Phenanthrenone-based hole transport material for efficient dopant-free perovskite solar cells

Article abstract of DOI:10.1016/j.orgel.2018.11.015

Spiro-OMeTAD is the most popular hole transport material (HTM) for perovskite solar cells. The insertion of one carbonyl group into the spirobifluorene framework in spiro-OMeTAD gave a novel phenanthrenone-based hole transport material (spiro-PT-OMeTAD). It is found that the introduction of one carbonyl group into spiro-PT-OMeTAD led to a big difference in the absorption behaviors, frontier molecular orbital energy levels and hole mobilities. The steady-state photoluminescence characterization and the space-charge-limited-current measurement indicate that this phenanthrenone-based material plays an important role in hole collection and transportation in perovskite solar cells. As a result, the dopant-free perovskite solar cells based on spiro-PT-OMeTAD showed highly improved performance by exhibiting a short-circuit current density of 22.36 mA/cm², an open-circuit voltage of 0.99 V, and a fill factor of 0.62% under 1 sun illumination, which gave an overall power conversion efficiency (PCE) of 13.83%, compared to 10.5% for the spiro-OMeTAD based devices.

Full text of DOI:10.1016/j.orgel.2018.11.015

Accepted Manuscript
Phenanthrenone-based hole transport material for efficient dopant-free perovskite
solar cells
Kaiyi Zou, Peng Gao, Xufeng Ling, Bo Song, Lei Ding, Baoquan Sun, Jian Fan
PII:
S1566-1199(18)30585-8
DOI:
https://doi.org/10.1016/j.orgel.2018.11.015
ORGELE 4978
Reference:
To appear in: Organic Electronics
Received Date: 18 July 2018
Revised Date: 8 November 2018
Accepted Date: 12 November 2018
Please cite this article as: K. Zou, P. Gao, X. Ling, B. Song, L. Ding, B. Sun, J. Fan, Phenanthrenone-
based hole transport material for efficient dopant-free perovskite solar cells, Organic Electronics (2018),
doi: https://doi.org/10.1016/j.orgel.2018.11.015.
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ACCEPTED MANUSCRIPT
Phenanthrenone-based hole transport material for efficient
dopant-free perovskite solar cells
Kaiyi Zou,†a Peng Gao,†a Xufeng Ling,a Bo Song,*b Lei Ding,c Baoquan Sun,*a Jian
Fan*a
aJiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute
of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou,
Jiangsu 215123, China
bLaboratory of Advanced Optoelectronic Materials, College of Chemistry, Chemical
Engineering and Materials Science, Soochow University, Suzhou 215123, China
cCollege of Electrical and Information Engineering, Shaanxi University of Science
and Technology, Xi’an, Shaanxi 710021, China
E-mail: songbo@suda.edu.cn; bqsun@suda.edu.cn; jianfan@suda.edu.cn
† The two authors contribute equally to this paper.
Abstract
Spiro-OMeTAD is the most popular hole transport material (HTM) for perovskite
solar cells. The insertion of one carbonyl group into the spirobifluorene framework in
spiro-OMeTAD gave a novel phenanthrenone-based hole transport material
(spiro-PT-OMeTAD). It is found that the introduction of one carbonyl group into
spiro-PT-OMeTAD led to a big difference in the absorption behaviors, frontier
molecular orbital energy levels and hole mobilities. The steady-state
photoluminescence
characterization
and
the
space-charge-limited-current
measurement indicate that this phenanthrenone-based material plays an important role
in hole collection and transportation in perovskite solar cells. As a result, the
dopant-free perovskite solar cells based on spiro-PT-OMeTAD showed highly
improved performance by exhibiting a short-circuit current density of 22.36 mA/cm2,
an open-circuit voltage of 0.99 V, and a fill factor of 0.62% under 1 sun illumination,
which gave an overall power conversion efficiency (PCE) of 13.83%, compared to
10.5% for the spiro-OMeTAD based devices.

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1. Introduction
Solar energy is a clean, sustainable and renewable energy sources with less negative
impacts on the environment. Although currently the silicon solar cell is the
mainstream commercial solar cell, new photovoltaic technologies including
organometal halid perovskites [1-9] have been developed to achieve low-cost and
high efficiency solar cells. Since Miyasaka et al. reported the application of
CH3NH3PbX3 (X = Br, I) perovskite as a sensitizer in dye-sensitized solar cells with
the efficiency of 3.8% in 2009 [10], a rapid progress in the development of perovskite
solar cells (pero-SC) has led to a PCE booming over 22% [11-12] via interfacial
engineering [13-21] and composition modulation [22-27]. So pero-SC showed the
great potential for efficient solar energy conversion due to its long exciton diffusion
length and exciton lifetime [28-29], high absorption coefficient in the visible range
and low loss in charge recombination [30-31]. So far it has attracted extensive
research interest.
Hole transport materials (HTM) play an important role in charge carrier collection and
transportation, which was produced on the perovskite photoactive layer. In pero-SC,
organic molecular compounds [32-35], polymeric materials [36-38] and inorganic
species
[39-41]
have
been
used
as
HTM.
2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamino)-9,9’-spirobifluorene
(spiro-MeOTAD) was the most widely used HTM due to its high thermal stability,
high-quality film formation capability and suitable frontier molecular orbital energy
levels for charge transport [42-43]. In order to achieve high efficiency of pero-SC,
many spiro-MeOTAD derivatives to date have been developed [44-47]. For example,
Seok et al. applied the ortho-substituted derivative of spiro-OMeTAD as HTM and
obtained better performance than the para- and meta-substituted derivatives [48]. Seo
and coworkers used a fluorene-terminated HTM with a fine-tuned energy level and a
high glass transition temperature to ensure highly efficient pero-SC with a
steady-state efficiency of 22.85% [12]. Although high efficiency was achieved with a
dopant via improving the conductivity of HTM, the doping method generally results
in a complicated device fabrication procedure, and also leads to the mismatched
energy levels [49]. In addition, the dopant such as Li-bis(trifluoromethanesulfonyl)
imide (Li-TFSI) can speed up degradation of device performance due to the
deliquescent behavior [35].

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In order to simplify the device fabrication process and reduce the overall device cost,
efficient dopant-free HTM with good charge-carrier transport characteristics was
highly desirable. So far the dopant-free HTM has demonstrated the great potential in
achieving high efficiency pero-SC [50-56]. Jang et al. used novel conjugated
small-molecule based on di(1-benzothieno)[3,2-b:2’,3’-d]pyrrole framework as an
HTM in pero-SC and reported a PCE of 18.09 % [57]. A polythiophene-based
copolymer (PDVT-10) with excellent hole mobility was also used as dopant-free
HTM for a pero-SC, which exhibited a high PCE of 13.4% under 100 mW cm−2
illumination [58].
Herein, we introduced one carbonyl group into spiro-OMeTAD to yield
2,2',7,7'-tetrakis(bis(4-methoxyphenyl)amino)-10'H-spiro[fluorene-9,9'-phenanthren]-
10'-one (spiro-PT-OMeTAD). The introduction of one carbonyl group could increase
the stiffness of the backbone which led to the increase of glass-transition temperature
for Spiro-PT-OMeTAD. Furthermore, the attachment of one carbonyl group to aryl
group could increase conjugation length, which could tune the electronic structure of
the resulting compound. The carbonyl group enhances the hole mobility of
spiro-PT-OMeTAD over the spiro-OMeTAD, and the HOMO energy levels of
spiro-PT-OMeTAD is higher than that of spiro-OMeTAD. When applied as
dopant-free HTM in planar structure photovoltaic device, spiro-PT-OMeTAD-based
perovskite (FA0.85MA0.15Pb(I0.85Br0.15)3) [4, 59-62] solar cell demonstrated power
conversion efficiency of 13.83%, much higher than that for the spiro-OMeTAD-based
device (10.5%).
2. Experimental
General information
All chemicals were purchased from J&K Scientific, Titan, Acros, and Strem
chemicals. Anhydrous solvents were obtained from an Innovative Technology solvent
1
purification system. H NMR spectra were recorded on a Bruker 400 MHz NMR
instrument. Thermogravimetric analysis (TGA) was recorded on a TA SDT 2960
instrument at a heating rate of 10 °C/min under nitrogen. Matrix-Assisted Laser
Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF-MS) was
measured with a BRUKER ultrafleXtreme MALDI-TOF spectrometer. UV–vis
absorption spectra were measured on Cary 60 spectrometer (Agilent Technologies).
PL spectra were recorded on a Hitachi F-4600 fluorescence spectrophotometer. Cyclic

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voltammetry (CV) was carried out on a CHI600 voltammetric analyzer at room
temperature with ferrocenium-ferrocene (Fc+/Fc) as the internal standard. The cyclic
voltammograms were obtained at a scan rate of 100 mV/s. Degassed DCM was used
as solvent for oxidation scan with tetrabutylammonium hexafluorophosphate
(TBAPF6) (0.1 M) as the supporting electrolyte.
Devices Fabrication Process
The FTO substrate was thoroughly cleaned with a sequential sonication treatment in
acetone, ethanol and distilled water, then was dried under nitrogen, and followed by
ultraviolet/ozone treatment for 15 min prior to device fabrication. In this article, the
conventional device structure (FTO/c-TiOx/Perovskite/HTM/Ag electrode) was
applied. Compact TiOx and mixed halide perovskites were prepared according to
related literature [5]. The TiOx precursor was spin coated on top of the FTO substrates
at 4000 rpm for 30 s and then annealed at 450 °C for 45 min. The perovskite precursor
solution (1.2 mol/L, ~50 µL) was spin coated on the top of TiOx firstly at 1000 rpm
for 10 s and secondly at 5500 rpm for 35 s. Then chlorobenzene (100 µL) was added
on the perovskite film. The substrates were annealed at 100 °C for 10 min in glove
box. The hole-transporting materials (70 mmol/L in chlorobenzene, ~50 µL) were
spin-coated on the top of perovskite films. Finally, Ag electrode (~100 nm) was
evaporated on the hole transport layer to complete the device manufacturing process.
We performed the J-V measurement of our unencapsulated devices in an ambient
environment with 40±3% relative humidity. The J-V curves were obtained under
reverse/forward scan, which run at a voltage range from -1.2 to 1.2 V with a scan
speed of 400 mV/s.
Hysteresis indices
The hysteresis indices (HI) of the spiro-OMeTAD and spiro-PT-OMeTAD were
calculated, respectively, with the following formula [63].
ꢂꢃꢄ(ꢅ. ꢆꢇꢈꢉ) − ꢂꢊꢄ(ꢅ. ꢆꢇꢈꢉ)
ꢀꢁ =
ꢂꢃꢄ(ꢅ. ꢆꢇꢈꢉ)
SCLC measurement
Space charge limited current (SCLC) was measured by Mott-Gurney

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equation [64,65]
9
ꢐꢑ
ꢒꢓ
ꢋ = ꢌꢍꢌꢎꢏ
8
where J is the current density, εr is the relative dielectric constant of HTM usually 2-4
for organic semiconductor, herein we use a relative dielectric constant of 3, ε0 is the
permittivity of empty space, µ is the mobility of the HTM, d is the thickness of the
HTM, and V is the internal voltage in the device.
Materials synthesis
2,7-bis(bis(4-methoxyphenyl)amino)-9H-fluoren-9-one
This fluorenone was prepared according literature procedure [66].
2,2',7,7'-tetrakis(bis(4-methoxyphenyl)amino)-10'H-spiro[fluorene-9,9'-phenanthren]-
10'-one (spiro-PT-OMeTAD)
2,7-bis(bis(4-methoxyphenyl)amino)-9H-fluoren-9-one (2.0 g, 3.15 mmol) and
P(OEt)3 (10 mL, 58 mmol) were mixed in a flask (250 mL), then the reaction mixture
was heated to reflux overnight. After cooling down to room temperature, the solvent
was removed under reduced pressure. The residue was purified by column
chromatography (eluent: ethyl acetate/petroleum ether/dichloromethane 1:1:4) to
afford the target material (30%, 1.0 g). 1H NMR (400 MHz, CDCl3) δ (ppm): 7.48 (d,
J = 8.7 Hz, 2H), 7.40 (d, J = 8.9 Hz, 2H), 7.34 (d, J = 2.5 Hz, 2H), 7.03 (d, J = 8.8 Hz,
9H), 6.90 (d, J = 8.8 Hz, 8H), 6.81 (d, J = 8.8 Hz, 8H), 6.74 (d, J = 8.8 Hz, 8H), 6.70
(dd, J = 8.6, 1.9 Hz, 3H), 6.47 (d, J = 1.9 Hz, 2H), 3.77 (s, 14H), 3.71 (s, 10H). MS
(MALDI-TOF ) m/z: 1253.465. Anal. calcd for: C82H68N4O9 (%): C 78.59, H 5.43,
N 4.47; found: 78.11, H 5.83, N 4.34.
3. Results and discussion
The synthetic route of spiro-PT-OMeTAD was depicted in Scheme 1. The
intermediate 2,7-bis(bis(4-methoxyphenyl)amino)-9H-fluoren-9-one was prepared via
Buchwald-Hartwig cross coupling reaction between 2,7-dibromo-fluoren-9-one and
bis(4-methoxy-phenyl)amine. Then the amino functionalized fluorenone reacted with
triethyl phosphite (TEP) to give 2:1 adducts of pentaoxyphosphoranes [67], which
underwent rearrangement to afford the target compound, which was fully
1
characterized with H NMR spectroscopy (Figure S1), MALDI-TOF-MS and
elemental analysis. All the analytical data supports the proposed structure. The

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thermal properties of spiro-PT-OMeTAD were investigated with TGA and DSC
measurement (Figure 1), and it demonstrated good thermal stabilities with the
decomposition temperatures (corresponding to 5% weight loss) of 411ºC and glass
transition temperature (Tg) of 188 ºC. The Tg of spiro-PT-OMeTAD is much higher
than that of spiro-OMeTAD (124 ºC) [68], resulting in better morphological stability.
The UV–vis absorption spectra of spiro-PT-OMeTAD and spiro-OMeTAD were
illustrated in Figure 2. These two compounds both show strong absorption around 380
nm. It’s notable that spiro-PT-OMeTAD exhibits a weak absorption in the range of
400-500 nm, which would be attributed to intramolecular charge transfer from the
substituted fluorene fragment to phenanthrenone unit. So spiro-PT-OMeTAD will not
obstruct sunlight from efficiently reaching the active layer in the solar cells, and
spiro-PT-OMeTAD has a narrower bandgap of 2.24 eV in comparison with that of
spiro-OMeTAD (2.96 eV), which are determined by their absorption onset.
The electrochemical properties of spiro-PT-OMeTAD were studied with cyclic
voltammetry (CV) measurement to determine its frontier molecular orbital energy
levels (Figure S2). The first oxidation potential is slightly lower for
spiro-PT-OMeTAD than for spiro-OMeTAD, indicating that spiro-PT-OMeTAD has
higher HOMO energy level, which is due to the spatial π-orbital overlap between
fluorene and carbonyl group in spiro-PT-OMeTAD [69]. The HOMO levels of
spiro-PT-OMeTAD and spiro-OMeTAD are determined to be -4.70 eV and -4.84 eV,
respectively, with the reference ferrocene/ferrocenium couple at -4.8 eV vs vacuum.
The LUMO energy levels are estimated with the difference between the HOMOs and
the optical bandgap (Table 1). Considering that spiro-PT-OMeTAD contains one
additional C=O group, it’s reasonable that spiro-PT-OMeTAD (-2.46 eV) has lower
LUMO than spiro-OMeTAD (-1.90 eV). Nevertheless, it is sufficiently high to
prevent electron back-transfer from the cathodic electrode to the perovskite.
In order to understand the photophysical properties of these two HTMs, density
functional theory (DFT) calculations were performed to simulate the frontier
molecular orbital spatial distributions at a B3LYP/6-31G(d) level (Figure 3). For
spiro-OMeTAD, the HOMO is mainly distributed on the bis(4-methoxyphenyl)amine
group and partially on fluorene unit, and its LUMO is distributed on fluorene unit.
While the HOMO of spiro-PT-OMeTAD is localized in the substituted fluorene unit,
and its LUMO is localized in phenanthrenone group. So these two compounds show
similar HOMO energy levels, but different LUMO energy levels. The intrinsic

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electron-withdrawing property of phenanthrenone helps us to explain the observation
of lower LUMO of spiro-PT-OMeTAD. Thus the DFT calculation results were
consistent with their photophysical properties and CV data.
In order to evaluate the performance of spiro-PT-OMeTAD as HTM for perovskite
solar cells, dopant-free devices (Figure 4) with
a
configuration of
FTO/TiOx/perovskite (FA0.85MA0.15Pb(I0.85Br0.15)3)/HTM/Ag [5] were fabricated,
where MA was methylammonium and FA was formamidinium. The devices based on
spiro-OMeTAD were also built for comparison purpose. The J-V characteristics under
standard 1 sun illumination and external quantum efficiency (EQE) spectra are shown
in Figure 5, and the photovoltaic parameters are summarized in Table 2. The device
based on spiro-PT-OMeTAD exhibited higher PCE of 13.83% (VOC = 0.99 V, JSC
=
22.36 mA cm−2, FF = 0.62) under the reverse scan direction than that based on
spiro-OMeTAD (10.5%, VOC = 1.02 V, JSC = 21.78 mA cm−2, FF = 0.47) under
parallel condition. The current density–voltage curves under forward scan direction
were shown in Figure S3 and the device parameters are summarized in Table S1. It’s
worth noting that the Jsc value obtained from integrating the external quantum
efficiency (EQE) curves is in good agreement with the measured one (Figure 5b). The
overall PCE enhancement is mainly attributed to the improvement in JSC and FF. To
elucidate and illustrate the FF enhancement, the hole-transport properties of
spiro-PT-OMeTAD
and
spiro-OMeTAD
were
investigated
by
a
space-charge-limited-current (SCLC) analysis with device configuration of
glass/ITO/PEDOT:PSS/HTL/MoO3/Ag. The SCLC mobility (Figure 6) was calculated
by Mott-Gurney equation. The hole mobility of spiro-PT-OMeTAD and
Spiro-OMeTAD is estimated to be 3.84×10-4 cm2 V-1 s-1 and 1.28×10-4 cm2 V-1 s-1,
respectively. In order to further the understanding of FF enhancement, the film
morphology
of
perovskite,
perovskite/Spiro-OMeTAD
and
perovskite/Spiro-PT-OMeTAD was studied by AFM, and the roughness of these three
films was 36.18 nm, 10.06 nm and 9.13 nm, respectively (Figure S4). The uniform
morphology usually benefits the charge transfer at the interface and produces less
pin-holes and current leakage, thus leading to better device performance. This result
indicates that spiro-PT-OMeTAD could efficiently conduct the hole and suppress
charge recombination.
To determine the origin of the charge extraction properties of spiro-PT-OMeTAD, the
interfacial charge transfer capabilities of the perovskite/spiro-PT-OMeTAD were

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investigated by the steady-state photoluminescence (PL) measurement. As shown in
Figure 7, when the perovskite film was coated with HTMs, its PL emission was
significantly quenched due to electron transfers from the HOMO of HTMs to the
excited state of perovskite [70]. Spiro-PT-OMeTAD exhibited a better quenching than
spiro-OMeTAD due to its well-matched energy levels and a more efficient hole
transfer between the perovskite and the phenanthrenone-based HTMs. In order to
more study the hole transfer at the interface, we have measured the
photoluminescence lifetime of perovskite with different HTMs on top, and the
relevant data are shown in Figure S5. The photoluminescence lifetime of the pure
perovskite layer was 22.89 ns. When the HTM was deposited on the perovskite layer,
photo-generated electron-hole pairs were separated between perovskite and HTM, and
the holes was transferred to the HTL to reduce the electron-hole pair recombination.
The lifetimes were reduced to 4.79, and 4.52 ns for spiro-OMeTAD-coated and
spiro-PT-OMeTAD-coated perovskite layers, respectively. So there is more efficient
charge extraction with spiro-PT-OMeTAD as HTMs. Furthermore, the devices
based on spiro-PT-OMeTAD exhibited low hysteresis. The hysteresis indices (HI) of
the spiro-OMeTAD and spiro-PT-OMeTAD were estimated to be 0.0850, and 0.0505.
The improved JSC and FF values and the negligible hysteresis observed in
spiro-PT-OMeTAD-based device indicate the excellent hole transportation and less
charge accumulation at the perovskite/spiro-PT-OMeTAD interface [71].
4. Conclusion
In conclusion, a novel HTM (i.e. spiro-PT-OMeTAD) was designed and synthesized
by the introduction of one carbonyl group into spiro-OMeTAD. The CV measurement
and DFT calculation indicated these two compounds had similar HOMO energy levels
but different LUMO energy levels. The SCLC studies revealed that
spiro-PT-OMeTAD showed better hole transfer properties than spiro-OMeTAD. The
steady-state PL measurement suggested that an efficient charge transfer occurred at
the perovskite/spiro-PT-OMeTAD interface. As a result, dopant-free perovskite solar
cells based on spiro-PT-OMeTAD exhibited better device performance than
spiro-OMeTAD. It was clear that the introduction of one carbonyl group into
spiro-PT-OMeTAD led to a great enhancement in device efficiency. The present
results and findings may provide new insights for the design of novel and efficient
HTMs.

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Acknowledgements
We thank to the financial support from the National Key R&D Program of China
(2016YFB0400703), the National Natural Science Foundation of China (21472135)
and Natural Science Foundation of Jiangsu Province of China (BK20151216). This
project is also funded by Collaborative Innovation Center of Suzhou Nano Science
and Technology (CIC-Nano), Jiangsu Key Laboratory for Carbon-Based Functional
Materials & Devices, Soochow University and by the Priority Academic Program
Development of Jiangsu Higher Education Institutions (PAPD), Key Research and
Development Plan of Shaanxi Province (2017ZDCXL-GY-06-03), Special Scientific
Research Plan of Shaanxi Provincial Education Department (17JK0095).
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Scheme 1. Synthetic routes of Spiro-PT-OMeTAD.

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Spiro-PT-OMeTAD
Spiro-PT-OMeTAD
1.0
0.8
0.6
0.4
0.2
0.0
411oC
188 o
C
150
200
200
300
400
500
600
Temperature (oC)
(o
Temperature
C)
Fig 1. The TGA curve (left) and DSC curve (right) of Spiro-PT-OMeTAD at a
heating rate of 10 oC /min under N2.

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Spiro-PT-OMeTAD
Spiro-OMeTAD
1.0
0.8
0.6
0.4
0.2
0.0
300
400
500
600
Wavelength (nm)
Fig 2. UV–Vis spectra of Spiro-PT-OMeTAD and Spiro-OMeTAD in DCM at room
temperature.

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Fig 3. Theoretically calculated spatial distributions and energies of the HOMO and
LUMO levels of Spiro-OMeTAD and Spiro-PT-OMeTAD as well as their values of
Eg.

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Table 1. Summary of Optical and electrochemical properties of the Spiro-OMeTAD
and Spiro-PT-OMeTAD
HTM
λmax
Td [oC]
Tg [oC]
HOMO LUMO Eg
[nm]
[eV]
-4.70
-4.84
[eV]
-2.46
-1.90
[eV]
2.24
2.96
Spiro-PT-OMeTAD 376.9 411
Spiro-OMeTAD 386.7
188
124
449
Tg = glass-transition temperature.
Td = temperature for 5% weight loss.
Eg = energy gap calculated from the onset absorption wavelength.
HOMO is estimated by cyclic voltammetry, and LUMO is deduced from Eg and
HOMO.

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Fig 4. a) Energy level diagram of the device with Spiro-PT-OMeTAD as the HTM; b)
Scheme
diagram
of
the
device
structure
(FTO/c-TiOx/FA0.85MA0.15Pb(I0.85Br0.15)3/HTM/Ag).

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Fig 5. a) Current density–voltage characteristics pristine Spiro-OMeTAD and pristine
Spiro-PT-OMeTAD. b) EQE spectra for the devices with pristine Spiro-OMeTAD and
pristine (dopant free) Spiro-PT-OMeTAD as HTMs.
Table 2. Summary of photovoltaic parameters of dopant-free devices based on
Spiro-PT-OMeTAD and Spiro-OMeTAD
HTM
Voc [V]
0.99
Jsc [mA/cm2]
FF
PCE [%]
13.83
Spiro-PT-OMeTAD
Spiro-OMeTAD
22.36
0.62
0.47
1.02
21.78
10.5

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100
10
1
Spiro-PT-OMeTAD
Spiro-OMeTAD
Fit of Spiro-PT-OMeTAD
Fit of Spiro-OMeTAD
0.1
0.01
0
2
3
1V
appl bi
-V (V)
Fig 6. The hole mobility measurement of HTMs from the SCLC J–V characteristics
obtained in the dark for hole-only devices.

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80k
70k
60k
50k
40k
30k
20k
10k
0
Perovskite/Spiro-OMeTAD
Perovskite/Spiro-PT-OMeTAD
Perovskite
700
750
800
850
Wavelength (nm)
Fig 7. Steady-state PL spectra of perovskite films, and perovskite films coated with
spiro-OMeTAD and with spiro-PT-OMeTAD

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Table of Contents
The introduction of one carbonyl group into HTM led to a great improvement in
dopant-free device performance with PCE enhanced from 10.50% to 13.83%.

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Highlights
The insert of carbonyl group increased structural rigidity and glass-transition
temperature.
The introduction of carbonyl group into Spiro-PT-OMeTAD gave an increase in hole
mobility.
The small roughness of perovskite/Spiro-PT-OMeTAD film led to improved device
performance.