Regulating Surface Termination for Efficient Inverted Perovskite Solar Cells with Greater Than 23% Efficiency

Article abstract of DOI:10.1021/jacs.0c09845

Passivating surface and bulk defects of perovskite films has been proven to be an effective way to minimize nonradiative recombination losses in perovskite solar cells (PVSCs). The lattice interference and perturbation of atomic periodicity at the perovskite surfaces often significantly affect the material properties and device efficiencies. By tailoring the terminal groups on the perovskite surface and modifying the surface chemical environment, the defects can be reduced to enhance the photovoltaic performance and stability of derived PVSCs. Here, we report a rationally designed bifunctional molecule, piperazinium iodide (PI), containing both R2NH and R2NH2+ groups on the same six-membered ring, behaving both as an electron donor and an electron acceptor to react with different surface-terminating ends on perovskite films. The resulting perovskite films after defect passivation show released surface residual stress, suppressed nonradiative recombination loss, and more n-type characteristics for sufficient energy transfer. Consequently, charge recombination is significantly suppressed to result in a high open-circuit voltage (VOC) of 1.17 V and a reduced VOC loss of 0.33 V. A very high power conversion efficiency (PCE) of 23.37% (with 22.75% certified) could be achieved, which is the highest value reported for inverted PVSCs. Our work reveals a very effective way of using rationally designed bifunctional molecules to simultaneously enhance the device performance and stability.

Full text of DOI:10.1021/jacs.0c09845

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Article
Regulating Surface Termination for Efficient Inverted Perovskite
Solar Cells with Greater Than 23% Efficiency
Fengzhu Li,∇ Xiang Deng,∇ Feng Qi, Zhen Li, Danjun Liu, Dong Shen, Minchao Qin, Shengfan Wu,
Francis Lin, Sei-Hum Jang, Jie Zhang, Xinhui Lu, Dangyuan Lei, Chun-Sing Lee, Zonglong Zhu,*
and Alex K.-Y. Jen*
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ABSTRACT: Passivating surface and bulk defects of perovskite films has
been proven to be an effective way to minimize nonradiative recombination
losses in perovskite solar cells (PVSCs). The lattice interference and
perturbation of atomic periodicity at the perovskite surfaces often
significantly affect the material properties and device efficiencies. By tailoring
the terminal groups on the perovskite surface and modifying the surface
chemical environment, the defects can be reduced to enhance the
photovoltaic performance and stability of derived PVSCs. Here, we report
a rationally designed bifunctional molecule, piperazinium iodide (PI),
containing both R2NH and R2NH2+ groups on the same six-membered ring,
behaving both as an electron donor and an electron acceptor to react with
different surface-terminating ends on perovskite films. The resulting perovskite films after defect passivation show released surface
residual stress, suppressed nonradiative recombination loss, and more n-type characteristics for sufficient energy transfer.
Consequently, charge recombination is significantly suppressed to result in a high open-circuit voltage (VOC) of 1.17 V and a
reduced VOC loss of 0.33 V. A very high power conversion efficiency (PCE) of 23.37% (with 22.75% certified) could be achieved,
which is the highest value reported for inverted PVSCs. Our work reveals a very effective way of using rationally designed
bifunctional molecules to simultaneously enhance the device performance and stability.
of the surface energy, vacant terminations are more stable than
those from PbI2 flat and methylammonium iodide/formamidi-
nium iodide (MAI/FAI) terminations, which can induce many
vacancy defects (such as VI and VMA/VFA) on the surface.14 The
larger FA+ with a smaller dipole moment has a weaker
interaction with the [PbI6]2− octahedral than does MA+.
Thereby, the antisite PbI defects are formed more easily in
FA+-dominant OIHPs with lower formation energies on the
surface than in bulk, which may cause deep-level defects such as
Pb clusters (i.e., Pb2+ dimers).15
Recently, an enormous amount of effort has been devoted to
suppressing the nonradiative recombination loss in order to
further enhance the open-circuit voltage (VOC) and PCE by
passivating positive Pb2+ traps and negative halide traps.16−20
Various molecules have been developed either as electron
donors or as electron acceptors for passivating positively and
negatively charged traps.21−30 Among them, Lewis acids such as
INTRODUCTION
■
Organic−inorganic metal halide perovskite solar cells (PVSCs)
have gained enormous attention during the past few years owing
to their superb semiconducting properties, relatively simple and
easy processing, low cost, and rapidly ascending power
conversion efficiencies (PCEs) reaching as high as 25.5%.1−10
However, the champion PCE of PVSC is still below that
predicted from the theoretical Shockley−Queisser (S−Q) limit,
mainly due to the loss from nonradiative recombination. Unlike
the robust perovskite oxides, the frail Coulombic interaction and
weak ionic bonding of organic−inorganic halide perovskites
(OIHPs) cause more vulnerable atomic reorganization and
deviations on the derived film surface.11 The crystal lattice
interference and atomic periodicity perturbation at the surface of
OIHPs alter the electronic behavior and band structure,
generating a considerable number of nonradiative recombina-
tion centers. Such behaviors are more prominent at the surface
than in the bulk of OIHP films, which will significantly affect the
perovskite material properties and device performance.12,13
However, originating from the various surface terminations
and undercoordinated sites, surface defects are notably different
from those formed in the bulk of OIHPs. The undercoordinated
Pb2+ and halide sites are the predominant trap sources on
surfaces that cause nonradiative recombination losses. In terms
Received: September 14, 2020
https://dx.doi.org/10.1021/jacs.0c09845
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© XXXX American Chemical Society
A

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Figure 1. Simulated PXRD of (a) (PI)2PbI2·2DMSO and (b) (PDI)2PbI2. Insets are the optical microscopy images. Crystal structures of (c)
(PI)2PbI2·2DMSO and (d) (PDI)2PbI2. 1H NMR spectra in d6-DMSO of (e) PI and PI + PbI2 and (f) PDI and PDI + PbI2.
carboxylic acid and phosphoric acid, sulfonic groups, and
ammonium groups can neutralize undercoordinated halides
through coordinate bonding to form Lewis adducts. On the
other hand, Lewis bases, such as carboxylate and amine groups,
and electron-rich aromatic structures have been reported to
reduce undercoordinated lead ions and/or lead clusters by
donating a lone pair of electrons.
Although numerous molecules have been developed to tailor
the surface chemical environments and surface defects, most of
them can only passivate either the positively or negatively
charged defects. There are very few molecules that can passivate
both Pb2+ and halide ion traps on the perovskite surface.21,28 To
achieve enhanced passivation effects, the ability to introduce
stronger binding action between the passivator and perovskite to
form an ionic bond and a stable chemical interaction is critical.
Therefore, it is essential to develop multifunctional molecules
that can passivate both positively and negatively charged defects
with simple solution treatments to further enhance the device
performance.
Here, we report the development of a novel bifunctional
molecule, piperazinium iodide (PI), containing both an R2NH
and an R2NH2+ group on the same six-membered ring with an
in-plane dipole that is capable of functioning as an electron
donor and an electron acceptor to react with different surface
terminating groups. It was found that PI could form a Pb−N
bond in the single crystal of (PI)2PbI2·2DMSO, which was
grown as a model compound to investigate the chemical
interactions between PI and PbI2. After introducing PI for
surface treatment, the residual stress of the film surface could
also be released. The tuning of surface termination with PI
treatment also helps to achieve a more n-type characteristic film
to facilitate charge transfer. The combined effects resulted in
suppressed nonradiative recombination loss and a significantly
reduced VOC loss of 0.33 V with a very low ΔV3 of 60.13 mV.
The PCE of inverted (p-i-n) devices achieved 23.37% (with
22.75% certified) with a VOC of 1.17 V, which is the highest value
for inverted PVSCs to date.
RESULTS AND DISCUSSION
■
To demonstrate the specific interaction of different functional
groups (neutral R2NH and the R2NH2+ cation) in PI, we have
+
also synthesized piperazinium diiodide (PDI) with two R2NH2
cations for comparison. The detailed synthesis is summarized in
the Supporting Information (SI). The (PI)2PbI2·2DMSO
(CCDC 1935315) and (PDI)2PbI2 (CCDC 2009125) single
crystals were grown using the reported antisolvent vapor-
assisted crystallization method.31 Detailed crystal data and the
refinement of (PI)2PbI2·2DMSO and (PDI)2PbI2 are listed in
Table S1, and the corresponding structures are shown in Figure
1. The rod-like translucent (PI)2PbI2·2DMSO single crystals are
millimeter-sized and have a 1D chain organic−inorganic hybrid
structure (Figure 1a). The lone-pair electrons of the R2NH on
PI replace a halide to bond with Pb to form a Pb−N bond with a
bond length of 2.80 Å, indicating a strong chemical interaction
between Pb2+ and the lone pair of the neutral R2NH group
(Figure 1c). Surprisingly, different from the 3D structure of
MAPbI3 or FAPbI3, (PDI)2PbI2 single crystals possess a 0D
organic−inorganic hybrid structure in which the metal halide
ions (PbI64−) are completely isolated from each other and
surrounded by the piperazinium organic cations (Figure 1d).
The interactions of PI and PDI with PbI2 in the two model
compounds are further explored with 1H NMR spectrometry. As
shown in Figure 1e, the fast proton exchanges among NH,
HDO, and DMSO induce the weak signal of H from NH or
B
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Figure 2. High-resolution XPS spectra of corresponding perovskite films: (a) C 1s spectra, (b) N 1s spectra, and (c) Pb 4f spectra.
Figure 3. (a−c) Two-dimensional GIWAXS patterns and (d) the grazing incidence X-ray diffraction (GIXRD) spectrum of the corresponding
perovskite films with an incident angle of 0.2°. * denotes PbI2. (e−g) GIXRD spectrum at different tilt angles for the reference film and PI- and PDI-
treated films, respectively. (h) Residual strain of the corresponding perovskite films’ diffraction strain data as a function of sin2 φ. All of the perovskite
films are deposited on an ITO substrate.
during testing.34 The peak area of CO shows a visible decrease
after PI and PDI treatments, which indicates the suppressed
oxidation process and improved film stability.35 In the N 1s XPS
spectrum, the featured bonds of C−N (400.7 eV) and CNH2+
(402.4 eV) from FA+/MA+ in the reference film slightly shift to
lower binding energies (400.5 and 402.2 eV, respectively) after
PI treatment (Figure 2b). This shift may originate from the
formation of hydrogen bonds N−H···N between the FA+/MA+
and the R2NH from PI.36 However, there is no peak shift in the
N 1s spectrum after PDI treatment, which helps to differentiate
the unique function of PI with the R2NH group. The new peaks
appearing at 285.4 eV in the C 1s spectrum and at 399.8 eV in
the N 1s spectrum are attributed to the C bonds to neutral N
(C−NH−C) and neutral N in PI, respectively.37 These peaks
further verify the existence of PI. In the Pb 4f spectrum, the
binding energies at 143.3 and 138.4 eV are assigned to 4f5/2 and
4f7/2 of divalent Pb2+, respectively. And the two shoulder peaks
+
NH2 in the PI sample. However, after mixing PbI2 and PI in
solvent, the strong interaction between R2NH and Pb2+
surpasses proton exchange to give a more well-defined
signal.32,33 On the other hand, the H NMR spectrum of PDI
1
shows less difference upon addition of PbI2 (Figure 1f). These
results help to confirm the distinctive interaction induced by the
neutral R2NH on PI, which has not been reported before.
To investigate the potential interactions of PI and PDI with
the perovskite film surface, the materials were deposited via spin
coating (1 mg/mL in dry isopropanol) on the perovskite film
with a composition of Cs0.05(FA0.95MA0.05)0.95Pb(I0.95Br0.05)3.
High-resolution X-ray photoelectron spectroscopy (XPS) was
performed as shown in Figure 2. In the C 1s XPS spectrum, the
binding energies (BEs) at 284.8, 286.5, and 288.4 eV are
assigned to C−C, CNH2+, and CO, respectively (Figure
2a). Oxidized carbon species may originate from the decay of the
perovskite film when exposed to the ambient environment
C
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Figure 4. (a) Steady-state PL spectra and (b) time-resolved photoluminescence plots of perovskite films. Confocal photoluminescence (PL) intensity
maps of (c) reference perovskite film and perovskite films with (d) PI and (e) PDI treatments. The contour in the pictures represents the auto level of
PL intensity, with the sequence of blue, purple, magenta, red, green, and cyan.
at 141.6 and 136.6 eV at lower BE are associated with metallic
Pb0 (Figure 2c). These peaks move to higher binding energy by
more than 400 meV only after PI treatment (centered at 143.8
and 138.9 eV) in terms of bond formation with the R2NH in PI,
which is in line with the single-crystal studies.32,38 In addition,
the peak area of Pb0 decreased significantly after both PI and
PDI treatments. Pb0 is an indication of the existence of iodide
and cation vacancies on the perovskite film, which can be
inhibited by the surface treatments of both PI and PDI.39
Besides, electron donor R2NH in PI interacts strongly with
undercoordinated Pb2+ as implied by the single-crystal results,
contributing to the greatly decreased Pb0 peak after PI
treatment.
Grazing-incidence wide-angle X-ray scattering (GIWAXS)
characterization at an incident angle of 0.2° was also carried out
to explore the surface crystallite structure of perovskite films
after PI and PDI treatments. As shown in Figure 3a−c, the
GIWAXS patterns of films treated with PI and PDI show higher
intensities along the (101) ring (|q| = 0.95−1.08 Å−1), which
indicates better crystallinity compared to that of the reference
film. There are no new peaks that emerge after either PI or PDI
treatment. However, excessive PbI2 in the position at |q| = 0.88−
0.94 Å−1 disappeared only after PI treatment (Figures S5 and
S6). This result is consistent with the measurements from
grazing incidence X-ray diffraction (GIXRD) at an incident
angle of 0.2° (Figure 3d). The PbI2 signal that decreased only
after PI treatment indicates a strong interaction, which is in line
with the single-crystal structure and XPS results.
negative slope of the fitting line indicates tensile stress that exists
at the perovskite film. As shown in Figure 3h, the residual tensile
strain gradually decreases from 61.57
6.92 MPa for the
reference film to 27.54 2.16 and 40.15 3.89 MPa after PI
and PDI treatments, respectively. This shows that the defect
passivation in the A-site vacancy and in undercoordinated Pb2+
with R2NH2+ and R2NH groups results in lower surface residual
+
stress. After surface treatment with PI, the R2NH2 group can
insert the A-site vacancy and the R2NH group can react with the
undercoordinated Pb2+, thus regulating the surface termination
and releasing the surface residual stress, which can play an
important role in carrier dynamics and device performance.41,42
To understand more about the passivation effect of PI, the
recombination occurring in the perovskite films was investigated
by steady-state PL and time-resolved photoluminescence
(TRPL) analysis. As shown in Figure 4a, the PL intensities of
perovskite films after PI and PDI treatments are about 5 and 3
times higher than those of the reference films, suggesting that
their nonradiative recombination loss is alleviated considerably
after surface passivation. The TRPL decay curves (Figure 4b)
were fitted with biexponential function I(t) = A1 exp(−t/τ1) +
A2 exp(−t/τ2), where τ1 and τ2 are the fast and slow decay
components, respectively (Tables S2 and S3). The average
n
∑
Aiτ2
i
i=1
lifetime (τavg) can be calculated with τ
=
. We found
n
i=1
avg
∑
Aiτ
i
that the perovskite films after PI and PDI surface treatments
possessed a longer carrier lifetime compared to that of the
reference film. The τavg values of the reference perovskite film
and PI- and PDI-treated films are 305, 1948, and 1461 ns,
respectively. The significantly prolonged lifetimes of perovskite
films after PI and PDI treatments are attributed to the
suppressed defects such as lead clusters, undercoordinated
halides, and Pb−I antisite which usually cause nonradiative
To investigate the effects of PI and PDI treatments on the
surface crystal structure, we employed the GIXRD technique
with the 2θ−sin2 φ method to analyze the residual stress on the
film surface.40,41 The (012) plane at 31.6° was chosen as the
target because of its diversity in providing more grain
information and a dilute orientation effect on the linear
relationship of 2θ−sin2 φ in the GIXRD measurements. Figure
3e−g shows that the scattering peaks gradually shift to the left by
varying φ from 10 to 60° at different levels. The film stress can be
calculated by fitting 2θ as a function of sin2 φ, in which the
recombination.43 The combined effects of R2NH and R2NH2
+
groups on PI for defect passivation are superior to those
+
obtained from PDI with only the R2NH2 group, which
demonstrates the benefit of having multifunctional passivators.
The trap density (Ntrap) was calculated with space-charge-
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Figure 5. (a) Device structure of the inverted PVSCs. (b) Current density−voltage (J−V) characteristics of devices with and without surface
treatments. (c) Statistics of PCE distribution for PVSCs with and without PI treatment. (d) J−V curves of the PI-treated device with different scan
directions (forward, 1.2 to −0.1 V; reverse, −0.1 to 1.2 V). (e) External quantum efficiency (EQE) spectra of the champion device with PI treatment.
(f) Stabilized power output of a PI-treated device tracked at the maximum power point (MPP) under AM 1.5G illumination.
limited-current (SCLC) method (Figure S8). The Ntrap of the
reference film based on the hole-only device is about 2.54 × 1016
cm−3. After the passivation with PI and PDI, the Ntrap was
reduced to 8.4 × 1015 and 1.64 × 1016 cm−3, respectively. The
lower Ntrap after PI treatment demonstrates the effectiveness of
defect passivation by PI compared to that by PDI, which is
consistent with the PL and TRPL results.
bending between the perovskite and the electron-transporting
layer, which can facilitate more efficient charge transfer.
To verify the passivation effect of PI on photovoltaic
performance, the devices were fabricated with a configuration
of ITO glass/PTAA/perovskite/C60/bathocuproine (BCP)/Ag
as shown in Figure 5a. The reference device without passivation
showed a PCE of 20.76% (average PCE: 19.67%) with an open-
circuit voltage (VOC) of 1.06 V, a short-circuit current density
(JSC) of 24.93 mA cm−2, and a fill factor (FF) of 78.57% under 1
sun illumination (AM 1.5G, 100 mW cm−2) (Figure S12 and
Table S4). The PCE of the devices after PDI treatment was
improved to 21.98% (average PCE: 21.31%), benefiting from
the enhanced VOC (1.13 V) due to the passivated A-site vacancy
Confocal photoluminescence (PL) mappings were also
conducted to explore the optoelectronic properties of perovskite
films as displayed in Figure 4c−e. The PL intensity in the central
area of a single grain is much higher than those from the grain
boundaries, which indicates better charge transfer with
minimized recombination. After PI treatment, the overall PL
intensity is significantly improved and the intensity distribution
is more homogeneous compared to those obtained from the
reference and PDI-treated films. The PL peak position
distribution of the films was counted, and the PL peak histogram
of the films was demonstrated in Figures S9 and S10. The
distribution of PL peaks on the perovskite film is considerably
narrowed after PI treatment, suggesting that the surface phase
segregation is suppressed. A more homogeneous film is
favorable for charge transfer because the energy loss during
the transfer between domains can be significantly reduced.44,45
Ultraviolet photoelectron spectroscopy (UPS) was employed
to analyze the electronic structures of perovskite films after PI
treatment. The valence band maximum (EV) shifts by 180 meV
toward the vacuum level (EVAC), while the EF shifts by 350 meV
toward the conduction band minimum (EC) after treatment
(Figure S11). This EF shift indicates that the PI-treated films
demonstrate more n-type characteristics, which is probably due
to the changed surface termination.46,47 The PbI2 termination
has been reported to have deeper energy levels than those of the
MA+/FA+ terminations.48 After introducing PI onto the film
surface, the dipole in PI orients away from the surface, exposing
electropositive ammonium terminal groups and enabling band
+
defects by the R2NH2 group (Figure 5b). However, JSC
decreased, perhaps due to the possible formation of lower-
dimensional perovskites, which inhibited charge transport. On
the contrary, the devices after being treated with PI achieved a
significantly enhanced PCE of 23.37% (VOC of 1.17 V, FF of
80.17%, JSC of 24.92 mA cm−2) (average PCE: 22.26%) with
negligible hysteresis as shown in Figure 5c,d. The device
performance was validated by an independent certification
laboratory to show a high PCE of 22.75% with a JSC of 24.68 mA
cm−2, a VOC of 1.16 V, and an FF of 79.16% (Figure S13). This is
the highest certified PCE for inverted PVSCs to date. The
external quantum efficiency (EQE) was measured as shown in
Figure 5e. The integrated photocurrent of the champion device
with 24.18 mA cm−2 matched well with the values obtained from
the J−V curves.
Figure 5f exhibits the stabilized power output at the maximum
power point (MPP) for the PI-treated champion device under
continuous AM 1.5G illumination. The stabilized PCE is
22.88%, which is in good agreement with the PCE obtained from
the J−V curves. The greatly improved PCE is mainly attributed
to the highly enhanced VOC from 1.06 to 1.17 V due to PI
passivation. The VOC loss is significantly reduced to 0.33 V,
E
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Figure 6. (a) Highly sensitive external quantum efficiency (EQE) spectra of the corresponding devices. (b) EQE of EL and the EL spectra of the
champion device with PI treatment. (c) VOC loss analysis of the corresponding devices.
which is among the lowest values in PVSCs reported so far
(Figure S14). Moreover, the PI passivation not only enhanced
the device performance but also improved its stability. The
encapsulated device could maintain 93% of its initial efficiency
under humid air (RH 55 5%, 25 °C), while the efficiencies of
the reference device degraded to 40% of its original values. Also,
the PI-treated device can maintain over 98% of its initial
efficiency while that of the reference device decreased to 87% of
its initial efficiency under continuous illumination at 200 h.
In order to quantitatively analyze the impact of PI and PDI
treatments on VOC loss, we employed the detailed balance
theory to calculate the VOC loss:49−51
where kB is the Boltzmann constant and EQEEL is the EQE of
electroluminescence (EL). The EQEEL values were collected by
using the PVSCs as light-emitting diodes (LEDs) (Figure 6b and
Figure S17). The EQEEL of the reference device is 0.55%, which
can be converted to a ΔV value of 134.35 mV. The ΔV value of
3
3
the PI-treated device was reduced significantly to 60.13 mV with
an EQEEL of as high as 9.77%. Such a low value is among the
smallest energy losses of photovoltaic devices, further proving
the excellent passivating effect of PI on reducing the
nonradiative recombination loss.54 The VOC loss analysis of
ΔV , ΔV , and ΔV is shown in Figure 6c and Table S5. Thus, a
1
2
3
considerably reduced VOC deficit of 0.33 V could be achieved,
which is among the lowest values reported so far.
qΔV = Eg − qVOC
CONCLUSIONS
■
SQ
rad
nonrad
OC
= (Eg − qV + qVOSQC ) + ΔqV + ΔqV
OC
OC
We have demonstrated a very effective way to passivate the
surface defects of perovskites using a bifunctional molecule
containing both R2NH2+ and R2NH groups on a six-membered
ring to improve both the efficiency and stability of inverted
PVSCs. The (PI)2PbI2·2DMSO single crystal was grown as a
model compound to mimic the interactions between PI and
perovskite surface defects. The PI molecule with an R2NH
electron donor and an R2NH2+ electron acceptor forms a dipole
to reduce residual stress and suppress nonradiative recombina-
tion loss in perovskites to boost the efficiency of inverted PVSCs
to a very high value of 23.37% (with 22.75% certified) and a
reduced VOC deficit of 0.33 V. This work paves a new way for
using rationally designed molecular passivators to reduce the
surface defects of perovskite films and further improve the
efficiency and stability of derived PVSCs.
= (Eg − qVOSQC ) + (qV − qVOraCd) + (qV − qVOC)
SQ
OC
rad
OC
= q(ΔV + ΔV + ΔV )
1
2
3
Here, q is the elementary charge, ΔV is the overall voltage loss,
Eg is the perovskite band gap, V
limit of VOC, VOraCd refers to the VOC in which only radiative
recombination occurred in PVSCs, ΔV is the VOC loss caused
by the nonideal EQE above the band gap, ΔV is the VOC loss
SQ
OC
is the Shockley−Queisser
SQ
OC
rad
OC
nonrad
OC
of the sub-band-gap radiative recombination, andΔV
is the
VOC loss of nonradiative recombination. According to the
theory, VOC loss consists of three parts, ΔV , ΔV , and ΔV . ΔV
1
2
3
1
comes from the radiative recombination above Eg. The
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.0c09845.
reference and PI- and PDI-treated PVSCs have similar ΔV
1
■
sı
values of 265.15, 264.61, and 265.11 mV, respectively.
ΔV results from the energy loss from blackbody radiation,
2
where the EQE of PVSCs extend into the region below Eg. It can
be computed through the highly sensitive EQE (Figure 6a).52,53
Details concerning synthesis, device production, and
characterization methods (PDF)
Single-crystal structure of (PI)2PbI2·2DMSO (1935315)
(CIF)
The calculated ΔV values are 27.37, 2.73, and 12.46 mV for the
2
reference and the PI- and PDI-treated devices, respectively. The
peaks appearing in the region of 1.25−1.35 eV in the highly
sensitive EQE spectra demonstrate that the photocurrent
contributed to shallow trap states as reported before.20,22 ΔV3
is the voltage loss mainly owing to the nonradiative
recombination, being expressed by the following equation
Single-crystal structure of (PDI)2PbI2 (2009125) (CIF)
AUTHOR INFORMATION
Corresponding Authors
■
Zonglong Zhu − Department of Chemistry, City University of
Hong Kong, Kowloon, Hong Kong; orcid.org/0000-0002-
8285-9665; Email: zonglzhu@cityu.edu.hk
kBT
q
ΔV =
ln(EQEEL)
3
F
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Alex K.-Y. Jen − Department of Materials Science and
Engineering and Department of Chemistry, City University of
Hong Kong, Kowloon, Hong Kong; Department of Materials
Science & Engineering, University of Washington, Seattle,
Washington 98195, United States; orcid.org/0000-0002-
9219-7749; Email: alexjen@cityu.edu.hk
Guangdong Major Project of Basic and Applied Basic Research
(no. 2019B030302007), the Air Force Office of Scientific
Research (FA9550-18-1-0046), and a Teaching Start-Up Grant
of the City University of Hong Kong (6000672). Z.Z. and A.J.
are grateful for the technical support provided by Mr. Shekman
Yiu for single-crystal analysis.
Authors
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■
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Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.0c09845
Author Contributions
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Defects of Perovskite Solar Cell Absorbers: A First−Principles Study. J.
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∇F.L. and X.D. contributed equally to this work.
Notes
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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■
This work was supported by APRC Grants of the City University
of Hong Kong (9380086 and 9610421), Innovation and
Technology Bureau supported programs (ITS/497/18FP and
GHP/021/18SZ), the Guangdong-Hong Kong-Macao joint
laboratory of optoelectronic and magnetic 6bal materials (no.
2019B121205002), an ECS grant (CityU 21301319), a
Collaborative Research Fund grant (C5037-18G) from the
Research Grants Council of Hong Kong, the Natural Science
Foundation of Guangdong Province (2019A1515010761), the
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