2ꢀa:1',2'ꢀc]fluorene
and
Page 7 of 18

Journal of Materials Chemistry A
Page 8 of 19
View Article Online
DOI: 10.1039/C7TA08053K
4ꢀmethoxyꢀ
[1,4]dioxinꢀ5ꢀyl)phenyl)aniline was readily afforded TRUXꢀEꢀT with a yield of 67.5%.
The tribromotuxene was prepared via a threeꢀstep procedure, i.e., cyclization of
Nꢀ(4ꢀmethoxyphenyl)ꢀNꢀ(4ꢀ(7ꢀ(tributylstannyl)ꢀ2,3ꢀdihydrothieno[3,4ꢀb]
3
truxene using 1ꢀindanone, alkylation and bromination. The tin reagent was prepared
according to the literature.43 The synthetic pathways and experimental details are
available in Electronic Supplementary Information (ESI). TRUXꢀEꢀT was acquired
as a lightꢀyellow solid after silicaꢀgel column chromatography and recrystallization
from methanol. During the purification of TRUXꢀEꢀT, no expensive sublimation step
is involved, which is necessary for spiroꢀOMeTAD instead.44 The structure of
1
TRUXꢀEꢀT is confirmed by H and 13C NMR spectra and MALDIꢀTOF mass
spectrometry (Figure S1-S6).
OCH3
H3CO
N
Br
C4H9
C4H9
Sn
C6H13
C6H13
O
O
O
C4H9
S
S
O
C6H13
Br
Pd(PPh3)4
+
C6H13
toluene, 110o
C
C6H13
C6H13
C6H13
C6H13
C6H13
C6H13
N
O
Br
O
H3CO
OCH3
OCH3
C6H13
S
S
C6H13
O
N
H3CO
O
N
TRUX-E-T
OCH3
OCH3
Scheme 1. Synthetic route of TRUXꢀEꢀT
Figure S7 shows thermogravimetric analysis (TGA) of TRUXꢀEꢀT, exhibiting
decomposition temperature (5% weight loss) at 421oC in nitrogen atmosphere. This
result indicates the excellent inherent thermal stability of TRUXꢀEꢀT, which would
benefit the longꢀterm stability of PVSCs with TRUXꢀEꢀT HSLs. Differential scanning
calorimetry (DSC) shown in Figure S8 exhibits a clear glass transition at around
202oC, indicating the amorphous nature of asꢀsynthesized TRUXꢀEꢀT.
Page 8 of 18

Page 9 of 19
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C7TA08053K
Figure 1. (a) Absorption and PL spectra of a TRUXꢀEꢀT film. (b) Cyclic voltammetry (CV) of
TRUXꢀEꢀT. The inset shows CV plot for ferrocene/ferrocenium as reference. DFTꢀcalculated
electronic structure of TRUXꢀEꢀT, showing the electronic energy levels of (c) HOMO and (d) LUMO.
(e) Calculation of the hole reorganization energy for TRUXꢀEꢀT.
The normalized absorption and photoluminescence (PL) spectra of a TRUXꢀEꢀT film are
shown in Figure 1a. TRUXꢀEꢀT shows absorption of photons with an edge of 477 nm and a
maximum peak located at 415 nm. The shoulder in UV region can be attributed to πꢀπ*
transition.26 The optical bandgap (Egopt) of TRUXꢀEꢀT is estimated at 2.60 eV. PL spectrum
shows that TRUXꢀEꢀT has a main emission wavelength centred at 502 nm.
To check energy levels of TRUXꢀEꢀT, electrochemical cyclic voltammetry (CV)
was employed to evaluate its electrochemical properties. Ferrocene/ferrocenium was
used as a reference with a potential of 0.55V vs. Ag/AgCl electrode. As shown in
Figure 1b, a clear oxidation peak was observed. From the onset potential for oxidation
(
Eox), the HOMO energy level was determined to be ꢀ5.10 eV for TRUXꢀEꢀT, which is
favourable for hole transfer. The corresponding LUMO energy level was estimated to
opt
be ꢀ2.50 eV according to the measured Eg
.
Page 9 of 18

Journal of Materials Chemistry A
Page 10 of 19
View Article Online
DOI: 10.1039/C7TA08053K
The electronic structure and geometry of TRUXꢀEꢀT were also investigated with
density functional theory (DFT) calculation using Gaussian program at the
B3LYP/6ꢀ31G (d,p) level, as shown in Figure 1c and d. The dihedral angles between
three arms and central truxene core are17o, 21o, and 22o, respectively. The relatively
planar molecular configuration can facilitate intermolecular interaction, and thus
enhance charge transport. As shown in Figure 1e, the calculated hole reorganization
energies (λhole) of TRUXꢀEꢀT (87meV) is much smaller than that of spiroꢀOMeTAD
(148 meV), indicating a better holeꢀtransporting property. We compared the hole
mobility of TRUXꢀEꢀT and spiroꢀOMeTAD by making holeꢀonly devices with a
structure
of
ITO/poly(3,4ꢀethylenedioxythiophene):polystyrene
sulfonate
(PEDOT:PSS)/TRUXꢀEꢀT or spiroꢀOMeTAD/MoO3/Ag. The calculation was done by
space chargeꢀlimited current (SCLC) model. The hole mobilities are estimated to be
1.41×10ꢀ4 cm2·Vꢀ1·sꢀ1 and 2.47×10ꢀ4 cm2·Vꢀ1·sꢀ1 for spiroꢀOMeTAD and TRUXꢀEꢀT,
respectively, as shown in Figure S9 (Electronic Supplementary Information (ESI))
.
A higher hole mobility indicates a better hole transport, benefiting the improvement in
charge transport balance within PVSCs. Our calculation and experimental
characterization thus reveal that TRUXꢀEꢀT is suitable as a HSL material for PVSC
fabrication.
3.2. PVSC fabrication and characterization
Figure 2. (a) Crossꢀsectional SEM image of our regular PVSC with TRUXꢀEꢀT HSL. (b) Energy band
diagram of our regular PVSC with TRUXꢀEꢀT as HSL.
Page 10 of 18

Page 11 of 19
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C7TA08053K
Figure 2a shows a crossꢀsectional SEM image of our PVSC using TRUXꢀEꢀT as HSL. The
perovskite absorber is MA0.7FA0.3PbI3 and the PVSC has the regular nꢀiꢀp configuration of
FTO/SnO2/C60ꢀSAM/peroskite/TRUXꢀEꢀT/Au. The SnO2 layer was prepared by
plasmaꢀenhanced atomicꢀlayer deposition (PEALD) and has a thickness of about 20 nm.34, 37,
38, 40, 42The perovskite layer was grown by a oneꢀstep deposition method and has a thickenss of
about 450 nm. We find that TRUXꢀEꢀTcan be smoothly deposited onto the perovskite
absorber layer by solution processing, as evidenced by the AFM images shown in Figure S10.
The root mean square (RMS) roughness of perovskite layer is 10.9 nm, which is reduced to
2.9 nm after the deposition of 50 nm TRUXꢀEꢀT. Figure 2b shows the energy level diagram
of our device using TRUXꢀEꢀT HSL, presenting selective transfer of photogenerated electrons
and holes, i.e., electrons are reflected by TRUXꢀEꢀT and transfer through SnO2 and holes are
reflected by SnO2 and transfer through TRUXꢀEꢀT, which is suitable for PVSCs.
Figure 3. (a) PL spectra and (b) TRPL decays of perovskite film and perovskite/TRUXꢀEꢀT.
To evaluate the effectiveness of hole transfer at the perovskite/TRUXꢀEꢀT interface, we
performed steadyꢀstate photoluminescence (PL) and timeꢀresolved PL (TRPL) measurements
on perovskite films deposited on bare glass substrates and coated with poly(methyl
methacrylate) (PMMA) for protection and TRUXꢀEꢀT. As shown in Figure 3a, the PL
emission of the perovskite film with TRUXꢀEꢀT coated shows a significant quenching as
compared to that of the perovskite film with PMMA coated, indicating an effective charge
transfer at the perovskite/TRUXꢀEꢀT interface. The results are consistent with the TRPL
decays measured from these samples (Figure 3b). The deposition of TRUXꢀEꢀT layer on
perovskite shortens the mean carrier lifetime for perovskite from 650 ns to 23 ns, confirming
Page 11 of 18

Journal of Materials Chemistry A
Page 12 of 19
View Article Online
DOI: 10.1039/C7TA08053K
a fast charge transfer at the perovskite/TRUXꢀEꢀT interface.
Figure 4. (a) JꢀV curves of our bestꢀperforming PVSC with TRUXꢀEꢀT HSL measured under AM
1.5G illumination at reverse and forward voltage scans. (b) EQE spectrum and integrated Jsc of the
bestꢀperforming PVSC based on TRUXꢀEꢀT HSL. (c) Maximum power point tracking of PCE and (d)
Photovoltaic parameters versus time of PVSC with TRUXꢀEꢀT HSL.
Figure 4a shows the current densityꢀvoltage (JꢀV) curves of the bestꢀperforming PVSC
using a 50 nm TRUXꢀEꢀT HSL measured under reverse and forward voltage scans.Our
champion cell achieves a PCE of 18.36 (16.44)% with a Voc of 1.08 (1.04) V, a Jsc of 20.8
(20.8) mA/cm2, and a FF of 81.8 (76.2)% when measured under reverse (forward) voltage
scan. This performance is slightly lower than that of the PVSC with spiroꢀOMeTAD HSLs
(PCE of 19.13 (18.12)% with a Voc of 1.10 (1.09) V, a Jsc of 21.9 (21.9) mA/cm2, and a FF of
78.7 (76.4)% under reverse (forward) voltage scan), as shown in Figure S11. Since the JꢀV
hysteresis has been found in both PVSCs with TRUXꢀEꢀT and spiroꢀOMeTAD HSLs, it might
be attributed to the ESL/perovskite interface37, 40 or perovskite film itself such as ion
migration,45 and/or trap states.46 The EQE spectrum of this cell is shown in Figure 4b. The
integrated Jsc of over a 100 mW/cm2 AM1.5G solar spectrumis 20.92 mA/cm2, which is in
good agreement with the Jsc obtained from the JꢀV curves. The stabilized PCE measured by
Page 12 of 18

Page 13 of 19
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C7TA08053K
the tracking maximum power point is 16.42% (Figure 4c). As mentioned above, TRUXꢀEꢀT
has a good thermal stability, which can help to improve the stability of PVSCs. Therefore, we
measured the dependence of each photovoltaic parameter of unꢀencapsulated PVSCs with
TRUXꢀEꢀT HSLs stored in dark and glove box on the storage time. As shown in Figure 4d,
the cell exhibited a good stability for 20 days, maintaining 96.4% of its initial efficiency of
18.35% when measued under reserse voltage scan and in ambient. The main degradation
originates from FFs dropping from 81.8% to 79.2%, which is likely attributed to the contact
damage of our measured cell with isolated pixel. In other words, the results suggest an
encouragingalternative HSL for stable PVSCs.
Figure 5. Histograms of (a) PCEs, (b) FFs, (c) Vocs, and (d) Jscs measured for 25 cells with
TRUXꢀEꢀTꢀbased PVSCs.
To evaluate the performance reproducibility of PVSCs using the TRUXꢀEꢀT HSLs, we
fabricated and measured 25 PVSCs. The histograms of the PCE, Voc, Jsc, and FF measured
under reverse voltage scan are shown in Figure 5a, b, c, and d, respectively. The average
PCE, Voc, Jsc, and FF for these 25 cells are 17.74±0.62%, 1.08±0.03V, 20.88±0.65 mA/cm2,
Page 13 of 18

Journal of Materials Chemistry A
Page 14 of 19
View Article Online
DOI: 10.1039/C7TA08053K
and 80.7±1.2%, respectively, revealing a good reproducibility.
Figure 6. (a) JꢀV curves of a PVSC with TRUXꢀEꢀT HSLs under different light intensities ranging
from 1 to 100 mW/cm2. Light intensity dependence: (b) Jsc versus light intensity; (c) Voc versus light
intensity; (d) FF versus light intensity.
To understand the charge extraction and recombination mechanism in the PVSCs with
TRUXꢀEꢀT HSLs, the JꢀV characteristics were measured under light intensities varying from
1 to 100 mW/cm2, as shown in Figure 6a. Figure 6b shows the power law relationship
between Jsc and light intensity. It is known that a carrier imbalance or an interfacial barrier
could lead to a space charge limited solar cell with α ~ 0.75.47ꢀ49 An α value close to 1 means
a solar cell with no space charge effect.47ꢀ49 The PVSC with TRUXꢀEꢀT HSL does not appear
to be space charge limited since the α is 0.99, indicating an efficient charge transfer in this
solar cell. The natural logarithmic relationship between light intensity and Voc has a slope of
1.56kBT/q, as shown in Figure 6c, implying that Shockley Reed Hall recombination is
dominant in solar cells,50ꢀ52 which is also consistent with the fact that the FF decreases when
the light intensity increases from 1 to 100 mW/cm2 (Figure 6d). Therefore, the high FF
Page 14 of 18

Page 15 of 19
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C7TA08053K
originates from the efficient charge transfer at the perovskite/HSL interface due to the
appropriate HOMO level and high hole mobility of HSLs.
The estimated lab synthesis and purification cost of TRUXꢀEꢀT is about $38.9/g (see cost
calculation for TRUXꢀEꢀT in Electronic Supplementary Information (ESI)), which is
one thirteenth of that of spiroꢀOMeTAD (about $500/g).53 Furthermore, the typical thickness
of spiroꢀOMeTAD for efficient PVSCs is around 150 nm, while the thickness of TRUXꢀEꢀT
HSLs used in our PVSCs is only about 50 nm. Therefore, the unit cost of TRUXꢀEꢀT used in
PVSCs is roughly one 40th of that of spiroꢀOMeTAD.53 Therefore, our TRUXꢀEꢀT HSL offers
an attractive potential to commercialization of the emerging PVSC technology.
4. Conclusions
We have synthesized and characterized TRUXꢀEꢀT, a new small moleculeꢀbased HSL
material using a facile route. Characterizations reveal that TRUXꢀEꢀT is suitable as HSL for
PVSCs. We found that TRUXꢀEꢀT can be smoothly deposited on perovskite layers, enabling
PVSC to use thin TRUXꢀEꢀT layers. Our bestꢀperforming PVSCs use only ~50nm thick
TRUXꢀEꢀTHSLs, which facilitates the reduction in device cost. The estimated unit cost of
TRUXꢀEꢀT used in PVSCs is roughly one 40th of that of spiroꢀOMeTAD. Finally, TRUXꢀEꢀT
exhibits hole mobility as high as 2.47×10ꢀ4 cm2/Vs, which is responsible for the high FFs of
up to 82% obtained in our PVSCs using thin TRUXꢀEꢀTHSLs.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (51671148,
51271134, J1210061, 11674251, 51501132, 51601132), the Hubei Provincial Natural Science
Foundation of China (2016CFB446, 2016CFB155), the Fundamental Research Funds for the
Central Universities, and the CERSꢀ1ꢀ26 (CERSꢀChina Equipment and Education Resources
System), and the China Postdoctoral Science Foundation (2014T70734), and the Open
Research Fund of Science and Technology on High Strength Structural Materials Laboratory
(Central South University) and the Suzhou Science and Technology project (No.
SYG201619). The design of TRUXꢀEꢀT was completed by the W. Tang’s group at Nanjing
Page 15 of 18

Journal of Materials Chemistry A
Page 16 of 19
View Article Online
DOI: 10.1039/C7TA08053K
University of Science and Technology under the financial support from the National Natural
Science Foundation of China (Grant No. 51573077), the Jiangsu Province Natural Science
Foundation for Distinguished Young Scholars (BK20130032), the Program for New Century
Excellent Talents in University (NCETꢀ12ꢀ0633), and the Priority Academic Program
Development of Jiangsu Higher Education Institutions. This work was also financially
supported by the U.S. Department of Energy (DOE) SunShot Initiative under the Next
Generation Photovoltaics 3 program (DEꢀFOAꢀ0000990), National Science Foundation under
contract no. CHE−1230246 and DMR−1534686, and the Ohio Research Scholar Program.
Ellingson’s group at the University of Toledo received financial support from the National
Science Foundation under contract no. CHE−1230246, and from University of Toledo startup
funds.
References
1.
Q. Dong, Y. Fang, Y. Shao, P. Mulligan, J. Qiu, L. Cao and J. Huang, Science, 2015, 347,
967ꢀ970.
2.
3.
4.
5.
D. B. Mitzi, S. Wang, C. A. Feild, C. A. Chess and A. M. Guloy, Science, 1995, 267, 1473ꢀ1476.
B. Saparov and D. B. Mitzi, Chem. Rev., 2016, 116, 4558ꢀ4596.
W.ꢀJ. Yin, T. Shi and Y. Yan, Adv. Mater., 2014, 26, 4653ꢀ4658.
S. D. Stranks, G. E. Eperon, G. Grancini, C. Menelaou, M. J. P. Alcocer, T. Leijtens, L. M. Herz,
A. Petrozza and H. J. Snaith, Science, 2013, 342, 341ꢀ344.
6.
7.
G. Xing, N. Mathews, S. Sun, S. S. Lim, Y. M. Lam, M. Grätzel, S. Mhaisalkar and T. C. Sum,
Science, 2013, 342, 344ꢀ347.
W. S. Yang, B.ꢀW. Park, E. H. Jung, N. J. Jeon, Y. C. Kim, D. U. Lee, S. S. Shin, J. Seo, E. K.
Kim, J. H. Noh and S. I. Seok, Science, 2017, 356, 1376ꢀ1379.
M. Liu, M. B. Johnston and H. J. Snaith, Nature, 2013, 501, 395ꢀ398.
H. Zhou, Q. Chen, G. Li, S. Luo, T.ꢀb. Song, H.ꢀS. Duan, Z. Hong, J. You, Y. Liu and Y. Yang,
Science, 2014, 345, 542ꢀ546.
8.
9.
10. A. Kojima, K. Teshima, Y. Shirai and T. Miyasaka, J. Am. Chem. Soc., 2009, 131, 6050ꢀ6051.
11. H.ꢀS. Kim, C.ꢀR. Lee, J.ꢀH. Im, K.ꢀB. Lee, T. Moehl, A. Marchioro, S.ꢀJ. Moon, R.
HumphryꢀBaker, J.ꢀH. Yum, J. E. Moser, M. Gratzel and N.ꢀG. Park, Sci. Rep., 2012, 2, 591.
12. N. Ahn, D.ꢀY. Son, I.ꢀH. Jang, S. M. Kang, M. Choi and N.ꢀG. Park, J. Am. Chem. Soc., 2015,
137, 8696ꢀ8699.
13. W. Ke, G. Fang, Q. Liu, L. Xiong, P. Qin, H. Tao, J. Wang, H. Lei, B. Li, J. Wan, G. Yang and Y.
Yan, J. Am. Chem. Soc., 2015, 137, 6730ꢀ6733.
14. D. Bi, C. Yi, J. Luo, J.ꢀD. Décoppet, F. Zhang, Shaik M. Zakeeruddin, X. Li, A. Hagfeldt and M.
Grätzel, Nat. Energy, 2016, 1, 16142.
15. M. Yang, Z. Li, M. O. Reese, O. G. Reid, D. H. Kim, S. Siol, T. R. Klein, Y. Yan, J. J. Berry, M.
F. A. M. van Hest and K. Zhu, Nat. Energy, 2017, 2, 17038.
Page 16 of 18

Page 17 of 19
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C7TA08053K
16. D. Zhao, Y. Yu, C. Wang, W. Liao, N. Shrestha, C. R. Grice, A. J. Cimaroli, L. Guan, R. J.
Ellingson, K. Zhu, X. Zhao, R.ꢀG. Xiong and Y. Yan, Nat. Energy, 2017, 2, 17018.
17. Y. Shao, Y. Yuan and J. Huang, Nat. Energy, 2016, 1, 15001.
18. D. Zhao, M. Sexton, H.ꢀY. Park, G. Baure, J. C. Nino and F. So, Adv. Energy Mater., 2015, 5,
1401855.
19. A. Krishna and A. C. Grimsdale, J. Mater. Chem. A, 2017, 5, 16446ꢀ16466.
20. J. Burschka, A. Dualeh, F. Kessler, E. Baranoff, N.ꢀL. CeveyꢀHa, C. Yi, M. K. Nazeeruddin and
M. Grätzel, J. Am. Chem. Soc., 2011, 133, 18042ꢀ18045.
21. L. Calió, S. Kazim, M. Grätzel and S. Ahmad, Angew. Chem. Int. Ed., 2016, 55, 14522ꢀ14545.
22. J.ꢀP. CorreaꢀBaena, A. Abate, M. Saliba, W. Tress, T. Jesper Jacobsson, M. Gratzel and A.
Hagfeldt, Energy Environ. Sci., 2017, 10, 710ꢀ727.
23. W. Yan, S. Ye, Y. Li, W. Sun, H. Rao, Z. Liu, Z. Bian and C. Huang, Adv. Energy Mater., 2016,
DOI: 10.1002/aenm.201600474.
24. X. Yin, Q. An, J. Yu, F. Guo, Y. Geng, L. Bian, Z. Xu, B. Zhou, L. Xie, F. Zhang and W. Tang,
2016, 6, 25355.
25. K. Rakstys, A. Abate, M. I. Dar, P. Gao, V. Jankauskas, G. Jacopin, E. Kamarauskas, S. Kazim,
S. Ahmad, M. Grätzel and M. K. Nazeeruddin, J. Am. Chem. Soc., 2015, 137, 16172ꢀ16178.
26. K. Rakstys, S. Paek, P. Gao, P. Gratia, T. Marszalek, G. Grancini, K. T. Cho, K. Genevicius, V.
Jankauskas, W. Pisula and M. K. Nazeeruddin, J. Mater. Chem. A, 2017, 5, 7811ꢀ7815.
27. C. Huang, W. Fu, C.ꢀZ. Li, Z. Zhang, W. Qiu, M. Shi, P. Heremans, A. K. Y. Jen and H. Chen, J.
Am. Chem. Soc., 2016, 138, 2528ꢀ2531.
28. J.ꢀL. Wang, Z.ꢀM. Tang, Q. Xiao, Y. Ma and J. Pei, Org. Lett., 2009, 11, 863ꢀ866.
29. P.ꢀY. Su, L.ꢀB. Huang, J.ꢀM. Liu, Y.ꢀF. Chen, L.ꢀM. Xiao, D.ꢀB. Kuang, M. Mayor and C.ꢀY. Su,
J. Mater. Chem. A, 2017, 5, 1913ꢀ1918.
30. P. Ganesan, K. Fu, P. Gao, I. Raabe, K. Schenk, R. Scopelliti, J. Luo, L. H. Wong, M. Gratzel
and M. K. Nazeeruddin, Energy Environ. Sci., 2015, 8, 1986ꢀ1991.
31. H. Li, K. Fu, A. Hagfeldt, M. Grätzel, S. G. Mhaisalkar and A. C. Grimsdale, Angew. Chem. Int.
Ed., 2014, 53, 4085ꢀ4088.
32. J. Wang, K. Liu, L. Ma and X. Zhan, Chem. Rev., 2016, 116, 14675ꢀ14725.
33. H. Chen, W. Fu, C. Huang, Z. Zhang, S. Li, F. Ding, M. Shi, C.ꢀZ. Li, A. K. Y. Jen and H. Chen,
Adv. Energy Mater., 2017, DOI: 10.1002/aenm.201700012, 1700012.
34. Y. Yu, C. Wang, C. R. Grice, N. Shrestha, J. Chen, D. Zhao, W. Liao, A. J. Cimaroli, P. J. Roland,
R. J. Ellingson and Y. Yan, ChemSusChem, 2016, 9, 3288ꢀ3297.
35. M. L. Petrus, T. Bein, T. J. Dingemans and P. Docampo, J. Mater. Chem. A, 2015, 3,
12159ꢀ12162.
36. W. Ke, C. Xiao, C. Wang, B. Saparov, H.ꢀS. Duan, D. Zhao, Z. Xiao, P. Schulz, S. P. Harvey, W.
Liao, W. Meng, Y. Yu, A. J. Cimaroli, C.ꢀS. Jiang, K. Zhu, M. AlꢀJassim, G. Fang, D. B. Mitzi
and Y. Yan, Adv. Mater., 2016, 28, 5214ꢀ5221.
37. C. Wang, C. Xiao, Y. Yu, D. Zhao, R. A. Awni, C. R. Grice, K. Ghimire, D. Constantinou, W.
Liao, A. J. Cimaroli, P. Liu, J. Chen, N. J. Podraza, C.ꢀS. Jiang, M. M. AlꢀJassim, X. Zhao and Y.
Yan,
Adv.
Energy
Mater.
,
2017,
DOI:
10.1002/aenm.201700414,
DOI:
10.1002/aenm.201700414.
38. C. Wang, D. Zhao, C. R. Grice, W. Liao, Y. Yu, A. Cimaroli, N. Shrestha, P. J. Roland, J. Chen,
Z. Yu, P. Liu, N. Cheng, R. J. Ellingson, X. Zhao and Y. Yan, J. Mater. Chem. A, 2016, 4,
Page 17 of 18

Journal of Materials Chemistry A
Page 18 of 19
View Article Online
DOI: 10.1039/C7TA08053K
12080ꢀ12087.
39. C. Wang, L. Guan, D. Zhao, Y. Yu, C. R. Grice, Z. Song, R. A. Awni, J. Chen, J. Wang, X. Zhao
and Y. Yan, ACS Energy Lett., 2017, DOI: 10.1021/acsenergylett.7b00644, 2118ꢀ2124.
40. C. Wang, D. Zhao, Y. Yu, N. Shrestha, C. R. Grice, W. Liao, A. J. Cimaroli, J. Chen, R. J.
Ellingson, X. Zhao and Y. Yan, Nano Energy, 2017, 35, 223ꢀ232.
41. X. Yin, L. Guan, J. Yu, D. Zhao, C. Wang, N. Shrestha, Y. Han, Q. An, J. Zhou, B. Zhou, Y. Yu,
C. R. Grice, R. A. Awni, F. Zhang, J. Wang, R. J. Ellingson, Y. Yan and W. Tang, Nano Energy
,
2017, 40, 163ꢀ169.
42. Y. Yu, C. Wang, C. R. Grice, N. Shrestha, D. Zhao, W. Liao, L. Guan, R. A. Awni, W. Meng, A.
J. Cimaroli, K. Zhu, R. J. Ellingson and Y. Yan, ACS Energy Lett., 2017, DOI:
10.1021/acsenergylett.7b00278, 1177ꢀ1182.
43. Q. Feng, X. Jia, G. Zhou and Z.ꢀS. Wang, Chem. Commun., 2013, 49, 7445ꢀ7447.
44. W. Liao, D. Zhao, Y. Yu, N. Shrestha, K. Ghimire, C. R. Grice, C. Wang, Y. Xiao, A. J. Cimaroli,
R. J. Ellingson, N. J. Podraza, K. Zhu, R.ꢀG. Xiong and Y. Yan, J. Am. Chem. Soc., 2016, 138,
12360ꢀ12363.
45. B. Chen, M. Yang, X. Zheng, C. Wu, W. Li, Y. Yan, J. Bisquert, G. GarciaꢀBelmonte, K. Zhu
and S. Priya, The Journal of Physical Chemistry Letters
,
2015, DOI:
10.1021/acs.jpclett.5b02229, 4693ꢀ4700.
46. Y. Shao, Z. Xiao, C. Bi, Y. Yuan and J. Huang, Nat. Commun., 2014, 5, 5784.
47. D. Bi, L. Yang, G. Boschloo, A. Hagfeldt and E. M. J. Johansson, J. Phys. Chem. Lett., 2013, 4,
1532ꢀ1536.
48. L. J. A. Koster, V. D. Mihailetchi, H. Xie and P. W. M. Blom, Appl. Phys. Lett., 2005, 87,
203502.
49. V. D. Mihailetchi, J. Wildeman and P. W. M. Blom, Phys. Rev. Lett., 2005, 94, 126602.
50. S. R. Cowan, W. L. Leong, N. Banerji, G. Dennler and A. J. Heeger, Adv. Funct. Mater., 2011,
21, 3083ꢀ3092.
51. R. N. Hall, Phys. Rev., 1952, 87, 387ꢀ387.
52. W. Shockley and W. T. Read, Phys. Rev., 1952, 87, 835ꢀ842.
53. M. Saliba, S. Orlandi, T. Matsui, S. Aghazada, M. Cavazzini, J.ꢀP. CorreaꢀBaena, P. Gao, R.
Scopelliti, E. Mosconi, K.ꢀH. Dahmen, F. De Angelis, A. Abate, A. Hagfeldt, G. Pozzi, M.
Graetzel and M. K. Nazeeruddin, Nat. Energy, 2016, 1, 15017.
Page 18 of 18

Page 19 of 19
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C7TA08053K
Table of contents entry
Au
TRUX-E-T
MA0.7FA0.3PbI3
SnO2/C60-SAM
FTO
A cost-effective truxene-based hole selective material has been synthesized by facile
approach, leading to efficient perovskite solar cells with 82% FFs.
Page 1 of 1