Branched Methoxydiphenylamine-Substituted Carbazole Derivatives for Efficient Perovskite Solar Cells: Bigger Is Not Always Better

Povilas Luizys, Jianxing Xia, Maryte Daskeviciene, Kristina Kantminiene, Ernestas Kasparavicius,

Article

Branched Methoxydiphenylamine-Substituted Carbazole

Derivatives for Eﬃcient Perovskite Solar Cells: Bigger Is Not Always

Better

Hiroyuki Kanda, Yi Zhang, Vygintas Jankauskas, Kasparas Rakstys, Vytautas Getautis,*

and Mohammad Khaja Nazeeruddin*

Cite This: https://doi.org/10.1021/acs.chemmater.1c02114

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sı Supporting Information

ABSTRACT: A set of novel branched molecules bearing a diﬀerent

number of 3,6-bis(4,4′-dimethoxydiphenylamino)carbazole-based (Cz-

OMeDPA) periphery arms linked together by aliphatic chains have been

developed, and their performance has been tested in perovskite solar cells

(

PSCs). Electrical and photovoltaic properties have been evaluated with

respect to the number of Cz-OMeDPA moieties and the nature of the

linking aliphatic chain. The isolated compounds possess suﬃcient thermal

stability and are amorphous having high glass-transition temperatures

(

>120 °C) minimizing the risk of direct layer crystallization. The highest

−

5 2

−1 −1

hole-drift mobility of μ = 3.1 × 10 cm V

is comparable to that of

−

−1 −1

the reference standard spiro-OMeTAD (4.1 × 10 cm V s ) under

identical conditions. Finally, PSCs employing two new HTMs (2Cz-

OMeDPA and 3Cz-OMeDPA-OH) bearing two and three substituted

carbazole chromophores, linked by an aliphatic chain, show a performance of around 20%, which is on par with devices using spiro-

OMeTAD and demonstrates slightly enhanced device stability.

INTRODUCTION

and simple functionalization of the structure with a variety of

■

diﬀerent groups, which enable ﬁne-tuning of the optical and

Over the recent years, organic−inorganic hybrid perovskite

solar cells (PSCs) have been receiving marked worldwide

attention owing to their low cost and facile fabrication. Since

009, when Miyasaka and coworkers reported a 3.8% power

conversion eﬃciency (PCE) of PSCs, the performance of

these photovoltaic devices has increased dramatically and

currently, PCE exceeds 25%.

A typical conventional PSC consists of a lead-halide

perovskite layer sandwiched by an electron-selective layer

and an organic hole-selective material, which is an important

counterpart to produce high eﬃciency due to eﬀective hole

extraction/collection and electron blocking from the perovskite

17,18

electronic properties of target HTMs.

Therefore, carba-

zole-based derivatives have been employed in organic light-

19,20

21−23

emitting diodes

and dye-sensitized solar cells.

recent years, carbazole has also attracted much attention in

24−29

PSCs.

In this context, the 3,6-bis(4,4′-dimethoxydiphenylamino)-

carbazole moiety, whose facile synthesis requires just a few

steps from commercially available and cheap starting reagents,

30−32

has been widely explored.

The majority of these studies

consistently demonstrate that the number of carbazole-based

periphery arms in N-aryl substituted carbazole molecules is of

crucial importance for solar cell PCE. For example, hole

mobility and conductivity of X51 are higher than those of X19,

leading to better photovoltaic performance of the investigated

to the metal anode.

The well-known spirobiﬂuorene

derivative 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-

,9′-spirobiﬂuorene (spiro-OMeTAD) is the most widely

devices (Figure 1a). The results are congruous with the

used hole-transporting material (HTM) in PSCs. As spiro-

OMeTAD is relatively expensive, the synthesis of novel low-

Received: June 18, 2021

Revised: August 11, 2021

cost and highly eﬃcient HTMs is still a determinant challenge

for future large-scale PSC production. Recently, HTMs

representing various classes of organic compounds have been

−16

synthesized, as reviewed in numerous review articles.

The low-cost 9H-carbazole as a starting material is

interesting due to its excellent charge-transport properties

XXXX The Authors. Published by

American Chemical Society

Chem. Mater. XXXX, XXX, XXX−XXX

nonconjugated carbazole derivatives.

Article

Figure 1. Chemical structures of the reported HTMs containing Cz-OMeDPA arms: (a) N-aryl substituted carbazole molecules and (b) partially

Figure 2. Chemical structures of the N-alkyl substituted carbazole HTMs containing OMeDPA arms reported herein.

expected inﬂuence of the larger conjugated system in the HTM

X51. However, the PCE of PSCs, in which the tetraphenyl-

ethylene-based structure with four carbazole-based periphery

arms (dly-1) is employed as HTM, is lower than that of the

devices with the semiconductor bearing two carbazole-based

periphery arms as HTM (dly-2). In their study of N-aryl

Chem. Mater. XXXX, XXX, XXX−XXX

Chemistry of Materials

Article

Scheme 1. Divergent Synthesis Route to Cz-OMeDPA, 2Cz-OMeDPA, and 3Cz-OMeDPA

substituted carbazole derivatives, Wu and coworkers have

demonstrated that the number of carbazole-based periphery

arms signiﬁcantly inﬂuences the physical properties of HTM

and its application in PSCs. HTM bearing four arms (W4) has

been shown to perform very well in PSCs, whereas HTM

bearing just two arms (W3) was not even tested due to

OMeDPA) periphery arms linked together by aliphatic chains

(Figure 2) and investigation of their structure−property

relationship. The photoelectrical and photovoltaic properties

of the novel compounds in PSCs have been investigated with

respect to the number of Cz-OMeDPA moieties and the nature

of the linking aliphatic chain.

insuﬃcient solubility (Figure 1a). Interestingly, a twin

molecule, V886, bearing a partially nonconjugated 1,2-

bismethylbenzene core has demonstrated almost state-of-the-

RESULTS AND DISCUSSION

■

Synthesis. The target compounds bearing one (Cz-

OMeDPA), two (2Cz-OMeDPA), or three (3Cz-OMeDPA)

substituted carbazole chromophores linked by an aliphatic

chain were synthesized according to a divergent synthesis

pathway as depicted in Scheme 1. The alkylation reaction of

3,6-dibromocarbazole (1) with 1-bromopropane in THF in the

presence of anhydrous Na SO and KOH at a reﬂux

art performance. In the consistent study of this type of

compound, we have demonstrated that performance of such

twin molecules can be improved by modifying carbazole-based

periphery arms in the central benzene core. However, an

increased number of branches in V1039 and V957 did not

improve the performance (Figure 1b).

To the best of our knowledge, 3,6-bis(4,4′-

dimethoxydiphenylamino)carbazole derivatives bearing photo-

conductive chromophores linked by aliphatic chains have not

been employed in PSCs as HTMs. However, Benhattab et al.

synthesized carbazole-based twin molecules linked by non-

conjugated linear alkyl chains of diﬀerent lengths and

investigated the properties of these twin molecules in the

solid-state DSSCs for the ﬁrst time. They have demonstrated

that conjugated linkers are not essential for designing twin

temperature of the reaction mixture aﬀorded 3,6-dibromo-9-

propyl-9H-carbazole (2). The Buchwald−Hartwig cross-

coupling reaction of intermediate 2 with bis(4-

methoxyphenyl)amine provided the model compound Cz-

OMeDPA with an extended π-electron conjugated system.

With the aim of increasing the number of π-electron

conjugated system by increasing the number of chromophores

in the molecule, the target compound 2Cz-OMeDPA

containing two linked carbazolyl moieties was synthesized.

The reaction of 3,6-dibromo-9-epoxypropylcarbazole (3) with

molecules.

Alkyl chains are attracting attention as they usually improve

solubility and, therefore, enhance the pore ﬁlling of the

perovskite layer by HTM forming a strong and close

attachment to the perovskite to enhance charge transfer. The

HTM therefore is needed to have a low tendency to crystallize,

easily forming a smooth layer at the interface to favor the

charge transfer. In a majority of cases, the alkyl chains are the

ones to signiﬁcantly inﬂuence the stability of the amorphous

state, which is of crucial importance in the formation of good-

3,6-dibromocarbazole in the presence of anhydrous Na SO

2 4

and KOH aﬀorded 1,3-bis(3,6-dibromo-9H-carbazol-9-yl)-2-

propanol (4). However, the attempts to carry out the

Buchwald−Hartwig reaction of 4 with bis(4-methoxyphenyl)-

amine failed. It has been assumed that the hydroxyl group in

the molecule passivates the catalyst. Therefore, the hydroxyl

group was replaced by the propoxy group during the alkylation

reaction of 4 with 1-bromopropane to give 1,3-bis(3,6-

dibromo-9H-carbazol-9-yl)-2-propoxypropane (5). The Buch-

wald−Hartwig reaction of intermediate 5 with bis(4-

methoxyphenyl)amine aﬀorded the target twin molecule

2Cz-OMeDPA.

quality layers.

Considering the above-mentioned information, we report

the synthesis of branched molecules bearing a diﬀerent number

of 3,6-bis(4,4′-dimethoxydiphenylamino)carbazole-based (Cz-

Chem. Mater. XXXX, XXX, XXX−XXX

Chemistry of Materials

Article

Scheme 2. Convergent Synthesis Route to 2Cz-OMeDPA-OH, 3Cz-OMeDPA-OH, 4Cz-OMeDPA, and 4Cz-OMeDPA-OH

As the next step toward an increased number of photo-

conductive moieties, the derivative 3Cz-OMeDPA bearing

three carbazolyl chromophore molecules was synthesized.

First, dimer 4 was transformed into its glycidyl ether 6 via the

reaction of 4 with epichlorohydrin to aﬀord 1,3-bis(3,6-

dibromo-9H-carbazol-9-yl)-2-(2,3-epoxy)propoxypropane (6).

Then, the nucleophilic oxirane ring opening reaction of 6 with

participating in the reaction to give the unblocked 3,6-bis(4,4′-

dimethoxydiphenylamino)-9H-carbazole (10). Compound 10

was converted into its oxirane derivative 11 in the reaction

with epichlorohydrin. The next synthesis steps provided dimer

2Cz-OMeDPA-OH bearing the OH group in the linking

aliphatic chain and its glycidyl ether 12 according to the

synthesis procedure depicted for compound 6 in Scheme 1.

Afterward, the reaction of glycidyl ether 12 with the precursor

10 aﬀorded trimer 3Cz-OMeDPA-OH bearing the OH group

in the aliphatic linker, which was not synthesized via a

divergent synthesis route (Scheme 1). Treatment of the former

compound with epichlorohydrin provided oxirane derivative

13, which upon subsequent reaction with precursor 10

aﬀorded the target tetramer 4Cz-OMeDPA-OH, in which

four substituted carbazole chromophores are linked by the

aliphatic moiety bearing the OH group. The target compound

4Cz-OMeDPA was synthesized by alkylating the hydroxyl

group in 4Cz-OMeDPA-OH with 1-bromopropane.

All HTMs bearing photoconductive chromophores in their

molecules were puriﬁed by column chromatography followed

by precipitation. Isolated by such a procedure, target products

Cz-OMeDPA, 2Cz-OMeDPA, 2Cz-OMeDPA-OH, 3Cz-

OMeDPA, 3Cz-OMeDPA-OH, 4Cz-OMeDPA, and 4Cz-

OMeDPA-OH are amorphous compounds and all attempts

to crystallize them failed. It can be assumed that the obtained

high morphological stability of the synthesized compounds

may be explained by the ﬂexibility of the branched aliphatic

binding chains between photoconductive chromophores. In

addition, the existence of several diasteroisomers of 3Cz-

OMeDPA, 3Cz-OMeDPA-OH, 4Cz-OMeDPA, and 4Cz-

OMeDPA-OH, which have several chiral carbon atoms, is

,6-dibromocarbazole in THF in the presence of anhydrous

Na SO and KOH provided trimer 7. Since the Buchwald−

Hartwig reaction does not occur in the presence of the

hydroxyl group in the molecule, the alkylation reaction of 7

with 1-bromopropane was carried out to replace the hydroxyl

group with the propoxy one in the intermediate compound,

which was subsequently treated with bis(4-methoxyphenyl)-

amine under the conditions of the Buchwald−Hartwig reaction

to obtain the target compound 3Cz-OMeDPA.

The attempts to synthesize a derivative bearing four

substituted carbazole chromophores linked by an aliphatic

chain via the divergent synthesis pathway did not yield the

target compound. Therefore, this HTM was synthesized by the

convergent synthesis route (Scheme 2). First, the intermediate

compound 9-benzyl-3,6-dibromo-9H-carbazole (8) with the

blocked N−H group was synthesized in the reaction of 3,6-

dibromocarbazole (1) with benzyl bromide at reﬂux temper-

ature of the toluene−water reaction mixture in the presence of

KOH and tetrabutylammonium bromide as interphase catalyst.

Next, the Buchwald−Hartwig reaction of 8 with bis(4-

methoxyphenyl)amine provided 9-benzyl-3,6-bis(4,4′-dime-

thoxydiphenylamino)-9H-carbazole (9), which was dissolved

in dimethyl sulfoxide and treated with a 1 M solution of

potassium tert-butoxide in THF with the atmospheric oxygen

Chem. Mater. XXXX, XXX, XXX−XXX

Article

Figure 3. (a) TGA heating curves of the HTMs (heating rate of 10 °C/min and N atmosphere) and (b) DSC curves of the second run (heating

rate of 10 °C/min and N atmosphere).

Table 1. Thermal, Optical, and Photophysical Properties of the HTMs

μ (cm V s⁻¹

−1

T_g(°C)

T_d_e_c(°C)

λ_a_b_s(nm)

λ_P_L(nm)

Φ_P_L(%)

I_P(eV)

E_g(eV)

E_e_a(eV)

)

Cz-OMeDPA

Cz-OMeDPA-OH

379

398

402

410

400

408

409

305, 372

303, 372

302, 373

303, 372

303, 373

448

449

452

449

450

452

4.99

5.16

5.08

5.17

5.12

5.16

5.18

2.92

2.97

2.92

2.88

2.94

2.91

2.82

2.07

2.19

2.16

2.29

2.18

2.25

2.36

2.2 × 10⁻

3.2 × 10

2.4 × 10⁻

1.2 × 10⁻

3.1 × 10⁻

−

121

126

121

120

131

−

6.9 × 10

4.0 × 10⁻

Glass-transition (T ) and decomposition (T ) temperatures determined from DSC and TGA, respectively (10 °C/min and N atmosphere).

dec

−4

UV−vis and PL spectra were measured in THF solutions (10 M). Ionization energies of the ﬁlms measured using PESA. E estimated from

the intersection of absorption and emission spectra of solid ﬁlms. E = I − E . Mobility value at zero ﬁeld strength.

attributed to the stability of the amorphous state of these

HTMs. The synthesized HTMs containing a diﬀerent number

of Cz-OMeDPA arms have a well-deﬁned structure, and they

show good room-temperature solubility in a variety of organic

solvents, i.e., acetone, toluene, chlorobenzene, MEK, and THF.

presumably, be explained by the higher molecular mass

resulting in stronger intermolecular interactions. The same

pattern has been observed for the compounds bearing the

hydroxyl group in the branched aliphatic chain. Their T_d_e_c

values are slightly higher than those of the respective HTMs

without hydroxyl groups. These results indicate the inﬂuence

of the intermolecular hydrogen bonds.

DSC analysis has shown that all investigated compounds

exist only in an amorphous state since no endothermic melting

peaks were detected during both heating cycles (Figures S1 −

S7). From the data in Figure 3b and Table 1, it can be found

that the molecules bearing a diﬀerent number of Cz-OMeDPA

The structures of the HTMs have been conﬁrmed by H

NMR, C NMR, IR spectroscopy, mass spectrometry, and

elemental analysis.

Thermal Properties. The thermal behavior of the HTMs

was evaluated by thermogravimetric analysis (TGA) and

diﬀerential scanning calorimetry (DSC) measurements. The

data are provided in Figure 3, and the summarized character-

istics are listed in Table 1. As seen from the TGA results, all

compounds are thermally stable up to ∼400 °C, which is

somewhat a lower temperature than that of spiro-OMeTAD

moieties show just insigniﬁcant variations in T , i.e., 121−131

°C. The only notable exception is T of the compound Cz-

OMeDPA bearing just one substituted carbazole chromo-

phore. Its T is much lower (T = 81 °C) than those of the

(

T_d_e_c= 449 °C). The lowest 5% weight loss temperature

(T_d_e_c) of 379 °C has been recorded for Cz-OMeDPA bearing

compounds bearing a greater number of carbazole fragments.

With an increase in the number of substituted carbazole

chromophores, the T_gvalues for 3Cz-OMeDPA, 4Cz-

OMeDPA, and 4Cz-OMeDPA-OH are also increased, leading

to a stabilized amorphous state compared with spiro-

OMeTAD (124 °C). In general, it is advantageous to use

fully amorphous compounds as there is no risk of direct ﬁlm

one substituted carbazole fragment; however, it is still high

enough, indicating suﬃcient thermal stability needed in PSCs.

The highest T_d_e_cof 410 °C has been determined for 4Cz-

OMeDPA bearing four substituted carbazole chromophores

linked by the branched aliphatic chain. Overall, just small

variations in T_d_e_cvalues have been observed in the set of the

synthesized compounds with diﬀerent numbers of Cz-

OMeDPA arms. However, a slight increase in T_d_e_cvalues can

be noticed with the increasing number of photoconductive Cz-

OMeDPA arms in the synthesized HTMs. This tendency can,

crystallization in photovoltaic devices.

Optical Properties. The optical properties were evaluated

by UV−vis absorption and photoluminescence spectroscopy in

dilute THF solutions and thin ﬁlms on a glass substrate. UV−

Chem. Mater. XXXX, XXX, XXX−XXX

Article

Figure 4. UV−vis absorption (solid line) and photoluminescence (dashed line) spectra of the investigated HTMs in THF solution (10⁻⁴M).

vis spectra of the synthesized compounds in solution are

similar, as strong π−π* absorptivity is observed at 270−350

nm, and weaker energy absorption, which can be assigned to

n−π* bands, is present at ∼373 nm (Figure 4). The diﬀerent

number of carbazole fragments in the molecules does not

inﬂuence conjugation; just the hyperchromic eﬀect is noted in

the series starting from Cz-OMeDPA, through 2Cz-OMeDPA

and 3Cz-OMeDPA, to 4Cz-OMeDPA. A similar trend was

observed for the compounds 2Cz-OMeDPA-OH, 3Cz-

OMeDPA-OH, and 4Cz-OMeDPA-OH. Thus, absorptivity

is directly proportional to the number of Cz-OMeDPA

moieties in the synthesized compounds. This relationship has

been deﬁnitely proven once again by the structures of the

synthesized HTM molecules. Changes in the branched

aliphatic chains linking photoconductive chromophores do

not inﬂuence the absorption spectra of the target compounds.

The same pattern applies to the characteristics of the materials

investigated in the thin ﬁlms. Signiﬁcant changes in the UV−

Figure 5. Photoemission in air spectra of HTMs.

vis spectra have not been observed in the case of the ﬁlms on

the glass substrate (Figure S8). All investigated HTMs emitted

light with a maximum at around 450 nm and a photo-

hole transport from the photoactive perovskite to the electrode

should be fulﬁlled.

Furthermore, the charge mobility of the synthesized HTMs

was recorded using the xerographic time of ﬂight (XTOF)

technique for solution-processed ﬁlms (for more details, see

the Methods section) measuring hole-drift mobility on electric

ﬁeld strength dependency. The results obtained are shown in

luminescence quantum yield (Φ ) of ∼20% in THF solutions

estimated using the integrated sphere method. In addition, a

relatively large Stokes shift of ∼80 nm was observed for the

synthesized compounds, which suggests signiﬁcant changes in

the geometry of the photoconductors upon excitation. We next

calculated the optical gaps (E = 2.9 eV) from the intersection

of UV−vis and PL spectra on glass substrates.

Figure 6. As shown in Table 1, in the series of the branched

Photoelectrical Properties. To better understand the

HOMO−LUMO level alignment of the synthesized HTMs in

−5

derivatives, the zero-ﬁeld hole-drift mobility (μ ) of 3.1 × 10

−1 −1

cm V

for 2Cz-OMeDPA-OH is the highest, while that

PSCs, the solid-state ionization potential (I ) of their thin ﬁlms

of the analogue with alkylated hydroxyl group 2Cz-OMeDPA

was recorded by photoelectron emission spectroscopy in air

−6

−1 −1

is an order of magnitude lower (3.2 × 10 cm V s ).

Interestingly, a larger number of photoconductive chromo-

phores have a negative inﬂuence on the hole-drift mobility of

the synthesized HTMs. The hole-drift mobility of 3Cz-

OMeDPA-OH with three Cz-OMeDPA moieties is somewhat

lower than that of 2Cz-OMeDPA-OH, while the value for

HTM with four Cz-OMeDPA moieties (4Cz-OMeDPA-OH)

was even lower at weak electric ﬁelds. The same pattern has

been noticed among the HTMs with alkylated hydroxyl groups

(

PESA), as shown in Figure 5. As it has been expected, among

the molecules bearing the same chromophores linked together

by aliphatic chains, only insigniﬁcant variations were detected,

with the lowest value of 4.99 eV measured for Cz-OMeDPA

and the highest one of 5.18 eV recorded for 4Cz-OMeDPA-

OH. In all cases, the I values are similar to that of spiro-

OMeTAD (5.00 eV), which optimally oﬀsets with the

perovskite valence band energy (∼5.5 eV); therefore, eﬀective

Chem. Mater. XXXX, XXX, XXX−XXX

Article

Figure 6. Electric ﬁeld dependencies of the hole-drift mobility (μ) in charge transport layers of investigated HTMs.

Cz-OMeDPA, 3Cz-OMeDPA, and 4Cz-OMeDPA. It is

nanoparticle layer, which was deposited on FTO glass coated

important to note that the hole-drift mobility value of Cz-

with compact TiO . The device was completed by 70 nm thick

OMeDPA is much lower (2.2 × 10⁻cm V s ), showing

that, in the present case, the nonbranched molecular structure

is disadvantageous for the eﬃcient hole transport.

−1 −1

HTL and 70 nm gold as back contacts.

The current−voltage (J−V) traces of the record devices of

each HTM are provided in Figure 7b, and their PV parameters

are summarized in Table 2; also, the statistics of PCE are

presented in Figure S11. The PCE values of the most eﬃcient

devices containing 2Cz-OMeDPA, 3Cz-OMeDPA-OH, and

spiro-OMeTAD were very similar, i.e., 20.06%, 19.89%, and

The observed drop in charge mobility may be explained by

the less ordered packing of the more branched molecules with

a larger number of side groups since charges are hopping

between molecules spaced further apart. Usually, the mobility

in the molecular solids is calculated according to the

0.25%, respectively. The hysteresis of the devices was

Borsenberger, Pautmeier, and Bassler formula

evaluated based on the J−V curves collected by scanning the

device from forward bias (FB) to the short circuit (SC) named

as F followed by scanning from SC to FB named as R (Figures

7d−f and S9). The data has revealed that the devices based on

new HTMs of 2Cz-OMeDPA and 3Cz-OMeDPA-OH

exhibited similar hysteretic behavior as compared to spiro-

OMeTAD.

l Å

Å i 2σ y Ñ o Åi σ y

Å j

z Ñ o Å

1/2

Å j

z Ñ

Åj

μ(E, T) = μ ′expÅ−

ÑexpmCÅj z − Σ ÑE

}

Å j

z Ñ o Åj

3kT

o Å kT

Å k

ÇÅ

{ Ñ

Åk

{

ÖÑ

ÖÑ n ÇÅ

(

Here, μ is the hole-drift mobility; μ ′ is the mobility

To realize the performance diﬀerence between the HTMs,

time-resolved photoluminescence (TRPL) measurements

prefactor; σ is the energy width of the hopping site manifold,

which is a measure of the energetic disorder; Σ is the degree of

−

(

Figure 7c) based on glass/perovskite/HTMs construction

positional disorder; C is the empirical constant of 2.9 × 10

−

1 0.5

were performed to study the decay to hole injection processes,

as well as the decay time was ﬁtted by the bi-exponential model

(

cm V ) ; E is the electric ﬁeld; and kT has its usual

meaning. As seen from formula 1, the zero-electric ﬁeld

mobility μ(0, T) is determined mainly by the energetic

disorder σ; therefore, we may assume that energetic disorder is

lower in the case of less-branched HTMs bearing two or three

Cz-OMeDPA moieties as compared to the analogous

compounds with four branches having the highest steric

disorder. Finally, the hole mobility of 2Cz-OMeDPA-OH is

equivalent to that of the reference standard spiro-OMeTAD

with the fast (τ ) and slow (τ ) components, which indicated

the interfacial transportation and recombination; the average

∑

^Ai^τ

delay time (τ ) is calculated by τ

, where A and τ

i i

^Ai^τ

ave

represent the decay amplitude and components of delay time,

^r^e^s^p^e^c^tⁱ^v^e^l^y^.^F^o^r^t^h^eⁱⁿ^t^e^r^f^a^cⁱ^a^l^t^r^aⁿ^s^p^o^r^t^a^tⁱ^oⁿ^,^t^h^e^f^a^s^t⁽^τ1⁾

components were considered. As expected, a signiﬁcant

−

−1 −1 38

quenching is visible in the ﬁrst 50 ns for the most eﬃcient

HTMs. The derived time constants of 21.3 and 43.6 ns were

retrieved for 2Cz-OMeDPA and 3Cz-OMeDPA-OH, respec-

tively, and a somewhat faster process with τ = 16.8 ns was

obtained for the spiro-OMeTAD/perovskite interface (Table

S1 ). On the contrary, a long-living component was observed

for the least eﬃcient compounds. These results have indicated

that all of the HTMs can assist the hole transportation and

2Cz-OMeDPA is the best among HTMs for the hole

(

4.1 × 10 cm V s ).

Photovoltaic Properties. The n−i−p PSCs with the

architecture FTO/C-TiO /SnO /PCBM/perovskite/HTM/

Au were fabricated, as shown in Figure 7a (the details are

given in the Methods section). The FAMAPbI dominated the

perovskite composition, and the HTM layers were doped. The

thickness of the corresponding layers was determined by cross-

sectional scanning electron microscopy (SEM). The device

was made by layering 700 nm perovskite atop a thin SnO₂

Chem. Mater. XXXX, XXX, XXX−XXX

Article

Figure 7. (a) Illustration of the devices constructed from FTO/C-TiO /SnO /PCBM/perovskite/HTM/Au, along with the corresponding cross-

sectional SEM image; (b) champion J−V curves of various HTMs based on PSC; (c) TRPL of various HTMs in the construction of glass/

perovskite/HTM; reverse and forward scan of J−V curves based on (d) 2Cz-OMeDPA, (e) 3Cz-OMeDPA-OH, and (f) spiro-OMeTAD; and (g)

stability of devices based on spiro-OMeTAD, 3Cz-OMeDPA-OH, and 2Cz-OMeDPA (the humidity is lower than 10%, N -ﬁlled box).

collection, which is just a little less for the hole transportation

eﬃciency than spiro-OMeTAD. The results may be the reason

for the slightly lower PCE of 2Cz-OMeDPA compared with

that of spiro-OMeTAD.

As shown in Figure 7g, the stability of the unencapsulated

devices containing the best performing HTMs was measured

dimethoxydiphenylamino)carbazole (Cz-OMeDPA) in the

periphery linked by aliphatic chains as hole-transporting

materials for PSCs are reported. The inﬂuence of the diﬀerent

number of Cz-OMeDPA fragments has been revealed through

the optical, electrochemical, photophysical, and photovoltaic

measurements. Notably, the molecular engineering of Cz-

under 1 sun illumination while stored under a N atmosphere.

OMeDPA arms resulted in the charge drift mobility of μ = 3.1

−

−1 −1

Devices containing 2Cz-OMeDPA are the most stable, and

their stability was slightly better than that of the devices

containing 3Cz-OMeDPA-OH and spiro-OMeTAD.

10 cm V s , which is comparable to that of the

−5

−1 −1

reference standard spiro-OMeTAD (4.1 × 10 cm V s )

under identical conditions. Most importantly, PSCs employing

Cz-OMeDPA bearing two carbazole chromophores showed a

CONCLUSIONS

■

performance of over 20%, which is the best result among the

series being on par with spiro-OMeTAD, and demonstrated

the enhanced device stability.

To conclude, the synthesis and a systematic study of the

branched molecules bearing a diﬀerent number of 3,6-bis(4,4′-

Chem. Mater. XXXX, XXX, XXX−XXX

Chemistry of Materials

The Supporting Information is available free of charge at

Article

and then ethanol. The C-TiO layer was prepared by spraying TAA

solution in ethanol (0.2 mL of TAA in 6 mL of anhydrous ethanol) at

Table 2. Photovoltaic Parameters of Reverse (R) and

Forward (F) Scans Obtained from the Champion Devices

Based on Various HTMs

50 °C. SnO nanoparticles were diluted with deionized water in a

ratio of 1:4 and coated on the C-TiO substrate at a speed of 3000

rpm for 20 s with a ramp-up of 2000 rpm s followed by the ﬁnal

HTMs

J_s_c(mA cm⁻²) V_o_c(V) FF (%) PCE (%)

−1

heating at 150 °C for 10 min. A 10 mg/mL concentration solution of

Cz-OMeDPA R

Cz-OMeDPA F

23.62

23.35

24.15

24.16

23.7

23.24

23.59

23.26

24.05

24.07

23.51

23.61

23.36

22.16

24.05

24.22

1.009

0.985

1.071

1.021

1.001

0.971

1.054

1.004

1.054

1.015

1.012

0.988

0.993

0.946

1.079

1.039

74.3

72.6

77.4

76.6

77.2

73.4

75.1

74.2

78.3

75.9

76.3

17.77

16.73

20.06

18.95

18.33

16.60

18.72

17.38

19.89

18.53

18.15

17.78

16.55

14.19

20.25

19.33

PCBM in chlorobenzene was prepared and was spin-coated on the

SnO layer at a speed of 3000 rpm for 20 s with a ramp-up of 2000

Cz-OMeDPA R

Cz-OMeDPA F

Cz-OMeDPA-OH R

Cz-OMeDPA-OH F

Cz-OMeDPA R

−1

rpm s followed by the ﬁnal heating at 100 °C for 10 min. Afterward,

perovskite solutions (the ratio of PbI , MAI, FAI, and PbBr was

:0.16:0.84:0.11, and 1.38 mmol/mL PbI solution and 0.305 mmol/

mL MACl solution were added to the perovskite solution; the solvent

was prepared by mixing DMSO and DMF in a ratio of 1:4) were

successively spin-coated on the substrates at 1000 rpm for 10 s and

Cz-OMeDPA F

000 rpm for 30 s, respectively. Chlorobenzene (200 μL) was added

dropwise for 10 s at 5000 rpm. Perovskite ﬁlms were annealed at 150

C for 10 min. The control HTM solution was prepared by dissolving

5 mg of spiro-OMeTAD (Merck) and additives in 1 mL of

chlorobenzene. For each sample solution of the synthesized HTMs,

0 mg of the compound was dissolved in 1 mL of chlorobenzene. Li-

Cz-OMeDPA-OH R

Cz-OMeDPA-OH F

Cz-OMeDPA-OH R

Cz-OMeDPA-OH F

Cz-OMeDPA R

71.1

67.5

77.9

76.7

Cz-OMeDPA F

bis(triﬂuoromethanesulfonyl)imide (18 μL) from the stock solution

(520 mg in 1 mL of acetonitrile), 13 μL of FK209 [tris (2-(1H-

pyrazol-1-yl)-4-tert-butylpyridine)-cobalt(III) tris(bis

spiro-OMeTAD R

spiro-OMeTAD F

(triﬂuoromethylsulfonyl)imide) (375 mg in 1 mL of acetonitrile)],

and 30 μL of 4-tert-butylpyridine were added as additives. The HTM

layer was formed by spin-coating the solution at 4000 rpm for 20 s. As

the ﬁnal step, the 70 nm thick Au electrode was deposited by thermal

evaporation. All preparative work to deposit PCBM, perovskite, and

HTMs was performed inside the glove box under nitrogen to

minimize the inﬂuence of moisture and oxygen.

METHODS

■

Ionization Potential Measurements. The solid-state ionization

potential (I ) was measured according to the electron photoemission

42−44

in air

by dissolving HTMs in THF and coating layers of 0.5−1

μm thickness on the Al plate, which was precoated with methyl

methacrylate and methacrylic acid copolymer adhesive layers (∼0.5

μm thick). Samples were illuminated with monochromatic light

originating from a quartz monochromator with a deuterium lamp.

Device Characterization. The SEM of the ﬁlm morphology was

investigated by using a high-resolution SEM (Merlin, Zeiss) equipped

with a GEMINI II column and a Schottky Field Emission gun. Images

were acquired with an in-lens secondary electron detector. For the PL

lifetime measurements, samples were excited with a 408 nm pulsed

laser (MDL 300, PicoQuant) with a pulse energy density of 40 μm

−

The power of the incident light beam was 2−5 × 10 W. A negative

voltage of −300 V was supplied to the sample substrate. A counter

electrode with a 4.5 × 15 mm slit for illumination was placed at a

−

cm . Current−voltage characteristics were recorded by applying an

external potential bias to the cell while recording the generated

photocurrent with a digital source meter (Keithley Model 2400). The

light source was a 450 W xenon lamp (Oriel) equipped with a Schott

K113 Tempax sunlight ﬁlter (Praezisions Glas & Optik GmbH) to

match the emission spectrum of the lamp to the AM1.5G standard.

Before each measurement, the exact light intensity was determined

using a calibrated Si reference diode equipped with an infrared cutoﬀ

distance of 8 mm from the sample surface. For the photocurrent

measurement, the counter electrode was connected to the input of the

BK2-16 type electrometer working in the open input regime. The

strength of the photocurrent in the circuit under illumination was

−

−12

−10

A. The photocurrent I depends on the incident light

0.5

photon energy hν. The I = f(hν) dependence was plotted. The

dependence of the photocurrent on incident light quanta energy is

_d_e_s_c_r_i_b_e_d_b_y_a_l_i_n_e_a_r_r_e_l_a_t_i_o_n_s_h_i_p_b_e_t_w_e_e_n_I0.5 and hν near the

ﬁlter (KG-3, Schott). The cells were masked with an active area of

threshold. The linear part of this dependence was extrapolated to the

.09 cm to ﬁx the active area and reduce the inﬂuence of the

hν axis, and the I value was determined as the photon energy at the

scattered light for the small device. All measurements were carried out

at room temperature in air.

interception point.

Hole-Drift Mobility Measurements. Samples were prepared by

spin-coating the HTM solution on the polyester ﬁlm with a

conductive Al layer. The thickness of the spin-coated layer was 5−

ASSOCIATED CONTENT

sı Supporting Information

45,46

■

0 μm. The hole-drift mobility was measured by XTOF.

The

electric ﬁeld was created by positive corona charging. Charge carriers

were generated at the layer surface by illumination with pulses of the

nitrogen laser (pulse duration, 2 ns; wavelength, 337 nm). The layer

surface potential decreased up to 1−5% of initial potential before

illumination as a result of pulse illumination. The capacitance probe

connected to the wide frequency band electrometer measured the

https://pubs.acs.org/doi/10.1021/acs.chemmater.1c02114.

General procedures, synthetic methods, additional

ﬁgures, and tables (DSC, UV-PL, hysteresis, ﬁtting

parameters, etc.) (PDF )

speed of the surface potential decrease dU/dt. The transit time t was

determined by the kink on the curve of the dU/dt transient on a

double logarithmic scale. Drift mobility was calculated according to

AUTHOR INFORMATION

the formula μ = d /U t , where d is the layer thickness and U is the

■

surface potential at the moment of illumination.

Corresponding Authors

Thermal Properties. DSC was performed with a Q10 calorimeter

Vytautas Getautis − Department of Organic Chemistry,

Kaunas University of Technology, Kaunas 50254, Lithuania;

orcid.org/0000-0001-7695-4677;

(

TA Instruments) at a scan rate of 10 K min⁻under a nitrogen

atmosphere. The glass-transition temperature of each synthesized

compound was determined during the second heating scan. TGA was

performed with a Q50 TGA (TA Instruments) at a scan rate of 10 K

Email: vytautas.getautis@ktu.lt

−

Mohammad Khaja Nazeeruddin − Group for Molecular

min under a nitrogen atmosphere.

Device Fabrication. The chemically etched FTO glass (Nippon

Sheet Glass) was cleaned with detergent solution, followed by acetone

Engineering of Functional Material, Institute of Chemical

Sciences and Engineering, Ecole Polytechnique Fédérale de

Chem. Mater. XXXX, XXX, XXX−XXX

Chemistry of Materials

Stable Perovskite Solar Cells Using Low-Cost Aniline-Based Enamine

Article

Lausanne, CH-1951 Sion, Switzerland; orcid.org/0000-

Hole-Transporting Materials. Adv. Mater. 2018 , 30 , 1 −7.

001-5955-4786 ; Email: mdkhaja.nazeeruddin@ep ﬂ .ch

(7) Yu, Z.; Sun, L. Recent Progress on Hole-Transporting Materials

Authors

for Emerging Organometal Halide Perovskite Solar Cells. Adv. Energy

Mater. 2015, 5, 1500213.

Povilas Luizys − Department of Organic Chemistry, Kaunas

(8) Teh, C. H.; Daik, R.; Lim, E. L.; Yap, C. C.; Ibrahim, M. A.;

University of Technology, Kaunas 50254, Lithuania

Jianxing Xia − Group for Molecular Engineering of Functional

Material, Institute of Chemical Sciences and Engineering,

Ludin, N. A.; Sopian, K.; Mat Teridi, M. A. A. Review of Organic

Small Molecule-Based Hole-Transporting Materials for Meso-

Structured Organic −Inorganic Perovskite Solar Cells. J. Mater.

Chem. A 2016, 4, 15788−15822.

Ecole Polytechnique Fédérale de Lausanne, CH-1951 Sion,

Switzerland

(9) Ameen, S.; Rub, M. A.; Kosa, S. A.; Alamry, K. A.; Akhtar, M. S.;

Maryte Daskeviciene − Department of Organic Chemistry,

Kaunas University of Technology, Kaunas 50254, Lithuania

Kristina Kantminiene − Department of Physical and

Inorganic Chemistry, Kaunas University of Technology,

Kaunas 50254, Lithuania

Shin, H. S.; Seo, H. K.; Asiri, A. M.; Nazeeruddin, M. K. Perovskite

Solar Cells: Influence of Hole Transporting Materials on Power

Conversion Efficiency. ChemSusChem 2016, 9, 10−27.

(10) Calió, L.; Kazim, S.; Grätzel, M.; Ahmad, S. Hole-Transport

Materials for Perovskite Solar Cells. Angew. Chem., Int. Ed. 2016, 55,

11) Wang, Y.-K.; Jiang, Z.-Q.; Liao, L.-S. New Advances in Small

4522−14545.

Ernestas Kasparavicius − Department of Organic Chemistry,

Kaunas University of Technology, Kaunas 50254, Lithuania

Hiroyuki Kanda − Group for Molecular Engineering of

Functional Material, Institute of Chemical Sciences and

Molecule Hole-Transporting Materials for Perovskite Solar Cells.

Chin. Chem. Lett. 2016, 27, 1293−1303.

(12) Urieta-Mora, J.; García-Benito, I.; Molina-Ontoria, A.; Martín,

Engineering, Ecole Polytechnique F é d é rale de Lausanne, CH-

N. Hole Transporting Materials for Perovskite Solar Cells: A

951 Sion, Switzerland; orcid.org/0000-0002-0327-

Chemical Approach. Chem. Soc. Rev. 2018 , 47 , 8541 −8571.

775

(13) Zhou, W.; Wen, Z.; Gao, P. Less Is More: Dopant-Free Hole

Yi Zhang − Group for Molecular Engineering of Functional

Transporting Materials for High-Efficiency Perovskite Solar Cells.

Adv. Energy Mater. 2018, 8, 1702512.

Material, Institute of Chemical Sciences and Engineering,

(14) Rakstys, K.; Igci, C.; Nazeeruddin, M. K. Efficiency vs. Stability:

Dopant-Free Hole Transporting Materials towards Stabilized Perov-

skite Solar Cells. Chem. Sci. 2019, 10, 6748 −6769.

Ecole Polytechnique Fédérale de Lausanne, CH-1951 Sion,

Switzerland

Vygintas Jankauskas − Institute of Chemical Physics Vilnius

University, Vilnius 10257, Lithuania

Kasparas Rakstys − Department of Organic Chemistry,

Kaunas University of Technology, Kaunas 50254, Lithuania

(15) Sheibani, E.; Yang, L.; Zhang, J. Recent Advances in Organic

Hole Transporting Materials for Perovskite Solar Cells. Sol. RRL

020, 4, 2000461.

16) Yin, X.; Song, Z.; Li, Z.; Tang, W. Toward Ideal Hole

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.chemmater.1c02114

Transport Materials: A Review on Recent Progress in Dopant-Free

Hole Transport Materials for Fabricating Efficient and Stable

Perovskite Solar Cells. Energy Environ. Sci. 2020, 13, 4057−4086.

(

17) Kato, S.; Noguchi, H.; Kobayashi, A.; Yoshihara, T.; Tobita, S.;

Author Contributions

Nakamura, Y. Bicarbazoles: Systematic Structure −Property Inves-

tigations on a Series of Conjugated Carbazole Dimers. J. Org. Chem

2012, 77, 9120−9133.

(18) Prachumrak, N.; Pojanasopa, S.; Namuangruk, S.; Kaewin, T.;

Jungsuttiwong, S.; Sudyoadsuk, T.; Promarak, V. Novel Bis[5-

P.L. and J.X. contributed equally to this work.

Notes

The authors declare no competing ﬁnancial interest.

Fluoren-2-Yl)Thiophen-2-Yl]Benzothiadiazole End-Capped with

ACKNOWLEDGMENTS

■

Carbazole Dendrons as Highly Efficient Solution-Processed Non-

doped Red Emitters for Organic Light-Emitting Diodes. ACS Appl.

Mater. Interfaces 2013, 5, 8694−8703.

(19) Wex, B.; Kaafarani, B. R. Perspective on Carbazole-Based

Organic Compounds as Emitters and Hosts in TADF Applications. J.

Mater. Chem. C 2017 , 5 , 8622 −8653.

The authors acknowledge the support of the H2020 program

for Solar-ERANET funding of the BOBTANDEM (2019-

022) and the Swiss National Science Foundation. K.R.

acknowledges funding from the Research Council of Lithuania

via Grant no. 09.3.3-LMT-K-712-19-0061 and the funding

received from the MJJ Foundation. Dr. E. Kamarauskas is

acknowledged for ionization potential measurements.

20) Ledwon, P. Recent Advances of Donor-Acceptor Type

Carbazole-Based Molecules for Light Emitting Applications. Org.

Electron. 2019, 75, 105422.

21) Lai, H.; Hong, J.; Liu, P.; Yuan, C.; Li, Y.; Fang, Q. Multi-

REFERENCES

Carbazole Derivatives: New Dyes for Highly Efficient Dye-Sensitized

■

(

1) Rong, Y.; Hu, Y.; Mei, A.; Tan, H.; Saidaminov, M. I.; Il, S. S.;

Solar Cells. RSC Adv. 2012, 2, 2427.

McGehee, M. D.; Sargent, E. H.; Han, H. Challenges for

Commercializing Perovskite Solar Cells. Science 2018, 361,

No. eaat8235.

(22) El-Sherbiny, D.; Cheema, H.; El-Essawy, F.; Abdel-Megied, A.;

El-Shafei, A. Synthesis and Characterization of Novel Carbazole-

Based Terpyridyl Photosensitizers for Dye-Sensitized Solar Cells

(DSSCs). Dyes Pigm. 2015, 115, 81−87.

(23) An, J.; Yang, X.; Cai, B.; Zhang, L.; Yang, K.; Yu, Z.; Wang, X.;

Hagfeldt, A.; Sun, L. Fine-Tuning by Triple Bond of Carbazole

Derivative Dyes to Obtain High Efficiency for Dye-Sensitized Solar

Cells with Copper Electrolyte. ACS Appl. Mater. Interfaces 2020, 12,

46397−46405.

(24) Daskeviciene, M.; Paek, S.; Wang, Z.; Malinauskas, T.;

Jokubauskaite, G.; Rakstys, K.; Cho, K. T.; Magomedov, A.;

Jankauskas, V.; Ahmad, S.; et al. Carbazole-Based Enamine: Low-

Cost and Efficient Hole Transporting Material for Perovskite Solar

Cells. Nano Energy 2017, 32, 551−557.

2) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. Organometal

Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells.

J. Am. Chem. Soc. 2009, 131, 6050−6051.

(

3) Best Research-Cell Eﬃciency Chart | Photovoltaic Research |

NREL. 2021.

4) Green, M. A.; Ho-Baillie, A.; Snaith, H. J. The Emergence of

Perovskite Solar Cells. Nat. Photonics 2014 , 8 , 506 −514.

5) Park, N.-G. Perovskite Solar Cells: An Emerging Photovoltaic

Technology. Mater. Today 2015, 18, 65−72.

6) Vaitukaityte, D.; Wang, Z.; Malinauskas, T.; Magomedov, A.;

Bubniene, G.; Jankauskas, V.; Getautis, V.; Snaith, H. J. Efficient and

Chem. Mater. XXXX, XXX, XXX−XXX

Chemistry of Materials

Article

25) Li, M.; Wang, Z.; Liang, M.; Liu, L.; Wang, X.; Sun, Z.; Xue, S.

(40) Yu, W.; Yang, Q.; Zhang, J.; Tu, D.; Wang, X.; Liu, X.; Li, G.;

Guo, X.; Li, C. Simple Is Best: A p-Phenylene Bridging

Methoxydiphenylamine-Substituted Carbazole Hole Transporter for

High-Performance Perovskite Solar Cells. ACS Appl. Mater. Interfaces

2019, 11, 30065−30071.

Low-Cost Carbazole-Based Hole-Transporting Materials for Perov-

skite Solar Cells: Influence of S,N-Heterocycle. J. Phys. Chem. C 2018,

26) Berton, N.; Nakar, R.; Schmaltz, B. DMPA-Containing

22, 24014−24024.

Carbazole-Based Hole Transporting Materials for Perovskite Solar

(41) De Mello, J. C.; Wittmann, H. F.; Friend, R. H. An Improved

Experimental Determination of External Photoluminescence Quan-

tum Efficiency. Adv. Mater. 1997, 9, 230−232.

Cells: Recent Advances and Perspectives. Synth. Met. 2019, 252, 91−

(

06.

(42) Cardona, M.; Ley, L. Photoemission in Solids I - General

27) Daskeviciene, M.; Paek, S.; Magomedov, A.; Cho, K. T.; Saliba,

Principles , Springer: Berlin, Heidelberg, 1978; Vol. 26. DOI: 10.1007/

-540-08685-4

43) Miyamoto, E.; Yamaguchi, Y.; Yokayama, M. Ionization

M.; Kizeleviciute, A.; Malinauskas, T.; Gruodis, A.; Jankauskas, V.;

Kamarauskas, E.; et al. Molecular Engineering of Enamine-Based

Small Organic Compounds as Hole-Transporting Materials for

Perovskite Solar Cells. J. Mater. Chem. C 2019, 7, 2717−2724.

potential of organic pigment thin film by atmospheric photoelectron

analysis. J. Xerography 1989, 28, 364−370.

(

28) Gao, L.; Schloemer, T. H.; Zhang, F.; Chen, X.; Xiao, C.; Zhu,

(44) Kirkus, M.; Tsai, M. H.; Grazulevicius, J. V.; Wu, C. C.; Chi, L.

K.; Sellinger, A. Carbazole-Based Hole-Transport Materials for High-

Efficiency and Stable Perovskite Solar Cells. ACS Appl. Energy Mater.

C.; Wong, K. T. New Indole-Carbazole Hybrids as Glass-Forming

High-Triplet-Energy Materials. Synth. Met. 2009 , 159 , 729 −734.

(

020, 3, 4492−4498.

(45) Vaezi-Nejad, S. M. Xerographic Time of Flight Experiment for

29) Rakstys, K.; Paek, S.; Drevilkauskaite, A.; Kanda, H.;

the Determination of Drift Mobility in High Resistivity Semi-

Daskeviciute, S.; Shibayama, N.; Daskeviciene, M.; Gruodis, A.;

Kamarauskas, E.; Jankauskas, V.; et al. Carbazole-Terminated

Isomeric Hole-Transporting Materials for Perovskite Solar Cells.

ACS Appl. Mater. Interfaces 2020, 12, 19710−19717.

conductors. Int. J. Electron. 1987 , 62 , 361 −384.

(46) Chan, A. Y. C.; Juhasz, C. Xerographic-Mode Transient Charge

Technique for Probing Drift Mobility in High-Resistivity Materials.

Int. J. Electron. 1987, 62, 625−632.

(

30) Xu, B.; Sheibani, E.; Liu, P.; Zhang, J.; Tian, H.; Vlachopoulos,

N.; Boschloo, G.; Kloo, L.; Hagfeldt, A.; Sun, L. Carbazole-Based

Hole-Transport Materials for Efficient Solid-State Dye-Sensitized

Solar Cells and Perovskite Solar Cells. Adv. Mater. 2014, 26, 6629−

(

634.

31) Li, D.; Shao, J.-Y.; Li, Y.; Li, Y.; Deng, L.-Y.; Zhong, Y.-W.;

Meng, Q. New Hole Transporting Materials for Planar Perovskite

Solar Cells. Chem. Commun. 2018, 54, 1651−1654.

32) Zhu, L.; Shan, Y.; Wang, R.; Liu, D.; Zhong, C.; Song, Q.; Wu,

F. High-Efficiency Perovskite Solar Cells Based on New TPE

Compounds as Hole Transport Materials: The Role of 2,7- and 3,6-

Substituted Carbazole Derivatives. Chem. − Eur. J. 2017, 23, 4373−

(

379.

33) Gratia, P.; Magomedov, A.; Malinauskas, T.; Daskeviciene, M.;

Abate, A.; Ahmad, S.; Grätzel, M.; Getautis, V.; Nazeeruddin, M. K. A

Methoxydiphenylamine-Substituted Carbazole Twin Derivative: An

Efficient Hole-Transporting Material for Perovskite Solar Cells.

Angew. Chem., Int. Ed. 2015, 54, 11409−11413.

(

34) Magomedov, A.; Paek, S.; Gratia, P.; Kasparavicius, E.;

Daskeviciene, M.; Kamarauskas, E.; Gruodis, A.; Jankauskas, V.;

Kantminiene, K.; Cho, K. T.; et al. Diphenylamine-Substituted

Carbazole-Based Hole Transporting Materials for Perovskite Solar

Cells: Influence of Isomeric Derivatives. Adv. Funct. Mater. 2018, 28,

(

704351.

35) Benhattab, S.; Nakar, R.; Rodriguez Acosta, J. W.; Berton, N.;

Faure-Vincent, J.; Bouclé, J.; Tran Van, F.; Schmaltz, B. Carbazole-

Based Twin Molecules as Hole-Transporting Materials in Dye-

Sensitized Solar Cells. Dyes Pigm. 2018, 151, 238−244.

(

36) Tomkute-Luksiene, D.; Daskeviciene, M.; Malinauskas, T.;

Jankauskas, V.; Degutyte, R.; Send, R.; Pschirer, N. G.; Wonneberger,

H.; Bruder, I.; Getautis, V. Molecular Engineering of the Hole-

Transporting Material Spiro-OMeTAD via Manipulation of Alkyl

Groups. RSC Adv. 2016, 6, 60587−60594.

(

37) Tomkute-Luksiene, D.; Malinauskas, T.; Daskeviciene, M.;

Gaidelis, V.; Maldzius, R.; Sidaravicius, J.; Getautis, V. Synthesis of the

Hole-Transporting Molecular Glasses Possessing Pendant 3,6-

Dibromocarbazolyl Moieties. Synth. Met. 2011, 161, 1177−1185.

(

38) Malinauskas, T.; Tomkute-Luksiene, D.; Sens, R.; Daskeviciene,

M.; Send, R.; Wonneberger, H.; Jankauskas, V.; Bruder, I.; Getautis,

V. Enhancing Thermal Stability and Lifetime of Solid-State Dye-

Sensitized Solar Cells via Molecular Engineering of the Hole-

Transporting Material Spiro-OMeTAD. ACS Appl. Mater. Interfaces

015, 7, 11107−11116.

39) Borsenberger, P. M.; Pautmeier, L.; Bässler, H. Charge

Transport in Disordered Molecular Solids. J. Chem. Phys. 1991, 94,

447−5454.