Fulleropyrrolidinium Iodide As an Efficient Electron Transport Layer for

Subscriber access provided by University of Otago Library

Article

Fulleropyrrolidinium Iodide as An Efficient Electron Transport Layer for Air-Stable Planar Perovskite Solar Cells Jiabin Huang, Xuegong Yu, Jiangsheng Xie, Chang-Zhi Li, Yunhai Zhang, Dikai Xu, Zeguo Tang, Can Cui, and Deren Yang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 29 Nov 2016 Downloaded from http://pubs.acs.org on November 29, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces 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.

Page 1 of 21

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

ACS Applied Materials & Interfaces

Fulleropyrrolidinium Iodide as An Efficient Electron Transport Layer for Air-Stable Planar Perovskite Solar Cells Jiabin Huang, † Xuegong Yu, *,† Jiangsheng Xie, † Chang-Zhi Li,*

，‡

Yunhai Zhang, ||

Dikai Xu, † Zeguo Tang,§ Can Cui, || and Deren Yang† †

State Key Laboratory of Silicon Materials and School of Materials Science & Engineering, Zhejiang University, Hangzhou 310027, China ‡ Department of Polymer Science & Engineering, Zhejiang University, Hangzhou 310027, China § Ritsumeikan Global Innovation Research Organization, Ritsumeikan University, Nojihigashi, Kusatsu, Shiga 525-8577, Japan || Center for Optoelectronics Materials and Devices, Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018, China

ABSTRACT Organic-inorganic halide perovskite solar cells have attracted great attention in recent years. But there are still a lot of unresolved issues related to the perovskite solar cells such as the phenomenon of anomalous hysteresis characteristics and long-term stability of the devices. Here, we developed a simple three-layered efficient perovskite device by replacing the commonly employed PCBM electrical transport layer with an ultrathin fulleropyrrolidinium iodide (C60-bis) in an inverted p-i-n architecture. The devices with an ultrathin C60-bis electronic transport layer yield an average power conversion efficiency of 13.5% and a maximum efficiency of 15.15%. Steady state photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements show that the high performance is attributed to the efficient blocking of holes and high extraction efficiency of electrons by C60-bis, due to a favorable energy level alignment between the CH3NH3PbI3 and the Ag electrodes. The hysteresis effect and stability of our perovskite solar cells with C60-bis become better under indoor humidity conditions.

KEYWORDS:

perovskite

solar

cells,

electrical

transport

fulleropyrrolidinium iodide, stability, hysteresis effect, CH3NH3PbI3

1

ACS Paragon Plus Environment

layer,


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

Page 2 of 21

INTRODUCTION Organic-inorganic hybrid perovskite solar cells (PvSCs) have attracted great attention of researchers in the last few years due to their capabilities in achieving high-efficiency through solution-fabrication of low cost materials.1, 2 These materials exhibit excellent optoelectronic properties such as strong optical absorption coefficient,

3-5

long carrier lifetime (~ 1 µ s) 6 and high carrier mobility (~10 cm2 V−1

s−1). 7 The band gap of perovskite can be tailored in the range from the ultraviolet to infrared region through varying components.2,

8-9

Most importantly, the excited

organic-inorganic lead halide perovskite yield the loosely bonded Wannier excitons (bonding energy of ~25 meV)10, which can easily dissociate into free charges on the costs of tiny thermal dynamic driven. Therefore, PvSCs can be made into versatile device architectures including mesoscopic and planar heterojunction structures.

11-12

Typically, organic/inorganic electron and hole transport layers (ETL and HTL), such as

2,2’7,7’-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9’-spirobifluorene

(spiro-OMeTAD),

11, 13

14-15

fullerene (C60),

[6,6]-phenyl C61-butyric acid methyl

ester (PCBM) 16-17 and conjugated polymers 18 as well as metal oxides, are frequently employed to form heterojunction with perovskite layer generating highly efficient photovoltaic

effect.

For

instance,

inverted

p-i-n

planar

device

with

a

HTL-perovskite-ETL architecture can deliver over 18% power conversion efficiencies with relatively small hysteresis. 19-21 However, to access such efficient devices usually involved the complicated fabrication procedures, such as multiple-layer based ETL (PCBM/C60 or PCBM/C60-bis) and HTL, technique,

27

20-26

the complicated doping,

24

hot-casting

and/or high temperature annealing, which would bring issues when

considering the device area scale-up and reproducibility. Especially, the exact function and mechanism for each separated component of multiple-layers in high efficiency perovskite solar cells are worthy to be understood. To this end, the simple PvSCs architecture consisting with all solution-processed three HTL-Perovskite-ETL layers is promising because of their simple fabrication process. The first inverted planar structure of perovskite solar cells got a PCE of 3.9% 2


Page 3 of 21

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


by using the traditional organic transport layers poly(3,4-ethylenedioxythio phene):poly(styrenesulfonicacid) (PEDOT:PSS) and fullerene derivative as the HTL and ETL in a perovskite device. 15 However, researchers are aware of drawbacks from the hydrophobic and acidic PEDOT:PSS, which is the lack of long-term stability.

25

Alternatively, the NiO has recently been proven to be a good HTL for CH3NH3PbI3 perovskite, due to its high optical transparency, chemical stability, good hole conductivity and work function tunabilities from 5.0 to 5.6 eV. The efficient NiO/CH3NH3PbI3/PCBM PHJ hybrid solar cells have demonstrated a PCE of 7.8%. 28 Subsequently, a mesoscopic NiO/CH3NH3PbI3/PCBM junction device demonstrated a PCE of 9.51%.

29

Recently, Han et al. have used heavily doped NiO layers in large

area planar PvSCs to achieve 16.2% efficiency and high stability of a PCE degradation of less than 10% after exposing the cells for 1000 hours at short–circuit condition to full sunlight from a solar simulator. 24 On the other hand, few attentions have been paid on the optimizing the ETL, except for the generally used PCBM ETL. Note that relatively low short circuit current density (Jsc) has been obtained in the structure of NiO/CH3NH3PbI3/PCBM, 24, 28-29

which means PCBM is not an efficient material for extracting electrical carriers.

So previous researches have been used C60 and PCBM in combination with metal oxides or polymers as the ETLs to enhance the electron transfer and improve the Jsc, such as TiO2/fullerene

self-assembled monolayer (C60-SAM),

30

ZnO/PCBM,

31

polyethylenimine (PEI)/PCBM 32 in the regular cell architecture and PCBM/C60-bis 33 in inverted cell architecture. PCBM and C60 alone can also function as ETLs in both regular and inverted cell architectures. 34-35 Herein, we report that efficient and simple three-layered inverted p-i-n PvSCs have been developed for the first time, consisting of a planer heterojunction of perovskite with thin fulleropyrrolidinium iodide (C60-bis) ETL and NiO HTL. C60-bis was not only used to tune the work-function of electrode, but also to enable better energetic alignment between the perovskite and electrode and it also promotes optimal interfacial contact to minimize the potential loss across this corresponding 3



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

interface. 36 As a result, the inverted PvSCs with C60-bis ETL and NiO HTL can yield good performance of 15.15% (with averaged PCE of 13.5%), which 4 times higher than devices without ETL. Also, over 80% of its original efficiency of our perovskite solar cells using the C60-bis ETL can be dramatically preserved after 240 h of exposure in ambient condition (under humidity of ～30%). The detailed device characterization revealed that the improvement of PvSC performance is attributed to the good interfacial properties of fulleropyrrolidinium iodide ETL between the CH3NH3PbI3 and the Ag electrodes.

EXPERIMENTAL DETAILS Material synthesis CH3NH3I was synthesized by the method in our previous work.48 CH3NH3I•PbI2•DMSO adduct was synthesized by 1 mole (461mg) PbI2 (99%, Sigma-Aldrich), 1 mole (159 mg) CH3NH3I and 71 µl dimethyl sulfoxide (DMSO, 99.5%, Sigma-Aldrich) mixed in 625 µl N, N-dimethylformamide (DMF, 99.8%, Sigma-Aldrich).

Thin film and solar cell fabrication We adopted the FTO glasses (Nippon Sheet Glass Co., Japan, 8 ohm−2) with an optical transmission of greater than 80% in the visible range. After thoroughly washing with deionized water, detergent solution, acetone and ethanol for 10 min in ultrasonic cleaner, we prepared to fabricate NiO films. The method for NiO layer deposition was modified slightly from previous report

24

: the cleaned FTO glasses

were placed on a hotplate at the temperature of 500 °C, then 30 ml acetonitrile/ethanol (with 95: 5 volume ratio) solution of nickel acetylacetonate was sprayed within 10 min by an air nozzle onto the hot FTO glasses. After spraying, the film was further treated at 500 °C for another 20 min to promote NiO crystallization. NiO film thickness could be changed by varying the concentration of solution from 0.01M to 0.05M. After cooling, the NiO coated FTO glasses was prepared to deposit 4


Page 4 of 21

Page 5 of 21

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


CH3NH3PbI3 perovskite layer. The method for perovskite layer deposition was modified from previous report 46. Firstly, 461 mg PbI2, 159 mg CH3NH3I, and 71 µL DMSO (molar ratio 1:1:1) were mixed in 625 µL of DMF solution with stirring for 1 h at room temperature in order to prepare a CH3NH3I • PbI2 • DMSO adduct solution. Then, the completely dissolved solution was spin-coated on the NiO layer at 1000 rpm for 5 sec and 5000 rpm for another 20 sec and 600 µL of diethyl ether was drop-casted quickly on the rotating substrate at 20th sec before the surface changed to be turbid by rapid vaporization of DMF. Next, the transparent CH3NH3I • PbI2 • DMSO adduct film was heated at 65 °C for 1 min and 100 °C for 10 min in order to obtain a dense CH3NH3PbI3 film. After cooling, an isopropanol solution of C60-bis was then spin-coated on the perovskite layer at 3000 rpm for 30 sec. Finally, 100 nm thick Ag contacts were deposited under high vacuum (< 1.0×10–3 Pa) by using thermal evaporator at a constant evaporation rate of 0.1 nm/s. Note that the whole process was done in atmosphere.

Film and device characterization Film characterization: we used the UV-vis-NIR spectrophotometer (U-4100, Hitachi, Japan) to measure the Optical absorbance spectra of perovskite films on glass in the wavelength range of 300-850 nm. X-ray diffraction measurement (PANalytical, Utrecht, The Netherlands) was used to determine the crystal structures of the PbI2 and CH3NH3PbI3 formed on the FTO films. A field emission scanning electron microscope (FE-SEM HITACH S4800) and the atomic force microscope (AFM, Dimension Edge, Bruker) were used to observe the morphologies of perovskite films. Fluorescence spectrophotometer (FLS920, Edinburgh Instruments) was used to measure the photoluminescence (PL) spectra and time-resolved PL spectra where the excited wavelength was 635 nm and detected in the wavelength range of 700 to 850nm with 10 nm increment. Device characterization: we used the Keithley 2400 source meter and a solar simulator (94022A, Newport®) to measure the photocurrent density and voltage curves. The light intensity was corrected by using a standard Si solar cell (PVM937, 5



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

Newport®). Our device area was 0.12 cm2 and the measurement process was similar to our previous work.

48

An external quantum efficiency (EQE) measurement system

(QEX10, PV Measurements, Inc.) was used to measure the EQE of our perovskite solar cells across a wavelength range of 300-800 nm.

RESULTS AND DISCUSSION Figure 1a represents the structure of our perovskite solar cells in the inverted cell structure using spray pyrolysis NiO as a hole transport layer (HTL) on an FTO coated glass substrate and solution-processed CH3NH3PbI3 perovskite as the absorber. The C60-bis ETL was spin-coated on the perovskite layer. The device was finished by the thermal evaporation of Ag as the top electrode. It has been reported before that the C60-bis ETL enables optimal alignment of energy levels between the organic semiconductors and electrode.

36-39

Figure 1b shows the energy band diagram of our

perovskite solar cells. Note that energy levels of C60-bis are determined by ultraviolet photoelectron spectroscopy (UPS) and ultraviolet-visible (UV-Vis) absorption spectroscopy measurements (Figure S1). The lowest unoccupied molecular orbital (LUMO) level of C60-bis is about -3.9 eV, almost the same as the LUMO level of CH3NH3PbI3, allowing the smooth electron transfer from CH3NH3PbI3 to Ag. Meanwhile, the highest occupied molecular orbital (HOMO) level of C60-bis is much lower than the HOMO level of CH3NH3PbI3, which can effectively block the holes from CH3NH3PbI3 to Ag. Therefore, C60-bis can be an efficient ETL for reducing charge carrier recombination and shunt currents. Figure 1c shows the molecular structures of C60-bis and Figure 1d shows the cross-sectional scanning electron microscopy (SEM) image of our perovskite solar cells with ultrathin transporter layer. It shows that the thicknesses of FTO and perovskite films are approximately ～340 nm and～350 nm, respectively. The ETL of C60-bis layer is about ～30 nm. The ultrathin NiO layer is not easily seen from this cross-sectional image. It can be seen that the perovskite and transporter layers have good integrity and uniformity, which are necessary for generating respectable photocurrents. The top view SEM image of 6


Page 6 of 21

Page 7 of 21

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


C60-bis on perovskite film was shown in Figure S2 (SI). It can be seen that our solution-processed C60-bis can effectively cover the perovskite films and get a smooth surface. Figure 2a shows a top-view SEM image of solution-processed perovskite film on the NiO-coated FTO substrate. It can be seen that the film is quite uniform and compact with an average grain size of 400-450 nm. Figure 2b shows the 3D image of the film surface morphology measured by using tapping mode atomic force microscope (AFM). The root mean square (RMS) roughness of film is only 11.3 nm. Moreover, one can also see that our one-step solution-processed perovskite layer is pinhole-free and sufficiently dense to prevent the penetration of C60-bis through the perovskite layer and directly contact NiO/FTO electrode, beneficial for the reduction of device leakage. The X-ray diffraction patterns in Figure 2c affirm that the perovskite film is crystalline, with the tetragonal structure and random orientation.

40

The peaks at 14.41o and 28.75o correspond to (110) and (220) planes, respectively. Meanwhile, it can also be found that a very small amount of PbI2 (peak at 12.6o) exists in the spectra of our perovskite films, which could effectively improve the device performances and reproducibility as reported previously.

41

The UV–vis

absorption spectrum and photoluminescence (PL) spectrum of the perovskite film is shown in Figure 2d. A broad absorption peak appears in the range of 500 - 800 nm. The emission peaks appearing approximately at the ～770 nm resulting from the PL of CH3NH3PbI3 are in accordance with the absorption tail state of CH3NH3PbI3, whose emission photon energy corresponds to the band gap of about 1.6 eV. 42 In order to understand the effect of C60-bis layer thickness on the device performance, the current density–voltage (J–V) characteristics of the devices fabricated with various C60-bis concentration under AM 1.5G 100 mW/cm2 illumination are measured, as shown in Figure 3a. The performance summary of corresponding devices is tabulated in Table 1 and the performance statistics (Voc, Jsc, FF and PCE) of these devices are shown in Figure S3 (SI). The devices with C60-bis inserted as the ETL exhibit simultaneous enhancement of all primary performance 7



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

parameters. The reference device without C60-bis has very poor performance and reproducibility because of uncontrollable electron extraction and hole blocking at the perovskite/Ag interface, showing a PCE of 4.07% with a Voc of 0.97 V, a Jsc of 7.9 mA/cm2, and an FF of 53%. This is evidenced by the larger leakage current of device under reverse bias, as shown in the dark J–V characteristics (Figure S4, SI). It is worth noting that the spin-coating technique is very advantageous since the materials can be uniformly coated on the substrates and meanwhile its cost is very low compared to other deposition method such as thermal evaporation technique. From Figure S5 (SI), it can be seen that there is no distinct difference in the surface roughness (root mean square (RMS) roughness) between bare CH3NH3PbI3 and C60-bis coated CH3NH3PbI3 using various concentration, and similar morphology appears in all samples. The variation of C60-bis concentration cannot strongly influence the Voc. However, remarkable changes of Jsc and FF have been observed. When the concentration of the C60-bis is 2 mg/ml, the efficiency of solar cell reaches a maximum value of 15.15%, with a Voc of 1.04 V, a Jsc of 20.7 mA/cm2, and an FF of 70.4%. It is believed that the C60-bis layer can effectively transfer electrons, block holes, and suppress charge recombination at the perovskite/Ag interface, leading to a significant enhancement of Jsc and FF. With further increasing the concentration of the C60-bis to 3 mg/ml, the device with 3 mg/ml C60-bis achieves a PCE of 12.71% with a Voc of 1.03 V, a Jsc of 18.0 mA/cm2, and an FF of 68%. It is obvious that the thicker C60-bis layers (3 mg/ml) should result in a reduction in device efficiency, primarily due to the decreased Jsc. Nevertheless, the devices with C60-bis generally have a negligibly low current leakage under reverse bias compared with the reference ones, as shown in the dark J–V characteristics (Figure S4, SI). Figure 3b shows the external quantum efficiency (EQE) spectra of various perovskite cells. The device using a 2 mg/ml C60-bis possesses the highest EQE, producing an EQE-integrated Jsc of 20.9 mA/cm2, in good agreement with Jsc obtained from the J–V curve. The obvious drop in the range of 650 - 750 nm for all EQE curves is likely ascribed to optical cavity effect,

43

which could be further improved by careful photon 8


Page 8 of 21

Page 9 of 21

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


management. It is well known that one key problem for current perovskite solar cells is the hysteresis effect of J–V curves, which strongly depends on the voltage scanning direction, the scanning rate and the device architecture.

44

Such hysteresis effect

usually results in an overestimation of the device efficiency. Figure 4a shows the J–V characteristics of the device with a C60-bis ETL under 100 mW/cm2 illumination by applying different voltage scanning directions. It can be seen that the hysteresis effect of our devices is very small. The forward-reverse PCE of our device is 14.95%, with a Voc of 1.06 V, a Jsc of 19.8 mA/cm2 and an FF of 71.1%, while the reverse-forward PCE is 14.84%, with a Voc of 1.05 V, a Jsc of 19.6 mA/cm2 and an FF of 71.7%. To estimate the accuracy of device performance, the steady-state efficiency measurement is a reliable method that reflects the actual performance under operation. Figure 4b shows the steady-state Jsc and PCE of the device with a C60-bis layer at a constant bias of 0.811 V under AM1.5G 100 mW/cm2 illumination. A steady-state Jsc of approximate 18 mA/cm2 and a stabilized PCE of 14.7% have been achieved. The devices without a C60-bis layer have serious hysteresis in the J–V curves (Figure S6, SI). Obvious reduced hysteresis and steady-state efficiency close to J–V efficiency in our these results indicate that our device contains less density of traps for electrons or holes,

45

and meanwhile the C60-bis layer can be an efficient and stable ETL in

perovskite solar cells application. The photoluminescence (PL) measurements are used to investigate the ability of extracting photo-generated carriers of the C60-bis layer from the perovskite absorber, since the C60-bis behaviors as an electrical extraction and transporting layers in our perovskite solar cells. The carrier extraction efficiency of PCBM and pristine CH3NH3PbI3 was also measured as a comparison in our perovskite solar cells. The CH3NH3PbI3 film shows a strongest PL peak at ～770 nm and a considerably greater degree of PL quenching displays when C60-bis is used on CH3NH3PbI3 film as compared to PCBM, as shown in Figure 5(a). It indicates that the utilization of C60-bis can improve the carrier collection and transport efficiency of devices, which is 9



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

consistent with the increased electrical conductivity. This also demonstrates the advantage of such an ETL layer in replacing PCBM for high-performance perovskite solar cells. Figure 5(b) compares the charge carrier lifetime (τ) measured by time-resolved photoluminescence (TRPL) in perovskite deposited on FTO and different ETLs deposited on FTO/NiO/perovskite. The TRPL decay curves were fitted by assuming an exponential decay model. The values of τ are 18, 2.2 and 1.5 ns for the FTO/NiO/perovskite sample, FTO/NiO/perovskite/PCBM/Ag sample, and the FTO/NiO/perovskite/C60-bis/Ag sample, respectively. Thus, it is clear that the insertion of such a thin C60-bis layer greatly enhances the electron extraction at the perovskite/Ag interface. This also suggests that the carrier extraction efficiency of C60-bis is stronger than PCBM. By optimizing the thickness of NiO layer (Figure S7, Table S1), the maximum PCE of our cells with a C60-bis ETL can reach 15.15%, with a Voc of 1.039 V, a Jsc of 20.71 mA/cm2, and a FF of 70.36%. The solar cells with a PCBM ETL show a PCE of 12.33%, with a Voc of 1.024 V, a Jsc of 17.91 mA/cm2 and a FF of 67.23%. The J–V characteristics and EQE spectrum are shown in Figure 6. The Jsc of the solar cells with C60-bis ETLs is higher than that of the cells with PCBM ETLs, due to the fact that C60-bis has a higher carrier extraction efficiency, extracting more photo-generated carriers from the perovskite absorber. The EQE curves shown in Figure 6b exhibits a very broad EQE plateau for all the devices in the wavelength range of 350-750 nm. The average EQE value of the device with a C60-bis ETL is over 70%, much higher that of the device with a PCBM ETL. The EQE-integrated Jsc can reach 20.5 mA/cm2 and 17.6 mA/cm2 for the solar cells with a C60-bis and PCBM ETL, respectively, in good agreement with those of J–V curves. The Voc, Jsc, FF and PCE of various devices are also illustrated in Figure S8 (SI). It can be seen that the utilization of a C60-bis ETL effectively improves the PCE of perovskite solar cells by increasing Jsc. To evaluate the reproducibility of our devices using an ultrathin C60-bis layer as the ETL, 40 devices with a C60-bis layer in several batches were fabricated. As shown in the histogram of the corresponding device data in Figure 6c, an average PCE of 13.52% 10


Page 10 of 21

Page 11 of 21

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


and a maximum PCE of 15.15% are achieved. The inset shows the PCE distribution of devices using a PCBM ETL. It can be seen that the average and maximum PCE of these perovskite solar cells are 10.9% and 12.3%, respectively. It suggests that our perovskite solar cells using a C60-bis ETL are significantly reproducible. Figure 7 shows the device parameters of PCE, Jsc, Voc and FF of our perovskite solar cells as a function of storage time under indoor humidity conditions. Very encouragingly, considering the purity of perovskite thin films, including the crystallinity and grain size, such as thin films fabricated from solution comprising single-crystals

47

, over 80% of its original efficiency of the device using the C60-bis

ETL can be dramatically preserved after 240 h of exposure in ambient condition (under humidity of ～30%). It can be inferred that the C60-bis ETL can effectively cover the perovskite layer to prevent the penetration of moisture or oxygen into perovskite layer and then improve the ambient stability.

CONCLUSIONS In summary, we have applied an ultrathin annealing-free C60-bis ETL to replace the commonly employed PCBM layer in the fabrication of solution-processed inverted perovskite solar cells. The devices with a C60-bis ETL exhibit an obviously higher short current density (Jsc) and therefore higher performance, which can be attributed to the effective electron extraction and hole blocking at the interface between the perovskite and C60-bis layers. Steady-state PL and TRPL results have clarified the increased charge carrier transfer at the interface by the application of C60-bis interlayer. A maximum efficiency of 15.15% and an average power conversion efficiency of 13.52% have been achieved for the perovskite solar cells with a C60-bis ETL. Moreover, it is found that the utilization of C60-bis ETL can effectively reduce the hysteresis effect of perovskite solar cell and increase the device stability under indoor humidity conditions. These results are of significance for the fabrication of stable and high PCE perovskite solar cells in atmosphere.

11



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

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: Ultraviolet photoelectron spectrometer (UPS) and ultraviolet-visible absorption spectroscopy (UV–Vis) of C60-bis，SEM image of C60-bis on perovskite films， statistics for photovoltaic parameters of the perovskite solar cells with different concentration of C60-bis layer, dark J-V characteristics of devices with and without the C60-bis layer, AFM images of varying thickness of C60-bis layers on MAPbI3, J-V curves, hysteresis without C60-bis layer, parameters statistics of the devices with different ETLs. AUTHOR INFORMATION Corresponding Author: Email: [email protected] (Xuegong Yu), [email protected] (Chang-Zhi Li) Present Address †

State Key Laboratory of Silicon Materials and School of Materials Science & Engineering, Zhejiang University, Hangzhou 310027, China. ‡ Department of Polymer Science & Engineering, Zhejiang University, Hangzhou 310027, China Author Contributions Jiabin Huang, Jiangsheng Xie and Yunhai Zhang do the experiments. Jiabin Huang wrote the draft. All authors discussed and revised the manuscript. Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS This work is supported by the National Natural Science Foundation of China (No. 61422404), Central basic scientific research in colleges and universities operating expenses, Program for Innovation Research Team in University of Ministry of Education of China and State Key Laboratory of Optoelectronic Materials and Technologies (Sun YatsenUnversity).

12


Page 12 of 21

Page 13 of 21

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


REFERENCES (1) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. Organometal Halide Perovskite as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 2009, 131, 6050−6051. (2) Stranks, S. D.; Snaith, H. J. Metal-Halide Perovskites for Photovoltaic and Light-Emitting Devices. Nat. Nanotechnol. 2015, 10, 391-402. (3) Kim, H.-S.; Lee, C.-R.; Im, J.-H.; Lee, K.-B.; Moehl, T.; Marchioro, A.; Moon, S.-J.; Humphry-Baker, R.; Yum, J.-H.; Moser, J. E.; Grätzel, M.; Park, N.-G. Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%. Sci. Rep. 2012, 2, 591. (4) Kojima, A.; Ikegami, M.; Teshima, K.; Miyasaka, T. Highly Luminescent Lead Bromide Perovskite Nanoparticles Synthesized with Porous Alumina Media. Chem. Lett. 2012, 41, 397-399. (5) 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. (6) deQuilettes, D. W.; Vorpahl, S. M.; Stranks, S. D.; Nagaoka, H.; Eperon, G. E.; Ziffer, M. E.; Snaith, H. J.; Ginger, D. S. Impact of Microstructure on Local Carrier Lifetime in Perovskite Solar Cells. Science. 2015, 348, 683-686. (7) Wehrenfennig, C. G.; Eperon, E.; Johnston, M. B.; Snaith, H. J.; Herz, L. M. High Charge Carrier Mobilities and Lifetimes in Organolead Trihalide Perovskites. Adv. Mater. 2014, 26, 1584-1589. (8) Bai, S.; Jin, Y.; Gao, F. Organometal Halide Perovskites for Photovoltaic Applications. Tiwari, A.,Uzan, L., Eds.; Wiley: Hoboken, NJ, 2015, Chapter 1310.1002/9781118998977.ch13. (9) Eperon, G. E.; Stranks, S. D.; Menelaou, C.; Johnston, M. B.; Herz, L. M.; Snaith, H. J. Formamidinium Lead Trihalide: A Broadly Tunable Perovskite for Efficient Planar Heterojunction Solar Cells. Energy Environ. Sci. 2014, 7, 982−988. (10) Miyata, A.; Mitioglu, A.; Plochocka, P.; Portugall, O. J.; Wang, T.-W.; Stranks, S. D.; Snaith, H. J.; Nicholas, R. J. Direct Measurement of the Exciton Binding Energy and Effective Masses for Charge Carriers in Organic-Inorganic Trihalide Perovskites. Nat. Phys. 2015, 11, 582-587. (11) Liu, M. Z.; Ohnston, M. B.; Snaith, H. J. Efficient Planar Heterojunction Perovskite Solar Cells by Vapour Deposition. Nature. 2013, 501, 395-398. (12) Jeon, N. J.; Noh, J. H.; Kim, Y. C. Solvent Engineering for High-Performance Inorganic–Organic Hybrid Perovskite Solar Cells. Nature Mater. 2014, 13, 897-903. (13) 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 Perovskite-Sensitized Solar Cells. Nature. 2013, 499, 316-319. (14) Zhao, D.; Ke, W.; Gricea, C. R.; Cimarolia, A. J.; Tana, X.; Yangb, M.; Collinsa, R. W.; Zhang, H.; Zhu, K.; Yan. Y. Annealing-Free Efficient Vacuum-Deposited Planar Perovskite Solar Cells with Evaporated Fullerenes as Electron-Selective Layers. Nano Energy. 2016, 19, 88-97. (15) Jeng, J.-Y.; Chiang, Y.-F.; Lee, M.-H.; Peng, S.-R.; Guo, T.-F.; Chen, P.; Wen, 13



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

T.-C. CH3NH3PbI3 Perovskite/Fullerene Planar-Heterojunction Hybrid Solar Cells. Adv. Mater. 2013, 25, 3727-3732. (16) Docampo, P.; Ball, J. M.; Darwich, M.; Eperon, G. E.; Snaith, H. J. Efficient Organometal Trihalide Perovskite Planar-Heterojunction Solar Cells on Flexible Polymer Substrates. Nat. Commun. 2013, 4, 2761-2766. (17) You, J.; Hong, Z.; Yang, Y. M.; Chen, Q.; Cai, M.; Song, T.-B.; Chen, C.-C.; Lu, S.; Liu, Y.; Zhou, H.; Yang. Y. Low-Temperature Solution-Processed Perovskite Solar Cells with High Efficiency and Flexibility. ACS Nano. 2014, 8 (2), 1674-1680. (18) Heo, J. H.; Im, S. H.; Noh, J. H.; Mandal, T. N.; Lim, C.-S.; Chang, J. A.; Lee, Y. H.; Kim, H.-J.; Sarkar, A.; Nazeeruddin, M. K.; Grätzel, M.; Seok. S. I. Efficient Inorganic-Organic Hybrid Heterojunction Solar Cells Containing Perovskite Compound and Polymeric Hole Onductors. Nature Photon. 2013, 7, 486-491. (19) Heo, J. H.; Han, H. J.; Kim, D.; Ahn, T. K.; Im, S. H. Hysteresis-Less Inverted CH3NH3PbI3 Planar Perovskite Hybrid Solar Cells with 18.1% Power Conversion Efficiency. Energy Environ. Sci. 2015, 8, 1602-1608. (20) Liang, P. W.; Liao, C. Y.; Chueh, C. C.; Zuo, F.; Williams, S. T.; Xin, X. K.; Lin, J.; Jen. A. K.-Y. Additive Enhanced Crystallization of Solution-Processed Perovskite for Highly Efficient Planar-Heterojunction Solar Cells. Adv. Mater. 2014, 26, 3748-3754. (21) Zuo, F.; Williams, S. T.; Liang, P. W.; Chueh, C. C.; Liao, C. Y.; Jen. A. K.-Y. Binary-Metal Perovskites toward High-Performance Planar-Heterojunction Hybrid Solar Cells. Adv. Mater. 2014, 26, 6454-6460. (22) Liang, P. W.; Chueh, C. C.; Williams, S. T.; Jen. A. K.-Y. Roles of Fullerene-Based Interlayers in Enhancing the Performance of Organometal Perovskite Thin Film Solar Cells. Adv. Energy Mater. 2015, 5, 1402321. (23) Park, J. H.; Seo, J.; Park, S.; Shin, S. S.; Kim, Y. C.; Jeon, N. J.; Shin, H. W.; Ahn, T. K.; Noh, J. H.; Yoon, S. C.; Hwang, C. S.; Seok, S. I. Efficient CH3NH3PbI3 Perovskite Solar Cells Employing Nanostructured p-Type NiO Electrode Formed by a Pulsed Laser Deposition. Adv. Mater. 2015, 27, 4013-4019. (24) Chen, W.; Wu, Y.; Yue, Y.; Liu, J.; Zhang, W.; Yang, X.; Chen, H.; Bi, E.; Ashraful, I.; Grätzel, M.; Han. L. Y. Efficient and Stable Large-Area Perovskite Solar Cells with Inorganic Charge Extraction Layers. Science. 2015, 350, 944-948. (25) Li, Y. W.; Zhao, Y.; Chen, Q.; Yang, Y. (Michael); Liu, Y. S.; Hong, Z. R.; Liu, Z. H.; Hsieh, Y.-T.; Meng, L.; Li, Y. F.; Yang, Y. Multifunctional Fullerene Derivative for Interface Engineering in Perovskite Solar Cells. J. Am. Chem. Soc. 2015, 137, 15540−15547. (26) 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. (27) 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 14


Page 14 of 21

Page 15 of 21

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) Jeng, J-Y.; Chen, K.-C.; Chiang, T.-Y.; Lin, P.-Y.; Tsai, T.-D.; Chang, Y.-C.; T Guo,.-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. (29) Wang, K. C.; Jeng, J. Y.; Shen, P. S.; Chang, Y. C.; Diau, E. W.; Tsai, C. H.; Chao, T. Y.; Hsu, H. C.; Lin, P. Y.; Chen, P.; Guo, T. F.; Wen, T. C. p-Type Mesoscopic Nickel Oxide/Organometallic Perovskite Heterojunction Solar Cells. Sci. Rep. 2014, 4, 4756. (30) Wojciechowski, K.; Stranks, S. D.; Abate, A.; Sadoughi, G.; Sadhanala, A.; Kopidakis, N.; Rumbles, G.; Li, C.-Z.; Friend, R. H.; Jen, A. K.-Y.; Snaith. H. J. Heterojunction Modification for Highly Efficient Organic–Inorganic Perovskite Solar Cells. ACS Nano. 2014, 8, 12701–12709. (31) Kim, J.; Kim, G.; Kim, T. K.; Kwon, S.; Back, H.; Lee, J.; Lee, S. H.; Kang, H.; Lee, K.; Efficient Planar-Heterojunction Perovskite Solar Cells Achieved via Interfacial Modification of A Sol–gel ZnO Electron Collection Layer. J. Mater. Chem. A. 2014, 2, 17291-17296. (32) Ryu, S.; Seo, J.; Shin, S. S.; Kim, Y. C.; Jeon, N. J.; Noh, J. H.; Seok, S. I. Fabrication of Metal-Oxide-Free CH3NH3PbI3 Perovskite Solar Cells Processed at Low Temperature. J. Mater. Chem. A. 2015, 3, 3271-3275. (33) Zhu, Z.; Chueh, C.-C.; Lin, F.; A. Jen. K.-Y. Enhanced Ambient Stability of Efficient Perovskite Solar Cells by Employing a Modified Fullerene Cathode Interlayer. Adv. Sci. 2016, 1600027. (34) Wojciechowski, K.; Leijtens, T.; Siprova, S.; Schlueter, C.; Hörantner, M. T.; Wang, J. T.-W. Li, C.-Z.; Jen, A. K.Y.; Lee, T.-L.; Snaith, H. J. C60 as An Efficient n-Type Compact Layer in Perovskite Solar Cells. J. Phys. Chem. Lett. 2015, 6, 2399–2405. (35) Grancini, G.; Kumar, R. S. S.; Abrusci, A.; Yip, H.-L.; Li, C.-Z.; Jen, A.-K. Y.; Lanzani, G.; Snaith, H. J. Boosting Infrared Light Harvesting by Molecular Functionalization of Metal Oxide/Polymer Interfaces in Efficient Hybrid Solar Cells. Adv. Funct. Mater. 2012, 22, 2160-2166. (36) Chueh, C.-C.; Chien, S.-C.; Yip, H.-L.; Salinas, J. F.; Li, C.-Z.; Chen, K.-S.; Chen, F.-C.; Chen, W.-C.; Jen, A. K. Y. Toward High-Performance Semi-Transparent Polymer Solar Cells: Optimization of Ultra-Thin Light Absorbing Layer and Transparent Cathode Architecture. Adv. Energy Mater. 2013, 3, 417-423. (37) Li, C.-Z.; Chueh, C.-C.; Yip, H.-L.; O'Malley, K. M.; Chen, W.-C.; Jen, A. K.-Y. Effective Interfacial Layer to Enhance Efficiency of Polymer Solar Cells via Solution-Processed Fullerene-Surfactants. J. Mater. Chem. 2012, 22, 8574–8578. (38) O’Malley, K. M.; Li, C.-Z.; Yip, H.-L.; Jen, A. K.-Y. Enhanced Open-Circuit Voltage in High Performance Polymer/Fullerene Bulk-Heterojunction Solar Cells by Cathode Modification with a C60 Surfactant. Adv. Energy Mater. 2012, 2, 82–86. (39) Jen, K.-Y.; Yip, H.-L.; Li, C.-Z. United Stated Patent, 2015, US009214574B2. (40) Malinkiewicz, O.; Yella, A.; Lee, Y. H.; Espallargas, G. M.; Graetzel, M.; Nazeeruddin, M. K.; Bolink, H. J. Perovskite Solar Cells Employing Organic Charge-Transport Layers. Nat. Photon. 2014, 8, 128-132. 15



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

(41) 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. (42) Jung, H. S.; Park, N.-G. Perovskite Solar Cells: From Materials to Devices. Small. 2014, 11, 10-25. (43) Lin, Q.; Armin, A.; Nagiri, R. C. R.; Burn, P. L.; Meredith, P. Electro-Optics of Perovskite Solar Cells. Nat. Photon. 2015, 9, 106-112. (44) Snaith, H. J.; Abate, A.; Ball, J. M.; Eperon, G. E.; Leijtens, T.; Noel, N. K.; Stranks, S. D.; Wang, J. T.-W.; Wojciechowski, K.; Zhang, W. Anomalous Hysteresis in Perovskite Solar Cells. J. Phys. Chem. Lett. 2014, 5, 1511-1515. (45) Yin, W.-J.; Shi, T.; Yan, Y. Unusual Defect Physics in CH3NH3PbI3 Perovskite Solar Cell Absorber. Appl. Phys. Lett. 2014, 104, 063903. (46) Ahn, N.; Son, D.-Y.; Jang, I.-H.; Kang, S. M.; Choi, M.; Park, N.-G. Highly Reproducible Perovskite Solar Cells with Average Efficiency of 18.3% and Best Efficiency of 19.7% Fabricated via Lewis Base Adduct of Lead (II) Iodide. J. Am. Chem. Soc. 2015, 137, 8696-8699. (47) Yen, H.-J.; Liang, P.-Wei; Chueh, C.-C.; Yang, Z.; Jen, A. K.-Y.; Wang, H.-L. Large Grained Perovskite Solar Cells Derived from Single-Crystal Perovskite Powders with Enhanced Ambient Stability. ACS Appl. Mater. Interfaces. 2016, 8, 14513−14520. (48) Huang, J.B.; Yu, X.G.; Xie, J.S.; Xu, D.K.; Tang, Z.G.; Cui, C and Yang, D.R. Ambient Engineering for High Performance Organic-Inorganic Perovskite Hybrid Solar Cells. ACS Appl. Mater. & Interfaces, 2016, 8, 21505-21511.

(a)

(b)

(c)

(d)

C60-bis

16


Page 16 of 21

Page 17 of 21

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


Figure 1. (a) Schematic of device structure. (b) Energy level diagram of the solar cell. (c) Molecular structures of C60-bis and (d) cross-sectional SEM image of the studied perovskite solar cell.

(a)

(b)

(c)

(d)

Rq=11.3nm

Figure 2. (a) SEM image and (b) tapping-mode AFM image of a solution-processed perovskite film on a NiO-deposited FTO substrate, (c) X-ray diffraction patterns for perovskite films on FTO and FTO patterns for reference, and (d) UV-vis absorption spectrum and PL spectrum of the perovskite film. Table 1. Summary of performance metrics of the devices using various concentration of C60-bis as the ETL. 2

Voc (V)

Jsc (mA/cm )

FF (%)

PCE (%)

w/o C60-bis

0.97

7.9

53.2

4.07

1 mg/ml

0.95

19.2

58.1

10.58

2 mg/ml

1.04

20.7

70.4

15.15

3 mg/ml

1.03

17.9

68.5

12.71

17



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

(a)

(b)

Figure 3. (a) J–V characteristics under AM 1.5G 100 mW/cm2 illumination and (b) EQE spectra of perovskite solar cells with varying concentration of the C60-bis.

(a)

(b)

Figure 4. (a) J–V characteristics of the devices using 2 mg/ml C60-bis as ETL under 100 mW/cm2 illumination under different voltage scanning direction: reverse–forward and forward–reverse and (b) steady-state Jsc and PCE of the device using 2 mg/ml C60-bis as ETL at a constant bias of 0.811 V under 100 mW/cm2 illumination.

(a)

(b)

Figure 5. (a) Steady-state PL measurements from samples photoexcited at 635 nm; (b) TRPL measurements comparing charge carrier lifetime in the perovskite films deposited on FTO/NiO and on FTO/NiO/Perovskite/C60-bis (2mg/ml) and FTO/NiO/Perovskite/PCBM, respectively.

18


Page 18 of 21

Page 19 of 21

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


(a)

(b)

(c)

Figure 6. (a) J–V characteristic of our best-performing perovskite solar cells under AM1.5G 100 mW/cm2 illumination using C60-bis and PCBM as ETLs, respectively; (b) EQE spectrum of our best-performing perovskite solar cells using 2 mg/ml C60-bis and PCBM as the ETLs; (c) Histogram of 40 devices using 2 mg/ml C60-bis as the ETL from several fabrication batches of solar cells. The inset is the comparison of devices with the PCBM as the ETL.

19



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

(a)

(b)

(c)

(d)

Figure 7. Stability of parameters of (a) PCE; (b)Voc; (c)Jsc and (d)FF of perovskite solar cells with a C60-bis and PCBM ETL after 240 h of exposure in ambient condition.

20


Page 20 of 21

Page 21 of 21

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


O O

Me O

I

O

Me N

O

O O

O

O

O

O

O O

O

O

O N O

Me

I

Me

O

C60-bis

TOC graphic

21


Fulleropyrrolidinium Iodide As an Efficient Electron Transport Layer for

Recommend Documents