High-Performance Inverted Perovskite Solar Cells Using Doped Poly

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High-Performance Inverted Perovskite Solar Cells Using Doped Poly(triarylamine) as the Hole Transport Layer Yawen Liu, Zhihai Liu, and Eun-Cheol Lee ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b02047 • Publication Date (Web): 22 Feb 2019 Downloaded from http://pubs.acs.org on February 22, 2019

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is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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ACS Applied Energy Materials

High-Performance

Inverted

Perovskite

Solar

Cells

Using

Doped

Poly(triarylamine) as the Hole Transport Layer Yawen Liu,† Zhihai Liu*, ‡§ and Eun-Cheol Lee*, † †Department

of Nano-Physics, Gachon University, Gyeonggi 13120, Republic of

Korea ‡School

of Opto-Electronic Information Science and Technology, Yantai University,

Shandong 264005, China §Department

of Bio-Nano Technology, Gachon University, Gyeonggi 13120,

Republic of Korea KEYWORDS: perovskite solar cells, doping, stability, hole transport layer, CuSCN, CuI, PTAA ABSTRACT Organolead trihalide perovskite materials have attracted considerable interest because of their successful application in fabricating high-efficiency photovoltaic cells. Charge transport layers play a significant role in improving the efficiency and stability of perovskite solar cells (PSCs). In this work, we investigated the p-type doping effect of poly(triarylamine) (PTAA) layer on the performance of PSCs by using three dopants. We observe that doping copper (I) thiocyanate (CuSCN) into PTAA led to a higher performance improvement for the PSCs than the use of copper (I) iodide (CuI) or lithium salt (Li-TFSI) as the dopant. The power conversion efficiency (PCE) of the PSCs significantly improved from 14.22% to 18.16% upon doping 2.0 wt% CuSCN with simultaneously enhanced open-circuit voltage, short-circuit current density, and fill factor. The long-term stability of the PSCs was also improved with significantly reduced PCE degradation (from 79% to 25%) after 200 h. Our results provide a simple method to improve the performance of planar PSCs by adding dopants into PTAA.

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INTRODUCTION In recent times, organometallic trihalide perovskite solar cells (PSCs) have been attracting significant interest because of their unique properties for photovoltaic applications, such as strong absorption in the visible spectrum,1 long and balanced carrier diffusion length,2-6 and solution processability.7 Since first reported by Kojima and coworkers in 2009, the performance of PSCs has improved very rapidly, with a significant increase in power conversion efficiency (PCE) from 3.8% to 23.3% within only a few years, demonstrating immense potential for their commercialization.8-10 Nowadays, inverted planar-structured PSCs have been intensively investigated because of their simple processability at low temperatures.11 Consequently, inverted planar PSCs are believed to be more suitable for large-scale commercialization than mesoporous TiO2-based conventional PSCs.12 For perovskite absorbers, mixed-cationbased perovskites (CsxFAyMA1-x-yPbIzBr3-z, in which MA = methylammonium and FA = formamidinium) have become very popular owing to their better solar property and stability compared with single cation perovskites (MAPbX3 or FAPbX3, X = Cl, Br, or I).13 To further increase the PCE of planar PSCs, numerous endeavors have been directed toward the development of charge transport materials.14-18 Appropriate electron and hole selective contacts should be optimized to minimize the charge carrier recombination and consequent losses in the solar performance of PSCs.19 Although the viability of using an organic electron selective contact [e.g., (6,6)-phenyl C61-butyric acid methyl ester (PCBM)]20,

21

has been recently demonstrated, high-performance

PSCs are based on metal oxides such as ZnO,22 SnO2,23 and TiO2,24-27 or hybrid derivative nanocomposites.28 In contrast, many new hole transport materials (HTMs) have been synthesized and applied in conventional PSCs, in which HTMs are spun directly on top of the perovskite films.14,

15, 17

However, most of these HTMs are

difficult to use in inverted PSCs with the hole transport layer (HTL) underneath the perovskite layer. This is because the general solvents used for perovskite preparation, such as N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), have good 2


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solubility and can wash off most of the commonly used small molecular HTMs, such as

2,2’,7,7’-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9’-spirobifluorene

(spiro-

OMeTAD).29 Therefore, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is the most widely used HTM for inverted PSCs so far.30-32 However, the open-circuit voltage (Voc) (0.90–0.99 V) of the related PSCs is much lower than that (~1.05 V) obtained from meso-super-structured PSCs, which is a major obstacle for the further improvement of the performance of PSCs.33-35 Although the origin of such limited Voc for inverted PSCs is not obvious, it might arise from the mismatched energy levels between the valence band (VB) of perovskite (-5.4 eV) and the work function of PEDOT:PSS (-5.0 eV).36 Recently, other polymer HTMs have been actively investigated in inverted PSCs because of their sustainability in DMF and/or DMSO wash. For instance, using poly [N, N’-bis(4-butylphenyl)-N, N’-bis (phenyl)benzidine] (poly-TPD) or poly(triarylamine) (PTAA) in inverted PSCs significantly increased Voc to approximately 1.10 V because their deeper highest occupied molecular orbital (HOMO) levels.37-39 However, owing to the relatively lower fill factor (FF), the PCEs of these polymer-HTM-based devices are still approximately 15%, which are similar to those of PSCs that use PEDOT:PSS as the HTL.37,

38

To further improve the

performance of PSCs using polymer-based HTMs, the technique of doping some molecules into HTMs has proven to be very effective, with PCE improved to 10.4– 18.2%.39-45 For example, PTAA doped with lithium bis(triﬂuoromethanesulfonyl)imide (Li-TFSI) and 4-tert-butyl pyridine (t-BP) demonstrated enhanced conductivity and/or hole mobility.44 Particularly, Huang and co-workers doped PTAA using 2,3,5,6tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) and achieved a three-fold reduction of the series resistance of the PSCs, which further increased the FF to 74% and Voc to 1.09 V without sacrificing the short-circuit current density (Jsc) of PSCs.39 These studies showed the advantages of the doping effect of the HTMs on the performance of PSCs and provided a direction for further increasing the PCE of PSCs by exploring better dopants.39 However, Li-TFSI, F4-TCNQ and tris[2-(1H-pyrazol-1yl)-4-tert-butylpyridine)cobalt(III)tris(bis(trifluoromethylsulfonyl)imide)] (FK209) are 3



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organic material (F4-TCNQ) and metal-complexes (Li-TFSI and FK209), which may suffer from the disadvantages of the multi-step synthetic route, complex purification process, and poor stability.39, 44, 45 Thus, further efforts are needed to find effective and stable dopants for HTMs. Recently, some p-type inorganic semiconductors have been reported to act as the HTMs in PSCs with better chemical stability and higher hole mobility than organic PEDOT:PSS or PTAA.16, 18, 46-52 Among them, copper salts such as CuSCN and CuI have already been demonstrated to be good HTMs not only for dyesensitized solar cells but also for PSCs owing to their advantages of high conductivity, solution processability, and good stability.18, 51 However, the PCEs of the PSCs that use CuI and CuSCN as HTLs are still lower than those of the PSCs that use PTAA or spiroOMeTAD.18,53-55 For example, Christians and co-workers demonstrated that the PCE of CuI-based PSC is only 6.0%, which is lower than that (7.9%) of the PSC that uses spiro-OMeTAD.18 Arora and co-workers showed that the PCE of the PSCs was slightly decreased from 20.8% to 20.4% by replacing spiro-OMeTAD with CuSCN.46 This might be caused by the formation of VB trap states in these materials, which increase the charge recombination and decrease the Voc of the PSCs.18, 54 CuSCN and CuI have proven to be good dopants for spiro-OMeTAD, which can effectively improve the performance of standard structured PSCs.56 So far, there has been no investigation on doping CuSCN and CuI into a PTAA layer for the fabrication of inverted PSCs. In this work, we improved the performance of inverted PSCs by doping Li-TFSI, CuI, or CuSCN into the HTL of PTAA. We observed that the use of these dopants could enhance the hole conductivity of PTAA layers, which resulted in significant improvements of the PCEs. When using CuSCN-doped PTAA, a significant PCE improvement (from 14.22% to 18.16%) of the PSCs was obtained, which was higher than that of the PSCs that use Li-TFSI (15.19%) or CuI (15.07%). The long-term stability of the PSCs after 200 h was also significantly enhanced; the PCE degradation significantly decreased from 79% to 25%, which was also lower than those of the devices based on Li-TFSI (59%) or CuI (34%). Moreover, the CuSCN-doped PSCs 4


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showed a stable power output and negligible hysteresis. Our results indicate that doping PTAA with CuSCN is a simple and effective way to realize high-performance inverted PSCs. RESULTS AND DISCUSSION

Figure 1. (a) Schematic structure of the PSCs, where the HTL represents PEDOT:PSS, pristine PTAA, or doped PTAA. (b) Energy levels of the pristine PTAA and doped PTAA layers. Those of perovskite and FTO were drawn for comparison. High (c) and low (d) binding energy regions of the UPS spectra for pristine and doped PTAA layers. The device structure of the PSCs is shown in Figure 1a, with fabrication details summarized in Supporting Information. The energy level alignment of FTO, PTAA (pristine and doped), and perovskite layers is shown in Figure 1b, in which the HOMO and LUMO (lowest unoccupied molecular orbital) levels of PTAA layers were determined using UPS; the HOMO edges are determined from linear extrapolations to the background (Figure 1d) using the following equation:57 EHOMO = hʋ − (Ecutoff − Eonset)

(3)

where hʋ is the He I radiation photon energy (21.22 eV), Eonset is the onset of the HOMO level, and Ecutoff is the high-binding-energy cut off. The bandgap (Eg) of the PTAA films 5



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can be determined from the UV–Vis absorption spectra (Figure S4a) using the following equation:58 (αhʋ) 2 = k (hʋ – Eg)

(2)

where k is a constant, hʋ is the photon energy, and α is the absorption coefficient. The LUMO levels of the PTAA films can be calculated using the following equation:59 ELUMO = EHOMO − Eg

(3)

As expected, the Fermi levels (EF) of PTAA films doped with Li-TFSI, CuI, and CuSCN are 0.60, 0.57, and 0.49 eV above their HOMO levels, respectively. These values are less than that (0.65 eV) of the undoped PTAA film, indicating the effective p-doping effect of PTAA layers.60 The HOMO level of the CuSCN-doped PTAA layer is determined to be -5.17 eV, which is also closer to that of the perovskite film than that of pristine PTAA. This might be due to the original lower HOMO level of CuSCN.61 The Li-TFSI- and CuI-doped PTAA layers showed very similar HOMO levels (-5.11 and -5.12 eV, respectively) as the undoped PTAA film. From the UPS results, we conclude that the CuSCN-doped PTAA layer has a more p-type nature and more suitable energy level alignment, which plays a very important role in charge extraction from perovskite absorber.60, 62 We note that LUMO levels obtained from this method may not be very accurate. Some other measurements, such as inverse photoemission spectroscopy, need to be characterized.59 We also measured the FT-IR spectra of the pristine and doped PTAA films (Figure S1). The peak at 1490 cm−1 corresponds to the CC/CN stretching and CH bending vibration, which are associated with the terminal and bridging phenyl groups.63 The bands marked at approximately 1595 and 816 cm−1 are assigned to the CC stretching vibration corresponding to the terminal phenyl groups (t-phenyl) and aromatic CH bending, respectively. Considering the structure of PTAA, the peaks between 1250 and 1320 cm−1 mainly involve aromatic CN stretch vibrations.63 By doping Li-TFSI, CuI, 6


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and CuSCN, these characteristic peaks of PTAA became weaker, which might be caused by the charge transfer from PTAA to dopants.64 The charge distribution and vibrational characteristics of PTAA would be changed if the electrons in the HOMO of PTAA transfer to the acceptor molecules.64 Thus, the reduced intensity of the FT-IR peaks could be explained by the p-doping effect of using these dopants. The cross-sectional SEM image of the PSCs and the AFM images of PTAA films are shown in Figure S2 and S3 with a detailed description summarized in the supporting information. From the UV–vis absorption spectra in Figure S4a, we observed that the transmission of the doped PTAA films was slightly decreased; for example, it decreased by about 0.8% at 450 nm, and its effect on the PCE might be negligible. To understand the doping effect on the PTAA layer, the I–V characteristics were measured in the sandwich-structured devices, which were composed of FTO/PTAA (pristine and doped) (10 nm)/Ag (100 nm) (Figure S4b).65 The DC (direct current) conductivity (σ0) can be determined from the slope of the I–V plots, using the equation:66 I = σ0Ad-1V

(1)

where A is the area of the sample (0.1 cm2) and d is the thickness of the PTAA layers (10 nm).67 The conductivity of the pristine PTAA layer was only 2.74 × 10-4 mS cm1,

whereas the Li-TFSI- and CuI-doped PTAA layers showed improved conductivity of

6.56 × 10-4 and 5.24 × 10-4 mS cm-1, respectively. The CuSCN-doped PTAA film presented a three-fold higher conductivity (8.32 × 10-4 mS cm-1) than pristine PTAA, which might be induced by the high conductivity of CuSCN.47,68 Consequently, it is expected that the photogenerated charge carriers from the perovskite absorber could be more efficiently extracted by the CuSCN-doped PTAA, which will be discussed later.69

7



(b) 1.0

21 18

0.8

15 0.6

6 3 0 0.0

PEDOT:PSS Pristine PTAA Li-TFSI-doped PTAA CuI-doped PTAA CuSCN-doped PTAA 0.2

0.4

0.6

0.8

400

500

600

700

800

Wavelength (nm)

(d)

24 20 20

-2

15 10

0 0.0

0.0 300

1.0

20

5

Pristine PTAA Li-TFSI-doped PTAA CuI-doped PTAA CuSCN-doped PTAA

0.2

Voltage (V)

(c)

0.4

Forward Scan Reverse Scan 0.2

0.4

0.6

0.8

1.0

16

16

12

12

8

8

4

4

0

40

80

Voltage (V)

120

160

PCE (%)

9

IPCE

12

Current Density (mA cm )

Current Density (mA cm-2)

(a)

Current Density (mA cm-2)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0 200

Time (s)

Figure 2. (a) J–V characteristics of the PSCs based on pristine and doped PTAA as HTLs. (b) The corresponding IPCE spectra of PSCs based on pristine and doped PTAA as HTLs. Forward and reverse J–V characteristics (c) and steady maximum power output results (d) of the best PSC based on PTAA doped with CuSCN, measured at a bias voltage of 0.92 V. To optimize the doping concentration, we fixed the doping amount of Li-TFSI according to previous work.53 In the case of copper salts, we varied the doping amount from 2.0 to 3.2 wt.% and 1.6 to 2.8 wt.% for CuI and CuSCN, respectively. As shown in Table S2 and S3, the optimal doping ratios for CuI and CuSCN are 2.8 and 2.0 wt.%, respectively, which lead to the highest PCE for each group. From Figure 2a and Table 1, the PSCs that use PEDOT:PSS present a best PCE of 13.21% with a low Voc of 0.98 V. When changing PEDOT:PSS into PTAA (pristine), the Voc of the PSCs significantly increased to 1.06 V, resulting in a higher PCE of 14.22%. For comparison, the PSCs using pristine CuSCN as HTL exhibited a PCE of 14.92% (Figure S5).

8


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For PSCs based on Li-TFSI-doped PTAA as the HTL, the PCE of the PSCs increased to 15.19%, which is similar to that (15.07%) of the PSCs that use CuI-doped PTAA. In contrast, CuSCN (2.0 wt.%)-doped PSCs show an evidently improved PCE of 18.16% with the lowest series resistance (Rs1). As shown in the histogram (Figure S7), the CuSCN-doped PSCs are observed to have high PCE and good reproducibility by testing a group of 12 individual devices. The statistical results such as average values and standard deviations are shown in Figure S8. The improvement in the average PCE (from 13.70% to 17.90%) is higher than that (from 14.82% to 18.02%) of the PSCs that use spiro-OMeTAD with CuSCN doping.49 Noticeably, the PSCs based on CuSCNdoped PTAA exhibited a Voc of 1.12 V, which is much higher than that of the PSCs in other groups. The improved PCE in CuSCN-doped PSCs also originated from the enhancement of Jsc (from 20.75 to 21.92 mA cm-2) and FF (from 0.64 to 0.75). The improved Voc can be explained by the deeper HOMO level (-5.17 eV) of CuSCN-doped PTAA, which reduced the mismatched energy levels with the VB of perovskite (-5.4 eV). The improved Jsc and FF might be induced by the improved perovskite quality and charge transfer at the interface, which will be discussed later. We note that the PCE values highly depend on the experimental conditions and operation skills in different labs. Our PCEs are similar to those of the PSCs based on PEDOT:PSS or PTAA in previous studies,35-39 indicating that the devices were well optimized in our experiments. Figure 2b presents the incident IPCE spectra of the related PSCs based on pristine and doped PTAA layers. The Jsc values integrated from the IPCE spectra are 20.33, 20.92, 20.81, and 21.45 mA cm-2 for PSCs that use pristine, Li-TFSI-, CuI-, and CuSCN-doped PTAA, respectively. These calculated Jsc values were only 1–2.2% lower than those (20.74, 21.23, 21.02, and 21.92 mA cm-2, respectively) measured from the J–V characteristics in Figure 2a, indicating the high accuracy of our measurements. The enhanced IPCE at a long wavelength range (650–750 nm) maybe caused by the improved light absorption and charge dissociate,70 which will be discussed later. The reference and the optimized PSC (using pristine and 2.0 wt.% CuSCN-doped PTAA) 9



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both showed a negligible photocurrent hysteresis (Figure 2c and Figure S6), indicating that the PSCs have a few defects.55 Ultimately, the steady-state results of the CuSCNdoped PSC are shown in Figure 2d, which indicate a stable Jsc of 19.51 mA cm-2 and a stable PCE of 17.95% for 200 s. Table 1. Summary of the photovoltaic parameters for the PSCs that use PEDOT:PSS, pristine PTAA, Li-TFSI-doped PTAA, CuI-doped PTAA, and CuSCN-doped PTAA as the HTLs. HTL

PEDOT:PSS Pristine PTAA Li-TFSIdoped PTAA CuI-doped PTAA CuSCNdoped

Average/ch ampion

Voc (V)

-2

Jsc (mA cm )

FF

PCE (%)

Average 0.97 ± 0.03 20.65 ± 0.89 0.62 ± 0.06 12.53 ± 0.55 Champion

0.98

20.75

0.65

13.21


1.06

20.74

0.64

14.22


1.07

21.23

0.67

15.19


1.09

21.02

0.65

15.07


1.12

21.92

0.75

18.16

Rs1 (ohm) 137.46 ± 3.21 133.96 185.77 ± 3.63 181.49 175.74 ± 2.38 170.69 179.35 ± 2.75 176.62 108.21 ± 1.12 104.46

PTAA

10


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Figure 3. AFM height and phase images of the perovskite films on different PTAA layers: (a)(e) pristine, (b)(f) Li-TFSI-doped, (c)(g) CuI-doped, and (d)(h) CuSCNdoped cases. (a)-(d) and (e)-(h) are the height and phase images, respectively. To identify the reasons for the performance improvement of PSCs using doped PTAA as HTL, SEM, AFM, UV–vis absorption, and XRD measurements were used to characterize the quality of the upper perovskite films. Figure 3 shows the AFM height (a-d) and phase images (e-h) of the perovskite films on PTAA layers without and with doping. From Figure 3a, the perovskite film fabricated on pristine PTAA layer shows a rough surface morphology with the RMS roughness of 21.0 nm. When Li-TFSI and CuI were doped into the PTAA layer, the roughness of the perovskite films was negligibly changed (21.2 and 22.2 nm, respectively, see Figure 3b and c). In contrast, when CuSCN was doped into PTAA, the perovskite film showed a smoother surface morphology with a smaller RMS roughness of 15.9 nm, which might be induced by the increased perovskite grain size. From Figures 3e-h, it is evident that the grain size of the perovskite becomes larger when Li-TFSI and CuI are doped into a PTAA layer (from approximately 400 to 600 nm). The perovskite on CuSCN-doped PTAA shows an even larger grain size (approximately 850 nm), indicating the improved crystallization upon using the doping technique. This result was also supported by the SEM images in Figure S9, which show a similar trend as the AFM images. The UV– vis absorption spectra and XRD patterns of the perovskite films are shown in Figure 4a and b, which confirm the positive effect of the additives doped in the PTAA on the crystallization of perovskite films. As shown in Figure 4a, the light absorption at the 11



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wavelength range of 450–850 nm gradually improved as the dopants into the PTAA layers were changed from Li-TFSI through CuI to CuSCN, which might be induced by the reduced number of defects and narrowed bandgap of perovskite.11 The improved light absorption is in good agreement with the enhanced IPCE at a long wavelength range (650–750 nm) in Figure 2b. From Figure 4b, the intensities of the (110) and (220) peaks at 14.1° and 28.4° for the perovskite films based on the PTAA with Li-TFS and CuI doping were stronger than those of the perovskite film prepared on pristine PTAA film. Further, the intensities of the (110) and (220) peaks reached the maximum when CuSCN was doped into PTAA, indicating the improved crystallinity of the perovskite films.71 The contact angle measurements (Figure S10) indicate a more hydrophobic property of the doped PTAA layers, which might be caused by the larger grains containing dopants and PTAA. The use of a hydrophobic underlayer is known to be beneficial for perovskite crystallization because of the suppressed heterogeneous nucleation of perovskite, which improved the grain boundary expansion rate of the perovskite.57 As a result, the improved conductivity of the CuSCN-doped PTAA layer, high quality of perovskite, and enhanced charge extraction property in the PSCs would all contribute to low Rs1, resulting in the excellent FF (0.75) upon doping CuSCN in PTAA.39

Figure 4. UV–vis absorption spectra (a) and XRD patterns (b) of the perovskite films on pristine and doped PTAA layers.

12


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Figure 5. Nyquist plots of the PSCs that use pristine and doped PTAA as the HTL under illumination of one sun with a bias of 1 V. To gain further insight into the doping effect of PTAA films on the performance improvement of PSCs, we performed the EIS measurements of the PSCs under illumination of one sun, as shown in Figure 5. From Figure S11, the equivalent circuit consists of the series resistance (Rs2), overall charge transfer resistance (Rct), and chemical capacitance (Cct) of the films, where Rct is related to the resistance and interfacial resistances of the perovskite film.72, 73 From the terminal of semi-circles in Figure 5 and Table S1, the Rct value gradually decreased from 276 to 160 Ω as the dopants into PTAA layer were changed from Li-TFSI through CuI to CuSCN, indicating the improved charge transfer property of the PSCs. The use of CuSCN led to the smallest Rct, which could be attributed to the improved perovskite quality on the CuSCN-doped PTAA layer and improved energy alignment. These are very important factors for improving the charge transfer with less resistance in the PSCs.74, 75 We also estimated the trap density and hole carrier mobility (µhole) of Cs0.05FA0.81MA0.14PbI2.55Br0.45 perovskite based on pristine and doped PTAA by employing the SCLC technique.76, 77 Typically, we fabricated hole-only SCLC devices 13



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with a structure of FTO/PTAA (pristine and doped)/perovskite/PTAA/Au and measured the dark current of these devices under different bias voltages. The thicknesses of PTAA and perovskite films are 10 and 400 nm, respectively. The Figure 6 shows the J–V characteristics of these hole-only devices, indicating three regions of the behavior. The first region at low bias ( 175 μm in Solution-Grown CH3NH3PbI3 Single Crystals. Science 2015, 347, 967-970. (4) Xing, G.; Mathews, N.; Sun, S.; Lim, S. S.; Lam, Y. M.; Grätzel, M.; Mhaisalkar, S.; Sum, T. C., Long-Range Balanced Electron- and Hole-Transport Lengths in Organic-Inorganic CH3NH3PbI3. Science 2013, 342, 344-347. (5) Shi, D.; Adinolfi, V.; Comin, R.; Yuan, M.; Alarousu, E.; Buin, A.; Chen, Y.; Hoogland, S.; Rothenberger, A.; Katsiev, K.; Losovyj, Y.; Zhang, X.; Dowben, P. A.; Mohammed, O. F.; Sargent, E. H.; Bakr, O. M., Low Trap-state Density and Long Carrier Diffusion in Organolead Trihalide Perovskite Single Crystals. Science 2015, 347, 519-522. (6) Chen,

L.;

Xie,

X.;

Liu,

Z.;

Lee,

E.-C.,

A

Transparent

Poly(3,4-

ethylenedioxylenethiophene):Poly(Styrene Sulfonate) Cathode for Low Temperature Processed, Metal-Oxide Free perovskite solar cells. J. Mater. Chem. A 2017, 5, 69746980. (7) Yin, W. J.; Shi, T.; Yan, Y., Unique Properties of Halide Perovskites as Possible Origins of the Superior Solar Cell Performance. Adv. Mater. 2014, 26, 4653-4658. (8) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T., Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chemi. Soc. 2009, 131, 6050-6051. (9) Jung, H. S.; Park, N. G., Perovskite Solar Cells: From Materials to Devices. Small 2015, 11, 10-25. 20


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(10)https://www.nrel.gov/pv/assets/pdfs/pv-efficiencies-07-17-2018 (11)Liu, Y.; Liu, Z.; Lee, E.-C., Dimethyl-Sulfoxide-Assisted Improvement in the Crystallization of Lead-Acetate-Based Perovskites for High-Performance Solar Cells. J. Mater. Chem. C 2018, 6, 6705-6713. (12)Hu, X.; Huang, Z.; Zhou, X.; Li, P.; Wang, Y.; Huang, Z.; Su, M.; Ren, W.; Li, F.; Li, M.; Chen, Y.; Song, Y., Wearable Large-Scale Perovskite Solar-Power Source via Nanocellular Scaffold. Adv. Mater. 2017, 29, 1703236. (13)Saliba, M.; Matsui, T.; Seo, J.-Y.; Domanski, K.; Correa-Baena, J.-P.; Nazeeruddin, M. K.; Zakeeruddin, S. M.; Tress, W.; Abate, A.; Hagfeldt, A.; Grätzel, M., CesiumContaining Triple Cation Perovskite Solar Cells: Improved Stability, Reproducibility and high efficiency. Energy Environ. Sci. 2016, 9, 1989-1997.. (14)Jeon, N. J.; Lee, J.; Noh, J. H.; Nazeeruddin, M. K.; Grätzel, M.; Seok, S. I., Efficient Inorganic–Organic Hybrid Perovskite Solar Cells Based on Pyrene Arylamine Derivatives as Hole-Transporting Materials. J. Am. Chem. Soc. 2013, 135, 1908719090. (15)Qin, P.; Paek, S.; Dar, M. I.; Pellet, N.; Ko, J.; Grätzel, M.; Nazeeruddin, M. K., Perovskite Solar Cells with 12.8% Efficiency by Using Conjugated Quinolizino Acridine Based Hole Transporting Material. J. Am. Chem. Soc. 2014, 136, 8516-8519. (16)Kim, J. H.; Liang, P. W.; Williams, S. T.; Cho, N.; Chueh, C. C.; Glaz, M. S.; Ginger, D. S.; Jen, A. K. Y., High‐Performance and Environmentally Stable Planar Heterojunction Perovskite Solar Cells Based on a Solution ‐ Processed Copper ‐ Doped Nickel Oxide Hole‐Transporting Layer. Adv. Mater. 2015, 27, 695-701. (17)Liu, J.; Wu, Y.; Qin, C.; Yang, X.; Yasuda, T.; Islam, A.; Zhang, K.; Peng, W.; Chen, W.; Han, L., A Dopant-Free Hole-Transporting Material for Efficient and Stable Perovskite Solar Cells. Energy Environ. Sci. 2014, 7, 2963-2967. (18)Christians, J. A.; Fung, R. C. M.; Kamat, P. V., An Inorganic Hole Conductor for Organo-Lead Halide Perovskite Solar Cells. Improved Hole Conductivity with Copper Iodide. J. Am. Chem. Soc. 2014, 136, 758-764. (19)Juarez-Perez, E. J.; Wuβler, M.; Fabregat-Santiago, F.; Lakus-Wollny, K.; Mankel, 21



Page 22 of 38

E.; Mayer, T.; Jaegermann, W.; Mora-Sero, I., Role of the Selective Contacts in the Performance of Lead Halide Perovskite Solar Cells. J. Phys. Chem. Lett. 2014, 5, 680685. (20)Malinkiewicz, O.; Yella, A.; Lee, Y. H.; Espallargas, G. M.; Graetzel, M.; Nazeeruddin, M. K.; Bolink, H. J., Perovskite Solar Cells Employing Organic ChargeTransport Layers. Nat. Photonics 2013, 8, 128. (21)Sun, S.; Salim, T.; Mathews, N.; Duchamp, M.; Boothroyd, C.; Xing, G.; Sum, T. C.; Lam, Y. M., The Origin of High Efficiency in Low-Temperature SolutionProcessable Bilayer Organometal Halide Hybrid Solar Cells. Energy Environ. Sci. 2014, 7, 399-407. (22)Liu, D.; Kelly, T. L., Perovskite Solar Cells with a Planar Heterojunction Structure Prepared Using Room-Temperature Solution Processing Techniques. Nat. Photonics 2013, 8, 133 (23)Jiang, Q.; Chu, Z.; Wang, P.; Yang, X.; Liu, H.; Wang, Y.; Yin, Z.; Wu, J.; Zhang, X.; You, J., Planar-Structure Perovskite Solar Cells with Efficiency beyond 21%. Adv. Mater. 2017, 29, 1703852. (24)Burschka, J.; Pellet, N.; Moon, S.-J.; Humphry-Baker, R.; Gao, P.; Nazeeruddin, M. K.; Grätzel, M., Sequential Deposition as a Route to High-Performance PerovskiteSensitized Solar Cells. Nature 2013, 499, 316. (25)Xiao, Y.; Cheng, N.; Kondamareddy, K. K.; Wang, C.; Liu, P.; Guo, S.; Zhao, X.Z., W-doped TiO2 mesoporous electron transport layer for efficient hole transport material free perovskite solar cells employing carbon counter electrodes. J. Power Sources 2017, 342, 489-494. (26)Liu, M.; Johnston, M. B.; Snaith, H. J., Efficient Planar Heterojunction Perovskite Solar Cells by Vapour Deposition. Nature 2013, 501, 395. (27)Xiao, Y.; Wang, C.; Kondamareddy, K. K.; Cheng, N.; Liu, P.; Qiu, Y.; Qi, F.; Kong, S.; Liu, W.; Zhao, X.-Z., Efficient Electron Transport Scaffold Made up of Submicron TiO2 Spheres for High-Performance Hole-Transport Material Free Perovskite Solar Cells. ACS Appl. Energy Mater. 2018, 1, 5453-5462. 22


Page 23 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(28)Wang, J. T.-W.; Ball, J. M.; Barea, E. M.; Abate, A.; Alexander-Webber, J. A.; Huang, J.; Saliba, M.; Mora-Sero, I.; Bisquert, J.; Snaith, H. J.; Nicholas, R. J., LowTemperature Processed Electron Collection Layers of Graphene/TiO2 Nanocomposites in Thin Film Perovskite Solar Cells. Nano Lett. 2014, 14, 724-730. (29)Yong, Z.; Seul-Gi, K.; Do-Kyoung, L.; Nam-Gyu, P., CH3NH3PbI3 and HC(NH2)2PbI3 Powders Synthesized from Low-Grade PbI2: Single Precursor for HighEfficiency Perovskite Solar Cells. ChemSusChem 2018, 11, 1813-1823. (30)Wang, Q.; Shao, Y.; Dong, Q.; Xiao, Z.; Yuan, Y.; Huang, J., Large Fill-Factor Bilayer Iodine Perovskite Solar Cells Fabricated by a Low-Temperature SolutionProcess. Energy Environ. Sci. 2014, 7, 2359-2365. (31)Xiao, Z.; Bi, C.; Shao, Y.; Dong, Q.; Wang, Q.; Yuan, Y.; Wang, C.; Gao, Y.; Huang, J., Efficient, High Yield Perovskite Photovoltaic Devices Grown by Interdiffusion of Solution-Processed Precursor Stacking Layers. Energy Environ. Sci. 2014, 7, 2619-2623. (32)Nie, W.; Tsai, H.; Asadpour, R.; Blancon, J.-C.; Neukirch, A. J.; Gupta, G.; Crochet, J. J.; Chhowalla, M.; Tretiak, S.; Alam, M. A.; Wang, H.-L.; Mohite, A. D., High-Efficiency Solution-Processed Perovskite Solar Cells with Millimeter-Scale Grains. Science 2015, 347, 522-525. (33)Xiao, Z.; Dong, Q.; Bi, C.; Shao, Y.; Yuan, Y.; Huang, J., Solvent Annealing of Perovskite-Induced Crystal Growth for Photovoltaic‐Device Efficiency Enhancement. Adv. Mater. 2014, 26, 6503-6509. (34)Seo, J.; Park, S.; Chan Kim, Y.; Jeon, N. J.; Noh, J. H.; Yoon, S. C.; Seok, S. I., Benefits of Very Thin PCBM and LiF Layers for Solution-Processed p-i-n Perovskite Solar Cells. Energy Environ. Sci. 2014, 7, 2642-2646. (35)Jung, J. W.; Williams, S. T.; Jen, A. K. Y., Low-Temperature Processed TighPerformance Flexible Perovskite Solar Cells via Rationally Optimized Solvent Washing Treatments. RSC Adv. 2014, 4, 62971-62977. (36)Jung, J. W.; Chueh, C.-C.; Jen, A. K.-Y., High-Performance Semitransparent Perovskite Solar Cells with 10% Power Conversion Efficiency and 25% Average 23



Page 24 of 38

Visible Transmittance Based on Transparent CuSCN as the Hole-Transporting Material. Adv. Energy Mater. 2015, 5, 1500486. (37)Zhao, D.; Sexton, M.; Park, H. Y.; Baure, G.; Nino, J. C.; So, F., High-Efficiency Solution ‐ Processed Planar Perovskite Solar Cells with a Polymer Hole Transport Layer. Adv. Energy Mater. 2015, 5, 1401855. (38)Malinkiewicz, O.; Roldán‐Carmona, C.; Soriano, A.; Bandiello, E.; Camacho, L.; Nazeeruddin, M. K.; Bolink, H. J., Metal ‐ Oxide ‐ Free Methylammonium Lead Iodide Perovskite ‐ Based Solar Cells: the Influence of Organic Charge Transport Layers. Adv. Energy Mater. 2014, 4, 1400345. (39)Wang, Q.; Bi, C.; Huang, J., Doped Hole Transport Layer for Efficiency Enhancement in Planar Heterojunction Organolead Trihalide Perovskite Solar Cells. Nano Energy 2015, 15, 275-280. (40)Zhu, J.-Y.; Niu, K.; Li, M.; Lin, M.-Q.; Li, J.-H.; Wang, Z.-K., PEDOT:PSS-CrO3 composite hole-transporting layer for high-performance p-i-n structure perovskite solar cells. Org. Electron. 2018, 54, 9-13. (41)Wang, Z.-K.; Liao, L.-S., Doped Charge-Transporting Layers in Planar Perovskite Solar Cells. Adv. Opt. Mater. 2018, 6, 1800276. (42)Wang, J.-M.; Wang, Z.-K.; Li, M.; Zhang, C.-C.; Jiang, L.-L.; Hu, K.-H.; Ye, Q.Q.; Liao, L.-S., Doped Copper Phthalocyanine via an Aqueous Solution Process for Normal and Inverted Perovskite Solar Cells. Adv. Energy Mater. 2018, 8, 1701688. (43)Wang, Z.-K.; Li, M.; Yuan, D.-X.; Shi, X.-B.; Ma, H.; Liao, L.-S., Improved Hole Interfacial Layer for Planar Perovskite Solar Cells with Efficiency Exceeding 15%. ACS Appl. Mater. Inter. 2015, 7, 9645-9651. (44)Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Seok, S. I., Solvent engineering for high-performance inorganic–organic hybrid perovskite solar cells. Nat. Mater. 2014, 13, 897. (45)Noh, J. H.; Jeon, N. J.; Choi, Y. C.; Nazeeruddin, M. K.; Grätzel, M.; Seok, S. I., Nanostructured TiO2/CH3NH3PbI3 heterojunction solar cells employing spiroOMeTAD/Co-complex as hole-transporting material. J. Mater. Chem. A 2013, 1, 24


Page 25 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


11842-11847. (46)Jeng, J. Y.; Chen, K. C.; Chiang, T. Y.; Lin, P. Y.; Tsai, T. D.; Chang, Y. C.; Guo, T. F.; Chen, P.; Wen, T. C.; Hsu, Y. J., Nickel Oxide Electrode Interlayer in CH3NH3PbI3 Perovskite/PCBM Planar ‐ Heterojunction Hybrid Solar Cells. Adv. Mater. 2014, 26, 4107-4113. (47)Zhu, Z.; Bai, Y.; Zhang, T.; Liu, Z.; Long, X.; Wei, Z.; Wang, Z.; Zhang, L.; Wang, J.; Yan, F.; Yang, S., High ‐ Performance Hole ‐ Extraction Layer of Sol–Gel ‐ Processed NiO Nanocrystals for Inverted Planar Perovskite Solar Cells. Angew. Chem. Int. Ed. 2014, 53, 12571-12575. (48)You, J.; Meng, L.; Song, T.-B.; Guo, T.-F.; Yang, Y.; Chang, W.-H.; Hong, Z.; Chen, H.; Zhou, H.; Chen, Q.; Liu, Y.; De Marco, N.; Yang, Y., Improved Air Stability of Perovskite Solar Cells via Solution-Processed Metal Oxide Transport Layers. Nat. Nanotechnol. 2015, 11, 75. (49)Chavhan, S.; Miguel, O.; Grande, H.-J.; Gonzalez-Pedro, V.; Sanchez, R. S.; Barea, E. M.; Mora-Sero, I.; Tena-Zaera, R., Organo-Metal Halide Perovskite-Based Solar Cells with CuSCN as the Inorganic Hole Selective Contact. J.Mater. Chem. A 2014, 2, 12754-12760. (50)Ito, S.; Tanaka, S.; Nishino, H., Lead-Halide Perovskite Solar Cells by CH3NH3I Dripping on PbI2–CH3NH3I–DMSO Precursor Layer for Planar and Porous Structures Using CuSCN Hole-Transporting Material. J.Phys. Chem. Lett. 2015, 6, 881-886. (51)Qin, P.; Tanaka, S.; Ito, S.; Tetreault, N.; Manabe, K.; Nishino, H.; Nazeeruddin, M. K.; Grätzel, M., Inorganic Hole Conductor-Based Lead Halide Perovskite Solar Cells with 12.4% Conversion Efficiency. Nat. Commun. 2014, 5, 3834. (52)Sepalage, G. A.; Meyer, S.; Pascoe, A.; Scully, A. D.; Huang, F.; Bach, U.; Cheng, Y. B.; Spiccia, L., Copper(I) Iodide as Hole‐Conductor in Planar Perovskite Solar Cells: Probing the Origin of J–V Hysteresis. Adv. Funct. Mater. 2015, 25, 5650-5661. (53)Yang, W. S.; Park, B.-W.; Jung, E. H.; Jeon, N. J.; Kim, Y. C.; Lee, D. U.; Shin, S. S.; Seo, J.; Kim, E. K.; Noh, J. H.; Seok, S. I., Iodide management in formamidiniumlead-halide–based perovskite layers for efficient solar cells. Science 2017, 356, 137625



Page 26 of 38

1379. (54)Arora, N.; Dar, M. I.; Hinderhofer, A.; Pellet, N.; Schreiber, F.; Zakeeruddin, S. M.; Grätzel, M., Perovskite Solar Cells with CuSCN Hole Extraction Layers Yield Stabilized Efficiencies Greater than 20%. Science 2017 358, 768–771. (55)Luo, D.; Zhao, L.; Wu, J.; Hu, Q.; Zhang, Y.; Xu, Z.; Liu, Y.; Liu, T.; Chen, K.; Yang, W.; Zhang, W.; Zhu, R.; Gong, Q., Dual-Source Precursor Approach for Highly Efficient Inverted Planar Heterojunction Perovskite Solar Cells. Adv. Mater. 2017, 29, 1604758. (56)Li, M.; Wang, Z.-K.; Yang, Y.-G.; Hu, Y.; Feng, S.-L.; Wang, J.-M.; Gao, X.-Y.; Liao, L.-S., Copper Salts Doped Spiro-OMeTAD for High-Performance Perovskite Solar Cells. Adv. Energy Mater. 2016, 6, 1601156.. (57)Kang, S. J.; Yi, Y. J.; Kim, C. Y.; Whang, C. N., Electronic structure of pentacene on hafnium studied by ultraviolet photoelectron spectroscopy. J. Korean Phys. Soc. 2005, 46, L760-L762. (58)Zhang, Y.; Kim, S.-G.; Lee, D.; Shin, H.; Park, N.-G., Bifacial stamping for high efficiency perovskite solar cells. Energy Environ. Sci. 2019, 12, 308-321. (59)Ishii, H.; Sugiyama, K.; Ito, E.; Seki, K., Energy Level Alignment and Interfacial Electronic Structures at Organic/Metal and Organic/Organic Interfaces. Adv. Mater. 1999, 11, 605-625. (60)Endres, J.; Kulbak, M.; Zhao, L.; Rand, B. P.; Cahen, D.; Hodes, G.; Kahn, A.,Electronic Structure of the CsPbBr3/Polytriarylamine (PTAA) System. J. Appl. Phys. 2017, 121, 035304. (61)Gao, P.; Grätzel, M.; Nazeeruddin, M. K., Organohalide Lead Perovskites for Photovoltaic Applications. Energy Environ. Sci. 2014, 7, 2448-2463. (62)Liu, J.; Gao, C.; Luo, L.; Ye, Q.; He, X.; Ouyang, L.; Guo, X.; Zhuang, D.; Liao, C.; Mei, J.; Lau, W., Low-Temperature, Solution Processed Metal Sulfide as an Electron Transport Layer for Efficient Planar Perovskite Solar Cells. J. Mater. Chem. A 2015, 3, 11750-11755. (63)Coates, J., Interpretation of Infrared Spectra, A Practical Approach. Encyclopedia 26


Page 27 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of Analytical Chemistry. (64) Zhang, L.; Zu, F.-S.; Deng, Y.-L.; Igbari, F.; Wang, Z.-K.; Liao, L.-S., Origin of Enhanced Hole Injection in Organic Light-Emitting Diodes with an Electron-Acceptor Doping Layer: p-Type Doping or Interfacial Diffusion? ACS Appl. Mater. Inter. 2015, 7, 11965-11971. (65)Lou, Y.-H.; Xu, M.-F.; Zhang, L.; Wang, Z.-K.; Naka, S.; Okada, H.; Liao, L.-S., Origin of enhanced electrical and conducting properties in pentacene films doped by molybdenum trioxide. Org. Electron. 2013, 14, 2698-2704. (66)Obrzut, J.; Page, K. A., Electrical Conductivity and Relaxation in Poly(3hexylthiophene). Phys. Rev. B 2009, 80, 195211. (67)Chen, B.-X.; Rao, H.-S.; Li, W.-G.; Xu, Y.-F.; Chen, H.-Y.; Kuang, D.-B.; Su, C.Y., Achieving High-Performance Planar Perovskite Solar Cell with Nb-doped TiO2 Compact Layer by Enhanced Electron Injection and Efficient Charge Extraction. J. Mater. Chem. A 2016, 4, 5647-5653. (68)Premalal, E. V. A.; Kumara, G. R. R. A.; Rajapakse, R. M. G.; Shimomura, M.; Murakami, K.; Konno, A., Tuning Chemistry of CuSCN to Enhance the Performance of TiO2/N719/CuSCN All-Solid-State Dye-Sensitized Solar Cell. Chem.Commun. 2010, 46, 3360-3362.. (69)Kakavelakis, G.; Alexaki, K.; Stratakis, E.; Kymakis, E., Efficiency and Stability Enhancement of Inverted Perovskite Solar Cells via the Addition of Metal Nanoparticles in the Hole Transport Layer. RSC Adv. 2017, 7, 12998-13002. (70)Ahn, N.; Kang, S. M.; Lee, J.-W.; Choi, M.; Park, N.-G., Thermodynamic regulation of CH3NH3PbI3 crystal growth and its effect on photovoltaic performance of perovskite solar cells. J. Mater. Chem. A 2015, 3, 19901-19906. (71)Bi, D.; Yi, C.; Luo, J.; Décoppet, J.-D.; Zhang, F.; Zakeeruddin, Shaik M.; Li, X.; Hagfeldt, A.; Grätzel, M., Polymer-Templated Nucleation and Crystal Growth of Perovskite Films for Solar Cells with Efficiency Greater than 21%. Nat. Energy 2016, 1, 16142. (72)Xie, X.; Liu, G.; Xu, C.; Li, S.; Liu, Z.; Lee, E.-C., Tuning the Work Function of 27



Page 28 of 38

Indium-Tin-Oxide Electrodes for Low-Temperature-Processed, Titanium-Oxide-Free Perovskite Solar Cells. Org. Electron. 2017, 44, 120-125. (73)Wei, H.; Xiao, J.; Yang, Y.; Lv, S.; Shi, J.; Xu, X.; Dong, J.; Luo, Y.; Li, D.; Meng, Q., Free-Standing Flexible Carbon Electrode for Highly Efficient Hole-Conductor-Free Perovskite Solar Cells. Carbon 2015, 93, 861-868. (74)Sidhik, S.; Cerdan Pasarán, A.; Esparza, D.; López Luke, T.; Carriles, R.; De la Rosa, E., Improving the Optoelectronic Properties of Mesoporous TiO2 by Cobalt Doping for High-Performance Hysteresis-free Perovskite Solar Cells. CS Appl. Mater. Inter. 2018, 10, 3571-3580. (75)Liu, C.; Huang, Z.; Hu, X.; Meng, X.; Huang, L.; Xiong, J.; Tan, L.; Chen, Y., Grain Boundary Modification via F4TCNQ To Reduce Defects of Perovskite Solar Cells with Excellent Device Performance. ACS Appl. Mater. Inter. 2018, 10, 19091916.. (76)Rose, A., Space-Charge-Limited Currents in Solids. Phys. Rev. 1955, 97, 15381544. (77)Smith, R. W.; Rose, A., Space-Charge-Limited Currents in Single Crystals of Cadmium Sulfide. Phys. Rev. 1955, 97, 1531-1537. (78)Li, M.; Li, B.; Cao, G.; Tian, J., Monolithic MAPbI3 Films for High-Efficiency Solar Cells via Coordination and a Heat Assisted Process. J. Mater. Chem. A 2017, 5, 21313-21319. (79)Gao, L.; Zeng, K.; Guo, J.; Ge, C.; Du, J.; Zhao, Y.; Chen, C.; Deng, H.; He, Y.; Song, H.; Niu, G.; Tang, J., Passivated Single-Crystalline CH3NH3PbI3 Nanowire Photodetector with High Detectivity and Polarization Sensitivity. Nano Lett. 2016, 16, 7446-7454. (80)Jung, J. W.; Chueh, C. C.; Jen, A. K. Y., High ‐ Performance Semitransparent Perovskite Solar Cells with 10% Power Conversion Efficiency and 25% Average Visible Transmittance Based on Transparent CuSCN as the Hole ‐ Transporting Material. Adv. Energy Mater. 2015, 5, 1500486. (81)Ye, S.; Sun, W.; Li, Y.; Yan, W.; Peng, H.; Bian, Z.; Liu, Z.; Huang, C., CuSCN28


Page 29 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Based Inverted Planar Perovskite Solar Cell with an Average PCE of 15.6%. Nano Lett. 2015, 15, 3723-3728. (82)Kawano, K.; Adachi, C., Evaluating Carrier Accumulation in Degraded Bulk Heterojunction Organic Solar Cells by a Thermally Stimulated Current Technique. Adv. Funct. Mater. 2009, 19, 3934-3940. (83)Liu, C.; Li, W.; Li, H.; Zhang, C.; Fan, J.; Mai, Y., C60 Additive-Assisted Crystallization in CH3NH3Pb0.75Sn0.25I3 Perovskite Solar Cells with High Stability and Efficiency. Nanoscale 2017, 9, 13967-13975. (84)Tvingstedt, K.; Malinkiewicz, O.; Baumann, A.; Deibel, C.; Snaith, H. J.; Dyakonov, V.; Bolink, H. J., Radiative Efficiency of Lead Iodide Based Perovskite Solar Cells. Sci. Rep. 2014, 4, 6071. (85)Yin, X.; Chen, P.; Que, M.; Xing, Y.; Que, W.; Niu, C.; Shao, J., Highly Efficient Flexible Perovskite Solar Cells Using Solution-Derived NiOx Hole Contacts. ACS Nano 2016, 10, 3630-3636. (86)Huang, Z.; Hu, X.; Liu, C.; Tan, L.; Chen, Y., Nucleation and Crystallization Control via Polyurethane to Enhance the Bendability of Perovskite Solar Cells with Excellent Device Performance. Adv. Funct. Mater. 2017, 27, 1703061..

29



TOC graphic 60x44mm (300 x 300 DPI)


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Figure 1. (a) Schematic structure of the PSCs, where the HTL represents PEDOT:PSS, pristine PTAA, or doped PTAA. (b) Energy levels of the pristine PTAA and doped PTAA layers. Those of perovskite and FTO were drawn for comparison. High (c) and low (d) binding energy regions of the UPS spectra for pristine and doped PTAA layers. 161x113mm (300 x 300 DPI)



Figure 2. (a) J–V characteristics of the PSCs based on pristine and doped PTAA as HTLs. (b) The corresponding IPCE spectra of PSCs based on pristine and doped PTAA as HTLs. Forward and reverse J–V characteristics (c) and steady maximum power output results (d) of the best PSC based on PTAA doped with CuSCN, measured at a bias voltage of 0.92 V. 161x115mm (300 x 300 DPI)


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Figure 3. AFM height and phase images of the perovskite films on different PTAA layers: (a)(e) pristine, (b)(f) Li-TFSI-doped, (c)(g) CuI-doped, and (d)(h) CuSCN-doped cases. (a)-(d) and (e)-(h) are the height and phase images, respectively. 161x69mm (300 x 300 DPI)



Figure 4. UV–vis absorption spectra (a) and XRD patterns (b) of the perovskite films on pristine and doped PTAA layers。 81x34mm (300 x 300 DPI)


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Figure 5. Nyquist plots of the PSCs that use pristine and doped PTAA as the HTL under illumination of one sun with a bias of 1 V. 81x63mm (300 x 300 DPI)



Figure 6. J–V characteristics of hole-only devices with a structure of FTO/PTAA/perovskite/PTAA/Au using (a) pristine, (b) Li-TFSI-doped, (c) CuI-doped, and (d) CuSCN-doped PTAA. 81x66mm (300 x 300 DPI)


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Figure 7. Normalized Jsc (a), Voc (b), FF (c), and PCE (d) of the PSCs based on pristine and doped PTAA for 200 h. 81x63mm (300 x 300 DPI)



Figure 8. PL (a) and TRPL (b) spectra of perovskite films on pristine and CuSCN-doped PTAA layers. 161x67mm (300 x 300 DPI)


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High-Performance Inverted Perovskite Solar Cells Using Doped Poly

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