- Email: [email protected]
Pentacene as a hole transport material for high performance planar perovskite solar cells
Accepted Manuscript Pentacene as a hole transport material for high performance planar perovskite solar cells Xiude Yang, Gang Wang, Debei Liu, Yanqing Yao, Guangdong Zhou, Ping Li, Bo Wu, Xi Rao, Qunliang Song PII:
S1567-1739(18)30152-4
DOI:
10.1016/j.cap.2018.05.022
Reference:
CAP 4763
To appear in:
Current Applied Physics
Received Date: 10 April 2018 Revised Date:
22 May 2018
Accepted Date: 23 May 2018
Please cite this article as: X. Yang, G. Wang, D. Liu, Y. Yao, G. Zhou, P. Li, B. Wu, X. Rao, Q. Song, Pentacene as a hole transport material for high performance planar perovskite solar cells, Current Applied Physics (2018), doi: 10.1016/j.cap.2018.05.022. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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A cost-effective and efficient organic semiconductor pentacene was developed as a hole transport layer material to substitute classical PEDOT:PSS for planar perovskite solar cells. The pentacene based device exhibits the comparable performance to the PEDOT:PSS based device, which is mainly attributed to the high-efficiency charge extraction derived from the high-quality perovskite film and favorable energy-level alignment together with a desired downward band bending.
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Pentacene as a hole transport material for high performance planar perovskite solar cells Xiude Yang a, b,c #, Gang Wang a,b #, Debei Liu a,b, Yanqing Yao a,b, Guangdong Zhou a,b, Ping Li c, Bo Wu c, Xi Rao a,b, Qunliang Song a,b * Institute for Clean Energy & Advanced Materials (ICEAM), Southwest University, Chongqing 400715, P. R. China
b.
Chongqing Key Laboratory for Advanced Materials and Technologies of Clean Energy, Chongqing 400715, P. R. China
c.
School of Physics and Electronic science, Zunyi Normal College, Zunyi 563002, P. R. China Xiude Yang and Gang Wang contributed equally to this work
＃
*
E-mail: [email protected]
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a.
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Abstract：A cost-effective and efficient organic semiconductor pentacene was developed as a hole transport layer (HTL) material to replace classical PEDOT:PSS for planar perovskite solar cells
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(PSCs). As expected, the pentacene based device exhibits power conversion efficiency (PCE) of 15.90% (Jsc of 19.44 mA/cm2, Voc of 1.07 V, and FF of 77%), comparable to the PEDOT:PSS based device (PCE of 15.65%, Jsc of 18.78 mA/cm2, Voc of 1.07 V, and FF of 77%) under the same experimental conditions. The excellent performance of vacuum deposited pentacene is
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mainly attributed to the high efficient charge extraction and transfer in device due to the high-quality perovskite film grown on the top of pentacene substrate and a favorable energy-level alignment together with a desired downward band bending formed at the perovskite/pentacene interface. Our research has confirmed that pentacene could be served as a promising HTL material
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to achieve effective and potentially economical planar type PSCs.
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Keywords: pentacene; hole transport layer; perovskite solar cells
1. Introduction
Recently, organic-inorganic hybrid perovskite compounds considered as a class of
approximatively ideal light absorbers have been extensively focused and studied on solar cells. They have unique features such as the high absorption coefficient across visible spectrum, low trap-state density, long carrier diffusion length and lifetime. [1-3] Just over the past several years, perovskite solar cells (PSCs) with multiple architectures have been developed rapidly and the power conversion efficiency (PCE) has already exceeded 20% [4,5] since perovskite was firstly
ACCEPTED MANUSCRIPT reported for dye-sensitized solar cell with a PCE of mere 3.8%, [6] showing vigorous development trend
and
potential
application
prospect.
(N,N’-di-p-methoxyphenylamine)-9,9’-spirobifluorene
Especially,
(spiro-OMETAD)
2,2’,7,7’-tetrakis was
applied
for
preparing the all-solid PSC, which represented a significant breakthrough in device's development
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from original mesoporous structure to newly planar structure. [7] Currently, a large number of researches have indicated that the PCE of perovskite based solar cells is not only determined by the fabrication processes and conditions, but also considerably depends on superior hole transport layer (HTL) and electron transport layer (ETL) materials for
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efficient carrier extraction in devices. [8] Correspondingly, intensive efforts have been dedicated to exploit high-performance PSCs via seeking more better materials as efficient ETL and HTL. To
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date, there are mainly two prototypes of planar architectures in PSC community: conventional n-i-p structure with transparent cathode/ETL (n)/perovskite (i)/HTL (p)/anode [9] and so called “inverted” p-i-n structure with transparent anode/HTL (p)/perovskite (i)/ETL (n)/cathode [10]. As for n-i-p type PSCs, in previous studies, many HTL materials such as spiro-OMETAD,
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polytriarylamine (PTAA) and NiO, which were sandwiched between anode and perovskite, increased PCE significantly. [11-14] Similarly, for inverted p-i-n type PSCs, inspired by the organic solar cells (OSCs), some excellent photoelectric materials formerly employed in OSCs also served as HTLs for PSCs to distinctly promote the device efficiency. For instance,
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Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) (PEDOT:PSS) was commonly utilized as a HTL and has obtained favorable device performance. [15,16] As such, high efficient CuPc,
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P3HT and rubrene HTL based PSCs were demonstrated sequentially by the following literatures. [2, 17-19] Among all of HTL materials mentioned above, although both the use of spiro-OMeTAD in n-i-p structure and PEDOT:PSS in p-i-n structure are proved to be most successful, their own issues are also destructive to develop PSC devices. Spiro-OMeTAD requires a complex and strict doping strategy, which increases the overall cost and meanwhile induces the device instability and unrepeatability. [20] While PEDOT:PSS would corrode the indium-tin oxide (ITO) electrode, causing migration of indium into PEDOT:PSS, and its hygroscopic nature tends to degrade the resultant devices owing to the water uptake. [21] Accordingly, searching more stable and
ACCEPTED MANUSCRIPT economically viable HTL materials for PSCs to promote effective exciton dissociation/charge extraction is still a very important task. Pentacene with a molecular structure shown in Fig. 1a is a superior p-type semiconductor, which was vastly employed in organic field effect transistors [22,23] and OSCs [17,18] in the past.
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In recent reports, its derivatives were verified as high effective HTLs for fabricating PSCs. [24,25] Particularly, Gao et al. [26] have found that the pentacene/CH3NH3PbI3 interface could form a suitable energy-level diagram to efficiently facilitate charge transportation, thereout forecasting that pentacene is an unquestionably matched HTL material for the above two type of PSCs.
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However, the related experiment investigation on device performance to pentacene HTL based PSCs hasn't been reported so far.
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In this work, by adopting the physical vapor deposition (PVD) system, a thin pentacene HTL for PSC has been deposited on ITO to take place of classical PEDOT:PSS HTL in the reference device with a planar p-i-n structure of ITO/PEDOT:PSS/perovskite/fullerene derivatives ([6,6]-phenyl-c61-butyric
acid
methyl
ester
(PCBM)/C60
(10
nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (4 nm)/Ag. A champion PCE of
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15.90% with a best short-circuit current (Jsc) of 19.44 mA/cm2 is acquired in the device with pentacene HTL, whose performance is almost the same as the reference device with PEDOT:PSS HTL (PCE of 15.65% and Jsc of 18.89 mA/cm2) under the same fabrication conditions.
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Additionally, both the high-quality perovskite film deposited on pentacene layer and the optimized energy-level alignment formed at the perovskite/pentacene interface attested that pentacene could
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experimentally serve as a viable HTL candidate for efficient perovskite-based solar cells.
Experiment
2.1 Materials
N,N-dimethylformide (DMF), dimethyl sulfoxide (DMSO), chlorobenzene (CB) and
pentacene were bought from Sigma-Aldrich. PEDOT:PSS, methyl ammonium iodide (MAI), lead iodide (PbI2), lead chloride (PbCl2), PCBM and BCP were purchased from Xi 'an Polymer Light Technology Corp (China).The perovskite precursor solution was prepared with 0.14 M PbCl2, 1.26 M PbI2 and 1.4 M MAI dissolved in a co-solvent of DMSO and DMF (vol. ratio = 1: 9) in a glove
ACCEPTED MANUSCRIPT box and stirred overnight under room temperature. 2.2 Device fabrication The schematic architecture of PSC and corresponding energy level are illustrated in Figs.1b and c, respectively. The preparation process of PSCs can be divided into three parts: substrate
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cleaning, function layers and electrode growth. The details are described as follows:
Fig.1 (a) The molecule structure of pentacene, (b) the architecture of the PSCs with pentacene HTL, and (c) the corresponding energy level diagram of devices.
Substrate cleaning: ITO substrate was sequentially cleaned in an ultrasonic bath with a detergent of Decon 90, acetone, deionized water and ethanol, then dried under N2 stream. The growth of functional layers: A thin pentacene layer (30 nm) was deposited on ITO by thermal evaporation under high-vacuum, which was monitored by a quartz crystal. Afterwards, the filtered perovskite precursor was grown on pentacene by one-step spin-coating method at 1000 rpm for 3 s and 4000 rpm for 20 s, then 200 µL CB dropped quickly in the second step, and then
ACCEPTED MANUSCRIPT the film followed by heating on a hotplate at 60 °C for 2 min and 85°C for 25 min. PCBM from CB solution with a concentration of 20 mg/mL was spin-coated on perovskite layer with a speed of 4000 rpm for 40 s. All above spin-coating processes were manipulated inside a N2-filled glove box.
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The growth of electrode: Finally, a 10 nm C60, a 4 nm BCP and a 100 nm Ag electrode were sequentially deposited through a shadow mask in the same way as pentacene. The active cell area was 0.09 cm2. 2.3 Characterization
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The morphology and cross-section of the as-prepared perovskite films deposited on PEDOT:PSS or pentacene were observed by using a field-emission scanning electron microscopy
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(SEM, JSM-6700F). Their corresponding crystal structures were examined by an X-ray diffraction system (Shimadzu XRD-7000). And the UV-Vis absorption measurements were carried out using Shimadzu UV-2550 spectrometer.
The current density-voltage (J–V) characteristics for the developed PSCs were measured by
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Keithley 2400 source meter in conjunction with 100 mW/cm2 (AM 1.5 G) simulated sunlight from a solar simulator (Newport 94043A). During the measurement, reverse scan (from 1.2 to -1.2 V) and forward scan (from -1.2 to 1.2 V) were performed with a voltage step of 10 mV and 0 ms delay time. The external quantum efficiency (EQE) of devices was calculated from photocurrent
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generated from the modulated monochromatic light by a lock-in amplifier (SR-830). Both the J–V and EQE characteristics were tested in the N2-filled glove box.
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Transient photovoltage (TPV) tests of the as-prepared cells were performed directly in series
with an oscilloscope (Agilent DSO-X 3102A). During the measurements, the input impedance of oscilloscope was switched to 1 MΩ and the 532 nm pulsed laser was used as the excitation light source.
3. Results and discussion 3.1 XRD and SEM characterization The XRD patterns of perovskite films deposited on pentacene or PEDOT:PSS are shown in Fig. 2. The main diffraction peaks at 14.14°, 28.48° and 31.92°, which respectively corresponds to
ACCEPTED MANUSCRIPT the (110), (220) and (310) lattice plane of MAPbI3 crystal structure are observed, evidencing the formation of typical tetragonal phase in perovskite films as previously reported. [27,28] It is worth noting that although very weaker PbI2 diffraction peak could be found around 12.5°, the residual PbI2 would passivate perovskite grain boundaries to boost the VOC of MAPbI3 devices, which was
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demonstrated in previous report [29]. And, none of MAPbCl3 diffraction peaks is discovered since most chloride ions escape from NH3CH3Cl during annealing process. [28,30] Furthermore, the intensity of diffraction peaks of (110) and (220) faces on pentacene is slightly lower than that on PEDOT:PSS, reflecting enhanced crystallinity of perovskite film on PEDOT:PSS. This is likely
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due to the faster crystal growth of film during annealing stage, which is facilitated as a result of the moisture absorbed by PEDOT:PSS during spin-coated process in air. [31]
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Figs. 3a,b display the SEM images of perovskite films deposited on pentacene and PEDOT:PSS, respectively. Excitedly, the perovskite film on pentacene shows a larger average grain size than that on PEDOT:PSS, which is more beneficial for charge carrier transportation. This is because the smaller grain size leads to a larger boundary density, and consequently more
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defect states generated at grain boundaries would negatively affect carrier transfer, eventually reducing the device performance due to trap filling of the photo-induced electrons and an accumulation of holes. [32-35] Besides, the perovskite film on pentacene also exhibits the relatively more smoother surface and higher coverage compared with film on PEDOT:PSS. Also,
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in cross-section SEM images (see Fig.S1 in supporting information), a ~450 nm perovskite layer over a ~30 nm PEDOT:PSS HTL or ~30 nm pentacene HTL are clearly observed. Hence, we
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conclude that the formation of a high-quality perovskite film on pentacene promotes an efficient charge extraction.
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Fig.2 The XRD patterns of perovskite films deposited on pentacene and PEDOT:PSS, respectively.
Fig.3 The SEM images of perovskite films deposited respectively on (a) pentacene, and (b) PEDOT:PSS.
3.2 TPV measurements of PSCs To examine the effectivity of charge extraction in devices, TPV tests were used to assess the
lifetime of the free carriers in the two different PSCs. The longer the lifetime of the free carriers is, the longer the TPV decay-time is. Fig. 4 displays the normalized TPV in the PSCs with PEDOT:PSS HTL and pentacene HTL. The pentacene based device shows a slight longer photovoltage decay (~1.13 ms) to the PEDOT:PSS based reference device (~0.88 ms). The results indicate that they have an approximately equal lifetime of charge carriers, which proves the
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PEDOT:PSS device.
Fig.4 TPV measurements of PSCs with PEDOT:PSS HTL or pentacene HTL.
3.3 Photovoltaic performance of PSCs
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To further verify the performance and feasibility of pentacene as an efficient HTL in p-i-n type PSCs, the J-V characteristics of two devices with different HTLs are shown in Fig. 5a, and their corresponding photovoltaic parameters are listed in Table 1. The reference device with PEDOT:PSS HTL yields a PCE of 15.65% with Jsc, open circuit voltage (Voc) and fill factor (FF)
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of 18.78 mA/cm2, 1.07 V and 77%, respectively, which shows consistent performance similar to the results in previous studies. [15,16] To our surprise, under the same experimental conditions,
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the device with pentacene HTL also exhibits a laudable performance with PCE of 15.90%, Jsc of 19.44 mA/cm2, Voc of 1.07 V and FF of 77%, of which all device parameters are almost equal to the reference device with PEDOT:PSS HTL. The EQE spectrum measurements of two different HTL devices were conducted to confirm the Jsc, as presented in Fig. 5b. The calculated integral current densities of the devices with pentacene HTL and with PEDOT:PSS HTL (see Fig.S2 in supporting information) are 19.22 mA/cm2 and 19.00 mA/cm2, respectively, consisting with the aforementioned J-V measurement results. Note that, though the buffer layers are different, the UV-Vis light absorbance of the perovskite films are similar, as shown in Fig.S3 (supporting
ACCEPTED MANUSCRIPT information). In addition, Figs. 5c, d show the forward and reverse J-V curves of PSCs with pentacene and with PEDOT:PSS HTL, respectively. Fortunately, there is no obvious hysteresis emerging in the two devices, suggesting that both of them own good balanced electron and hole flux as well as less surface traps. [2, 36-38] Furthermore, the stability tests for two different HTL
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devices were carried out for about 200 s inside a N2-filled glove box. The test results show that both PCEs have a very slight decay at the maximum power point, as shown in Fig.S4 (supporting information). Apparently, pentacene could contribute the same effort as PEDOT:PSS for inverted PSCs. Therefore, there is no doubt that pentacene can be adopted as a practicable HTL candidate
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to substitute PEDOT:PSS for fabricating efficient inverted perovskite based solar cells.
Fig. 5 (a) J-V curves of devices with pentacene HTL and with PEDOT:PSS HTL, respectively. (b) EQE spectra of the two corresponding devices. The forward and reverse J-V curves of device (c) with pentacene HTL, and (d) with PEDOT:PSS HTL. Table 1. Photovoltaic performance of the devices with pentacene HTL and with PEDOT:PSS HTL. HTL
Scan direction
Voc (V)
Jsc (mA/cm2)
FF (%)
PCE (%)
PEDOT:PSS
Forward
1.07
18.89
77
15.65
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pentacene
Reverse
1.07
18.78
77
15.50
Forward
1.07
19.22
77
15.85
Reverse
1.07
19.44
76
15.90
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By comprehensive comparison and analysis with PEDOT:PSS HTL device, the outstanding performance of device with pentacene HTL maybe mainly ascribed to two aspect factors as follows:
On one hand, as previous studies have reported that there is a positive correlation between the
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device performance and the quality of perovskite films in device, [39,40] thus we deduce that the high performance of pentacene HTL device should partly come from the formations of a good
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tetragonal phase crystallinity and a high-quality morphology of perovskite film, as evidenced from XRD and SEM characterization displayed in Figs. 3a,b. Especially, the larger grain size, better coverage and higher flatness of perovskite film grown on pentacene result in less grain boundaries and trap state density, [32,33] which is favor of efficient charge extraction and transportion in
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device, consequently a slight higher PCE and Jsc are achieved with respect to the PEDOT:PSS HTL device. The effectiveness of charge-extraction is also revealed by the aforementioned TPV measurements.
More importantly, the matching energy-level alignment and the effect of downward band
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bending formed at perovskite/pentacene interface are also responsible for the expected performance of device with pentacene HTL, which is supported by XPS and UPS measurement
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results from previous research. [26] Firstly, from the energy-level diagram of device (in Fig.1c), it clearly shows that the HOMO level of pentacene is energetically favorable with regards to the valence band of perovskite in device, merely 0.2 eV energy difference in comparison with PEDOT:PSS of -5.2 eV. Moreover, on basis of the report from Ref.26, it is very interesting to note that a downward band bending together with an interfacial dipole at the pentacene side is observed due to the charge exchange at interface. [2, 41] As a consequence, a rather low HOMO-VBM offset ∆Ev and a large LUMO-CBM offset ∆Ec at the perovskite/pentacene interface are created, which can be depicted in Fig.6. Eventually, this desirable energy level alignment and downward
ACCEPTED MANUSCRIPT band bending potentially facilitate hole extraction from perovskite to the pentacene HTL, and meanwhile effectively block unwanted electron transfer from perovskite to pentacene. All these results have further confirmed that pentacene can be employed as a suitable HTL material, which
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is worth being exploited in inverted p-i-n planar PSCs.
Fig.6 The energy level diagram at the perovskite CH3NH3PbI3/pentacene interface
4. Conclusion
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In summary, we have developed a cost-effective and efficient organic semiconductor pentacene as a HTL material for inverted PSCs without the usage of PEDOT:PSS, additional
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dopants/additives as well as high temperature sintering. Remarkably, the admirable performance of pentacene based device is comparable to the classical PEDOT:PSS based device under the same experiment conditions. This is mainly attributed to the high efficient charge extraction and transfer derived from the high-quality perovskite film grown on top of the pentacene with an appropriate grain size, good coverage and flatness, and a favorable energy-level alignment with desired downward band bending formed at the perovskite/pentacene interface. In such a device, a champion efficiency as high as 15.90% and the highest Jsc of 19.44 mA/cm2 are obtained. All these results convincingly demonstrate that pentacene can be served as a promising HTL material to achieve efficient and economical thin film photovoltaic devices. This study also indicates that
ACCEPTED MANUSCRIPT pentacene can be as a new member to be added to the HTL family for inverted planar PSCs.
Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant
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Nos.11274256, 11774293), Program for Innovation Team Building at Institutions of Higher Education in Chongqing (CXTDX201601011), Fundamental Research Funds for the Central Universities (XDJK2017A002), Natural Science Foundation of Technology Department (QKHJZ-LKZS[2014]10, and Key Laboratory and Scientific Research Foundation of Zunyi City
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(SSKH[2015]55).
References
G. Xing, N. Mathews, S. Sun, S.S. Lim, Y.M. Lam, M. Grätzel, S. Mhaisalkar, T.C. Sum, Science 342 (2013) 344-347.
[2]
M AN U
[1]
G.W. Ji, G.H.J. Zheng, B. Zhao, F. Song, X.N. Zhang, K.C. Shen, Y.G. Yang, Y.M. Xiong, X.Y. Gao, L. Cao and D.C. Qi, Phys. Chem. Chem. Phys. 19 (2017) 6546.
[3]
S.D. Stranks, G.E. Eperon, G. Grancini, C. Menelaou, M.J. Alcocer, T. Leijtens, L.M. Herz, A. Petrozza, H.J. Snaith, Science 342 (2013) 341-344.
[4]
D. Bi, W. Tress, M.I. Dar, P. Gao, J. Luo, C. Renevier, K. Schenk, A. Abate, F. Giordano, J.P. Correa Baena,
1501170. [5]
TE D
J.D. Decoppet, S.M. Zakeeruddin, M.K. Nazeeruddin, M. Grätzel and A. Hagfeldt, Sci. Adv. 2 (2016)
Y.Q. Yao, G. Wang, F. Wu, D.B. Liu, C.Y. Lin, X. Rao, R. Wu, G.D. Zhou, Q.L. Song, RSC Adv. 7 (2017) 42973-42978.
A. Kojima, K. Teshima, Y. Shirai and T. Miyasaka, J. Am. Chem. Soc. 131 (2009) 6050-6051.
[7]
J.H. Im, I.H. Jang, N. Pellet, M. Grätzel and N.G. Park, Nat. Mater. 13 (2014) 897-903.
[8]
D.X. Liu and Y.S. Liu, J. Semicond. 38 (2017) 011005.
[9]
D. Forgács, M. Sessolo, H.J. Bolink, J. Mater. Chem. A 3 (2015) 14121-14125.
EP
[6]
AC C
[10] M. Liu, M.B. Johnston, H.J. Snaith, Nature 501 (2013) 395-398. [11] H. Zhou, Q. Chen, G. Li, S. Luo, T. Song, H.S. Duan, Z. Hong, J. You, Y. Liu and Y. Yang, Science 345 (2014) 542-546.
[12] P. Schulz, E.E.S. Kirmayer, G. Hodes, D. Cahenb and A. Kahn, Energ. Environ. Sci. 7 (2014) 1377. [13] S. Ryu, J.H. Noh, N.J. Jeon, Y.C. Kim, W.S. Yang, J. Seo and S.I. Seok, Energ. Environ. Sci. 7 (2014) 2614-2618. [14] J.Y. Jeng, K.C. Chen, T.Y. Chiang, P.Y. Lin, T.D. Tsai, Y.C. Chang, T.F. Guo, P. Chen, T.C. Wen, Y.J. Hsu, Adv. Mater. 26 (2014) 4107. [15] S.F. Voelker, S. Collavini and J.L. Delgado, ChemSusChem 8 (2015) 3012-3028. [16] M. Jørgensen, K. Norrman, F.C. Krebs, Sol. Energ. Mat. Sol. C. 92 (2008) 686. [17] C.J. Huang, J.C. Ke, W.R. Chen, T.H. Meen, C.F. Yang, Sol. Energ. Mat. Sol. C. 95 (2011) 3460-3464. [18] P.H. Huang, C.J. Huang, K.L. Chen, J.C. Ke, Y.H. Wang and C.C. Kang, J. Nanomater. (2014) 741761. [19] H.A. Abbas, R. Kottokkaran, B. Ganapathy, M. Samiee, L. Zhang, A. Kitahara, M. Noack and V.L. Dalal,
ACCEPTED MANUSCRIPT APL Mater. 3 (2015) 16105. [20] W.H. Nguyen, C.D. Bailie, E.L. Unger, M.D. McGehee, J. Am.Chem. Soc. 136 (2014) 10996. [21] D.W. Zhao, M. Sexton, H-Y. Park, G. Baure, J.C. Nino, and F. So, Adv. Energy Mater. 5 (2015) 1401855. [22] S.K. Park, T.N. Jackson, J.E. Anthony and D.A. Mourey, Appl. Phys. Lett. 91 (2007) 063514. [23] C.D. Sheraw, T.N. Jackson, D.L. Eaton and J.E. Anthony, Adv. Mater. 15 (2003) 2009-2011. [24] S. Lee, D. Hwang, S.I. Jung and D. Kim, J. Phys. Chem. Lett. 8 (2017) 884−888. [25] S. Kazim, F.J. Ramos, P. Gao, M.K. Nazeeruddin, M. Grätzel and S. Ahmad, Energ. Environ. Sci. 8 (2015)
RI PT
1816-1823.
[26] G.W. Ji, B. Zhao, F. Song, G.H.J. Zheng, X.N. Zhang, K.C. Shen, Y.G. Yang, S. Chen, X.Y. Gao, Appl. Surf. Sci. 393 (2017) 417-421.
[27] Y. Xiao, G. Han, Y. Li, M. Li and J. Wu, J. Mater. Chem. A 2 (2014) 16856-16862.
[28] G. Wang, D.B. Liu, J. Xiang, D.C. Zhou, K. Alameh, B.F. Ding and Q.L. Song, RSC Adv. 6 (2016)
SC
43299-43303.
[29] F.Y. Jiang, Y.G. Rong, H.W. Liu, T.F. Liu, L. Mao, W. Meng, F. Qin, Y.Y. Jiang, B.W. Luo, S.X. Xiong, J.H. Tong, Y. Liu, Z.F. Li, H.W. Han and Y.H. Zhou, Adv. Funct. Mater. 26 (2016) 8119–8127.
M AN U
[30] S.R. Raga, M-C. Jung, M.V. Lee, M.R. Leyden, Y. Kato and Y. Qi, Chem. Mater. 27 (2015) 1597-1603. [31] J. You, Y. Yang, Z. Hong, T.B. Song, L. Meng, Y. Liu, C. Jiang, H. Zhou, W.H. Chang, G. Li and Y. Yang, Appl. Phys. Lett. 105 (2014) 183902.
[32] T. Leijtens, S.D. Stranks, G.E. Eperon, R. Lindblad, E.M.J. Johansson, I.J. McPherson, H. Rensmo, J.M. Ball, M.M. Lee, H.J. Snaith, ACS Nano 8 (2014) 7147.
[33] Q. Wang, Y. Shao, Q. Dong, Z. Xiao, Y. Yuan, J. Huang, Energ. Environ. Sci. 7 (2014) 2359. [34] G.D. Zhou, S.K. Duan, P. Li, B. Sun, B. Wu, Y.Q. Yao, X.D. Yang, J.J. Han, J.G. Wu, G. Wang, L.P. Liao,
(2018) 1700567.
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C.Y. Lin, W. Hu, C.Y. Xu, D.B. Liu, T. Chen, L.J. Chen, A.K. Zhou and Q.L. Song, Adv. Electron. Mater.
[35] G.D. Zhou, B. Sun, Y. Yao, H. Zhang, A. Zhou, K. Alameh, B. Ding and Q.L. Song, Appl. Phys. Lett. 109 (2016) 143904.
[36] M.M. Lee, J. Teuscher, T. Miyasaka, T.N. Murakami and H.J. Snaith, Science 338 (2012) 643-647.
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[37] G.D. Zhou, L.H. Xiao, S.J. Zhang, B. Wu, X. Liu, A.K. Zhou, J. Alloys. Compd. 722 (2017) 753-759. [38] G.D. Zhou, B. Sun, A. Zhou, B. Wu, Curr. Appl. Phys. 17 (2017) 235-239. [39] D.B. Liu, G. Wang, F. Wu, R. Wu, T. Chen, B.F. Ding, Q.L. Song, Org. Electron. 43 (2017) 189-195.
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[40] G.E. Eperon, V.M. Burlakov, P. Docampo, A. Goriely and H.J. Snaith, Adv. Funct. Mater. 24 (2014) 151-157.
[41] [40] G.D. Zhou, Y.Q. Yao, Z.S. Lu, X.D. Yang, J.J. Han, G. Wang, X. Rao, P. Li, Q. Liu, Q.L. Song, Nanotechnology 28 (2017) 425202.
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Highlights 1． A cost-effective and efficient organic semiconductor pentacene was developed as a hole transport layer (HTL) material for perovskite solar cells.
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2． The vacuum deposited pentacene based device exhibits a comparable performance with the classical PEDOT:PSS based device.
3． The high-quality perovskite film and the optimized energy-level alignment with downward
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band bending facilitate efficient charge extraction at perovskite/pentacene interface.
4． This study confirmed that pentacene could experimentally serve as a viable HTL candidate for
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efficient perovskite-based solar cells.
S1567-1739(18)30152-4
DOI:
10.1016/j.cap.2018.05.022
Reference:
CAP 4763
To appear in:
Current Applied Physics
Received Date: 10 April 2018 Revised Date:
22 May 2018
Accepted Date: 23 May 2018
Please cite this article as: X. Yang, G. Wang, D. Liu, Y. Yao, G. Zhou, P. Li, B. Wu, X. Rao, Q. Song, Pentacene as a hole transport material for high performance planar perovskite solar cells, Current Applied Physics (2018), doi: 10.1016/j.cap.2018.05.022. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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A cost-effective and efficient organic semiconductor pentacene was developed as a hole transport layer material to substitute classical PEDOT:PSS for planar perovskite solar cells. The pentacene based device exhibits the comparable performance to the PEDOT:PSS based device, which is mainly attributed to the high-efficiency charge extraction derived from the high-quality perovskite film and favorable energy-level alignment together with a desired downward band bending.
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Pentacene as a hole transport material for high performance planar perovskite solar cells Xiude Yang a, b,c #, Gang Wang a,b #, Debei Liu a,b, Yanqing Yao a,b, Guangdong Zhou a,b, Ping Li c, Bo Wu c, Xi Rao a,b, Qunliang Song a,b * Institute for Clean Energy & Advanced Materials (ICEAM), Southwest University, Chongqing 400715, P. R. China
b.
Chongqing Key Laboratory for Advanced Materials and Technologies of Clean Energy, Chongqing 400715, P. R. China
c.
School of Physics and Electronic science, Zunyi Normal College, Zunyi 563002, P. R. China Xiude Yang and Gang Wang contributed equally to this work
＃
*
E-mail: [email protected]
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a.
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Abstract：A cost-effective and efficient organic semiconductor pentacene was developed as a hole transport layer (HTL) material to replace classical PEDOT:PSS for planar perovskite solar cells
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(PSCs). As expected, the pentacene based device exhibits power conversion efficiency (PCE) of 15.90% (Jsc of 19.44 mA/cm2, Voc of 1.07 V, and FF of 77%), comparable to the PEDOT:PSS based device (PCE of 15.65%, Jsc of 18.78 mA/cm2, Voc of 1.07 V, and FF of 77%) under the same experimental conditions. The excellent performance of vacuum deposited pentacene is
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mainly attributed to the high efficient charge extraction and transfer in device due to the high-quality perovskite film grown on the top of pentacene substrate and a favorable energy-level alignment together with a desired downward band bending formed at the perovskite/pentacene interface. Our research has confirmed that pentacene could be served as a promising HTL material
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to achieve effective and potentially economical planar type PSCs.
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Keywords: pentacene; hole transport layer; perovskite solar cells
1. Introduction
Recently, organic-inorganic hybrid perovskite compounds considered as a class of
approximatively ideal light absorbers have been extensively focused and studied on solar cells. They have unique features such as the high absorption coefficient across visible spectrum, low trap-state density, long carrier diffusion length and lifetime. [1-3] Just over the past several years, perovskite solar cells (PSCs) with multiple architectures have been developed rapidly and the power conversion efficiency (PCE) has already exceeded 20% [4,5] since perovskite was firstly
ACCEPTED MANUSCRIPT reported for dye-sensitized solar cell with a PCE of mere 3.8%, [6] showing vigorous development trend
and
potential
application
prospect.
(N,N’-di-p-methoxyphenylamine)-9,9’-spirobifluorene
Especially,
(spiro-OMETAD)
2,2’,7,7’-tetrakis was
applied
for
preparing the all-solid PSC, which represented a significant breakthrough in device's development
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from original mesoporous structure to newly planar structure. [7] Currently, a large number of researches have indicated that the PCE of perovskite based solar cells is not only determined by the fabrication processes and conditions, but also considerably depends on superior hole transport layer (HTL) and electron transport layer (ETL) materials for
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efficient carrier extraction in devices. [8] Correspondingly, intensive efforts have been dedicated to exploit high-performance PSCs via seeking more better materials as efficient ETL and HTL. To
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date, there are mainly two prototypes of planar architectures in PSC community: conventional n-i-p structure with transparent cathode/ETL (n)/perovskite (i)/HTL (p)/anode [9] and so called “inverted” p-i-n structure with transparent anode/HTL (p)/perovskite (i)/ETL (n)/cathode [10]. As for n-i-p type PSCs, in previous studies, many HTL materials such as spiro-OMETAD,
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polytriarylamine (PTAA) and NiO, which were sandwiched between anode and perovskite, increased PCE significantly. [11-14] Similarly, for inverted p-i-n type PSCs, inspired by the organic solar cells (OSCs), some excellent photoelectric materials formerly employed in OSCs also served as HTLs for PSCs to distinctly promote the device efficiency. For instance,
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Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) (PEDOT:PSS) was commonly utilized as a HTL and has obtained favorable device performance. [15,16] As such, high efficient CuPc,
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P3HT and rubrene HTL based PSCs were demonstrated sequentially by the following literatures. [2, 17-19] Among all of HTL materials mentioned above, although both the use of spiro-OMeTAD in n-i-p structure and PEDOT:PSS in p-i-n structure are proved to be most successful, their own issues are also destructive to develop PSC devices. Spiro-OMeTAD requires a complex and strict doping strategy, which increases the overall cost and meanwhile induces the device instability and unrepeatability. [20] While PEDOT:PSS would corrode the indium-tin oxide (ITO) electrode, causing migration of indium into PEDOT:PSS, and its hygroscopic nature tends to degrade the resultant devices owing to the water uptake. [21] Accordingly, searching more stable and
ACCEPTED MANUSCRIPT economically viable HTL materials for PSCs to promote effective exciton dissociation/charge extraction is still a very important task. Pentacene with a molecular structure shown in Fig. 1a is a superior p-type semiconductor, which was vastly employed in organic field effect transistors [22,23] and OSCs [17,18] in the past.
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In recent reports, its derivatives were verified as high effective HTLs for fabricating PSCs. [24,25] Particularly, Gao et al. [26] have found that the pentacene/CH3NH3PbI3 interface could form a suitable energy-level diagram to efficiently facilitate charge transportation, thereout forecasting that pentacene is an unquestionably matched HTL material for the above two type of PSCs.
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However, the related experiment investigation on device performance to pentacene HTL based PSCs hasn't been reported so far.
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In this work, by adopting the physical vapor deposition (PVD) system, a thin pentacene HTL for PSC has been deposited on ITO to take place of classical PEDOT:PSS HTL in the reference device with a planar p-i-n structure of ITO/PEDOT:PSS/perovskite/fullerene derivatives ([6,6]-phenyl-c61-butyric
acid
methyl
ester
(PCBM)/C60
(10
nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (4 nm)/Ag. A champion PCE of
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15.90% with a best short-circuit current (Jsc) of 19.44 mA/cm2 is acquired in the device with pentacene HTL, whose performance is almost the same as the reference device with PEDOT:PSS HTL (PCE of 15.65% and Jsc of 18.89 mA/cm2) under the same fabrication conditions.
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Additionally, both the high-quality perovskite film deposited on pentacene layer and the optimized energy-level alignment formed at the perovskite/pentacene interface attested that pentacene could
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experimentally serve as a viable HTL candidate for efficient perovskite-based solar cells.
Experiment
2.1 Materials
N,N-dimethylformide (DMF), dimethyl sulfoxide (DMSO), chlorobenzene (CB) and
pentacene were bought from Sigma-Aldrich. PEDOT:PSS, methyl ammonium iodide (MAI), lead iodide (PbI2), lead chloride (PbCl2), PCBM and BCP were purchased from Xi 'an Polymer Light Technology Corp (China).The perovskite precursor solution was prepared with 0.14 M PbCl2, 1.26 M PbI2 and 1.4 M MAI dissolved in a co-solvent of DMSO and DMF (vol. ratio = 1: 9) in a glove
ACCEPTED MANUSCRIPT box and stirred overnight under room temperature. 2.2 Device fabrication The schematic architecture of PSC and corresponding energy level are illustrated in Figs.1b and c, respectively. The preparation process of PSCs can be divided into three parts: substrate
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cleaning, function layers and electrode growth. The details are described as follows:
Fig.1 (a) The molecule structure of pentacene, (b) the architecture of the PSCs with pentacene HTL, and (c) the corresponding energy level diagram of devices.
Substrate cleaning: ITO substrate was sequentially cleaned in an ultrasonic bath with a detergent of Decon 90, acetone, deionized water and ethanol, then dried under N2 stream. The growth of functional layers: A thin pentacene layer (30 nm) was deposited on ITO by thermal evaporation under high-vacuum, which was monitored by a quartz crystal. Afterwards, the filtered perovskite precursor was grown on pentacene by one-step spin-coating method at 1000 rpm for 3 s and 4000 rpm for 20 s, then 200 µL CB dropped quickly in the second step, and then
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The growth of electrode: Finally, a 10 nm C60, a 4 nm BCP and a 100 nm Ag electrode were sequentially deposited through a shadow mask in the same way as pentacene. The active cell area was 0.09 cm2. 2.3 Characterization
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The morphology and cross-section of the as-prepared perovskite films deposited on PEDOT:PSS or pentacene were observed by using a field-emission scanning electron microscopy
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(SEM, JSM-6700F). Their corresponding crystal structures were examined by an X-ray diffraction system (Shimadzu XRD-7000). And the UV-Vis absorption measurements were carried out using Shimadzu UV-2550 spectrometer.
The current density-voltage (J–V) characteristics for the developed PSCs were measured by
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Keithley 2400 source meter in conjunction with 100 mW/cm2 (AM 1.5 G) simulated sunlight from a solar simulator (Newport 94043A). During the measurement, reverse scan (from 1.2 to -1.2 V) and forward scan (from -1.2 to 1.2 V) were performed with a voltage step of 10 mV and 0 ms delay time. The external quantum efficiency (EQE) of devices was calculated from photocurrent
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generated from the modulated monochromatic light by a lock-in amplifier (SR-830). Both the J–V and EQE characteristics were tested in the N2-filled glove box.
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Transient photovoltage (TPV) tests of the as-prepared cells were performed directly in series
with an oscilloscope (Agilent DSO-X 3102A). During the measurements, the input impedance of oscilloscope was switched to 1 MΩ and the 532 nm pulsed laser was used as the excitation light source.
3. Results and discussion 3.1 XRD and SEM characterization The XRD patterns of perovskite films deposited on pentacene or PEDOT:PSS are shown in Fig. 2. The main diffraction peaks at 14.14°, 28.48° and 31.92°, which respectively corresponds to
ACCEPTED MANUSCRIPT the (110), (220) and (310) lattice plane of MAPbI3 crystal structure are observed, evidencing the formation of typical tetragonal phase in perovskite films as previously reported. [27,28] It is worth noting that although very weaker PbI2 diffraction peak could be found around 12.5°, the residual PbI2 would passivate perovskite grain boundaries to boost the VOC of MAPbI3 devices, which was
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demonstrated in previous report [29]. And, none of MAPbCl3 diffraction peaks is discovered since most chloride ions escape from NH3CH3Cl during annealing process. [28,30] Furthermore, the intensity of diffraction peaks of (110) and (220) faces on pentacene is slightly lower than that on PEDOT:PSS, reflecting enhanced crystallinity of perovskite film on PEDOT:PSS. This is likely
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due to the faster crystal growth of film during annealing stage, which is facilitated as a result of the moisture absorbed by PEDOT:PSS during spin-coated process in air. [31]
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Figs. 3a,b display the SEM images of perovskite films deposited on pentacene and PEDOT:PSS, respectively. Excitedly, the perovskite film on pentacene shows a larger average grain size than that on PEDOT:PSS, which is more beneficial for charge carrier transportation. This is because the smaller grain size leads to a larger boundary density, and consequently more
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defect states generated at grain boundaries would negatively affect carrier transfer, eventually reducing the device performance due to trap filling of the photo-induced electrons and an accumulation of holes. [32-35] Besides, the perovskite film on pentacene also exhibits the relatively more smoother surface and higher coverage compared with film on PEDOT:PSS. Also,
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in cross-section SEM images (see Fig.S1 in supporting information), a ~450 nm perovskite layer over a ~30 nm PEDOT:PSS HTL or ~30 nm pentacene HTL are clearly observed. Hence, we
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conclude that the formation of a high-quality perovskite film on pentacene promotes an efficient charge extraction.
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Fig.2 The XRD patterns of perovskite films deposited on pentacene and PEDOT:PSS, respectively.
Fig.3 The SEM images of perovskite films deposited respectively on (a) pentacene, and (b) PEDOT:PSS.
3.2 TPV measurements of PSCs To examine the effectivity of charge extraction in devices, TPV tests were used to assess the
lifetime of the free carriers in the two different PSCs. The longer the lifetime of the free carriers is, the longer the TPV decay-time is. Fig. 4 displays the normalized TPV in the PSCs with PEDOT:PSS HTL and pentacene HTL. The pentacene based device shows a slight longer photovoltage decay (~1.13 ms) to the PEDOT:PSS based reference device (~0.88 ms). The results indicate that they have an approximately equal lifetime of charge carriers, which proves the
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PEDOT:PSS device.
Fig.4 TPV measurements of PSCs with PEDOT:PSS HTL or pentacene HTL.
3.3 Photovoltaic performance of PSCs
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To further verify the performance and feasibility of pentacene as an efficient HTL in p-i-n type PSCs, the J-V characteristics of two devices with different HTLs are shown in Fig. 5a, and their corresponding photovoltaic parameters are listed in Table 1. The reference device with PEDOT:PSS HTL yields a PCE of 15.65% with Jsc, open circuit voltage (Voc) and fill factor (FF)
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of 18.78 mA/cm2, 1.07 V and 77%, respectively, which shows consistent performance similar to the results in previous studies. [15,16] To our surprise, under the same experimental conditions,
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the device with pentacene HTL also exhibits a laudable performance with PCE of 15.90%, Jsc of 19.44 mA/cm2, Voc of 1.07 V and FF of 77%, of which all device parameters are almost equal to the reference device with PEDOT:PSS HTL. The EQE spectrum measurements of two different HTL devices were conducted to confirm the Jsc, as presented in Fig. 5b. The calculated integral current densities of the devices with pentacene HTL and with PEDOT:PSS HTL (see Fig.S2 in supporting information) are 19.22 mA/cm2 and 19.00 mA/cm2, respectively, consisting with the aforementioned J-V measurement results. Note that, though the buffer layers are different, the UV-Vis light absorbance of the perovskite films are similar, as shown in Fig.S3 (supporting
ACCEPTED MANUSCRIPT information). In addition, Figs. 5c, d show the forward and reverse J-V curves of PSCs with pentacene and with PEDOT:PSS HTL, respectively. Fortunately, there is no obvious hysteresis emerging in the two devices, suggesting that both of them own good balanced electron and hole flux as well as less surface traps. [2, 36-38] Furthermore, the stability tests for two different HTL
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devices were carried out for about 200 s inside a N2-filled glove box. The test results show that both PCEs have a very slight decay at the maximum power point, as shown in Fig.S4 (supporting information). Apparently, pentacene could contribute the same effort as PEDOT:PSS for inverted PSCs. Therefore, there is no doubt that pentacene can be adopted as a practicable HTL candidate
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to substitute PEDOT:PSS for fabricating efficient inverted perovskite based solar cells.
Fig. 5 (a) J-V curves of devices with pentacene HTL and with PEDOT:PSS HTL, respectively. (b) EQE spectra of the two corresponding devices. The forward and reverse J-V curves of device (c) with pentacene HTL, and (d) with PEDOT:PSS HTL. Table 1. Photovoltaic performance of the devices with pentacene HTL and with PEDOT:PSS HTL. HTL
Scan direction
Voc (V)
Jsc (mA/cm2)
FF (%)
PCE (%)
PEDOT:PSS
Forward
1.07
18.89
77
15.65
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pentacene
Reverse
1.07
18.78
77
15.50
Forward
1.07
19.22
77
15.85
Reverse
1.07
19.44
76
15.90
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By comprehensive comparison and analysis with PEDOT:PSS HTL device, the outstanding performance of device with pentacene HTL maybe mainly ascribed to two aspect factors as follows:
On one hand, as previous studies have reported that there is a positive correlation between the
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device performance and the quality of perovskite films in device, [39,40] thus we deduce that the high performance of pentacene HTL device should partly come from the formations of a good
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tetragonal phase crystallinity and a high-quality morphology of perovskite film, as evidenced from XRD and SEM characterization displayed in Figs. 3a,b. Especially, the larger grain size, better coverage and higher flatness of perovskite film grown on pentacene result in less grain boundaries and trap state density, [32,33] which is favor of efficient charge extraction and transportion in
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device, consequently a slight higher PCE and Jsc are achieved with respect to the PEDOT:PSS HTL device. The effectiveness of charge-extraction is also revealed by the aforementioned TPV measurements.
More importantly, the matching energy-level alignment and the effect of downward band
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bending formed at perovskite/pentacene interface are also responsible for the expected performance of device with pentacene HTL, which is supported by XPS and UPS measurement
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results from previous research. [26] Firstly, from the energy-level diagram of device (in Fig.1c), it clearly shows that the HOMO level of pentacene is energetically favorable with regards to the valence band of perovskite in device, merely 0.2 eV energy difference in comparison with PEDOT:PSS of -5.2 eV. Moreover, on basis of the report from Ref.26, it is very interesting to note that a downward band bending together with an interfacial dipole at the pentacene side is observed due to the charge exchange at interface. [2, 41] As a consequence, a rather low HOMO-VBM offset ∆Ev and a large LUMO-CBM offset ∆Ec at the perovskite/pentacene interface are created, which can be depicted in Fig.6. Eventually, this desirable energy level alignment and downward
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is worth being exploited in inverted p-i-n planar PSCs.
Fig.6 The energy level diagram at the perovskite CH3NH3PbI3/pentacene interface
4. Conclusion
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In summary, we have developed a cost-effective and efficient organic semiconductor pentacene as a HTL material for inverted PSCs without the usage of PEDOT:PSS, additional
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dopants/additives as well as high temperature sintering. Remarkably, the admirable performance of pentacene based device is comparable to the classical PEDOT:PSS based device under the same experiment conditions. This is mainly attributed to the high efficient charge extraction and transfer derived from the high-quality perovskite film grown on top of the pentacene with an appropriate grain size, good coverage and flatness, and a favorable energy-level alignment with desired downward band bending formed at the perovskite/pentacene interface. In such a device, a champion efficiency as high as 15.90% and the highest Jsc of 19.44 mA/cm2 are obtained. All these results convincingly demonstrate that pentacene can be served as a promising HTL material to achieve efficient and economical thin film photovoltaic devices. This study also indicates that
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Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant
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Nos.11274256, 11774293), Program for Innovation Team Building at Institutions of Higher Education in Chongqing (CXTDX201601011), Fundamental Research Funds for the Central Universities (XDJK2017A002), Natural Science Foundation of Technology Department (QKHJZ-LKZS[2014]10, and Key Laboratory and Scientific Research Foundation of Zunyi City
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(SSKH[2015]55).
References
G. Xing, N. Mathews, S. Sun, S.S. Lim, Y.M. Lam, M. Grätzel, S. Mhaisalkar, T.C. Sum, Science 342 (2013) 344-347.
[2]
M AN U
[1]
G.W. Ji, G.H.J. Zheng, B. Zhao, F. Song, X.N. Zhang, K.C. Shen, Y.G. Yang, Y.M. Xiong, X.Y. Gao, L. Cao and D.C. Qi, Phys. Chem. Chem. Phys. 19 (2017) 6546.
[3]
S.D. Stranks, G.E. Eperon, G. Grancini, C. Menelaou, M.J. Alcocer, T. Leijtens, L.M. Herz, A. Petrozza, H.J. Snaith, Science 342 (2013) 341-344.
[4]
D. Bi, W. Tress, M.I. Dar, P. Gao, J. Luo, C. Renevier, K. Schenk, A. Abate, F. Giordano, J.P. Correa Baena,
1501170. [5]
TE D
J.D. Decoppet, S.M. Zakeeruddin, M.K. Nazeeruddin, M. Grätzel and A. Hagfeldt, Sci. Adv. 2 (2016)
Y.Q. Yao, G. Wang, F. Wu, D.B. Liu, C.Y. Lin, X. Rao, R. Wu, G.D. Zhou, Q.L. Song, RSC Adv. 7 (2017) 42973-42978.
A. Kojima, K. Teshima, Y. Shirai and T. Miyasaka, J. Am. Chem. Soc. 131 (2009) 6050-6051.
[7]
J.H. Im, I.H. Jang, N. Pellet, M. Grätzel and N.G. Park, Nat. Mater. 13 (2014) 897-903.
[8]
D.X. Liu and Y.S. Liu, J. Semicond. 38 (2017) 011005.
[9]
D. Forgács, M. Sessolo, H.J. Bolink, J. Mater. Chem. A 3 (2015) 14121-14125.
EP
[6]
AC C
[10] M. Liu, M.B. Johnston, H.J. Snaith, Nature 501 (2013) 395-398. [11] H. Zhou, Q. Chen, G. Li, S. Luo, T. Song, H.S. Duan, Z. Hong, J. You, Y. Liu and Y. Yang, Science 345 (2014) 542-546.
[12] P. Schulz, E.E.S. Kirmayer, G. Hodes, D. Cahenb and A. Kahn, Energ. Environ. Sci. 7 (2014) 1377. [13] S. Ryu, J.H. Noh, N.J. Jeon, Y.C. Kim, W.S. Yang, J. Seo and S.I. Seok, Energ. Environ. Sci. 7 (2014) 2614-2618. [14] J.Y. Jeng, K.C. Chen, T.Y. Chiang, P.Y. Lin, T.D. Tsai, Y.C. Chang, T.F. Guo, P. Chen, T.C. Wen, Y.J. Hsu, Adv. Mater. 26 (2014) 4107. [15] S.F. Voelker, S. Collavini and J.L. Delgado, ChemSusChem 8 (2015) 3012-3028. [16] M. Jørgensen, K. Norrman, F.C. Krebs, Sol. Energ. Mat. Sol. C. 92 (2008) 686. [17] C.J. Huang, J.C. Ke, W.R. Chen, T.H. Meen, C.F. Yang, Sol. Energ. Mat. Sol. C. 95 (2011) 3460-3464. [18] P.H. Huang, C.J. Huang, K.L. Chen, J.C. Ke, Y.H. Wang and C.C. Kang, J. Nanomater. (2014) 741761. [19] H.A. Abbas, R. Kottokkaran, B. Ganapathy, M. Samiee, L. Zhang, A. Kitahara, M. Noack and V.L. Dalal,
ACCEPTED MANUSCRIPT APL Mater. 3 (2015) 16105. [20] W.H. Nguyen, C.D. Bailie, E.L. Unger, M.D. McGehee, J. Am.Chem. Soc. 136 (2014) 10996. [21] D.W. Zhao, M. Sexton, H-Y. Park, G. Baure, J.C. Nino, and F. So, Adv. Energy Mater. 5 (2015) 1401855. [22] S.K. Park, T.N. Jackson, J.E. Anthony and D.A. Mourey, Appl. Phys. Lett. 91 (2007) 063514. [23] C.D. Sheraw, T.N. Jackson, D.L. Eaton and J.E. Anthony, Adv. Mater. 15 (2003) 2009-2011. [24] S. Lee, D. Hwang, S.I. Jung and D. Kim, J. Phys. Chem. Lett. 8 (2017) 884−888. [25] S. Kazim, F.J. Ramos, P. Gao, M.K. Nazeeruddin, M. Grätzel and S. Ahmad, Energ. Environ. Sci. 8 (2015)
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1816-1823.
[26] G.W. Ji, B. Zhao, F. Song, G.H.J. Zheng, X.N. Zhang, K.C. Shen, Y.G. Yang, S. Chen, X.Y. Gao, Appl. Surf. Sci. 393 (2017) 417-421.
[27] Y. Xiao, G. Han, Y. Li, M. Li and J. Wu, J. Mater. Chem. A 2 (2014) 16856-16862.
[28] G. Wang, D.B. Liu, J. Xiang, D.C. Zhou, K. Alameh, B.F. Ding and Q.L. Song, RSC Adv. 6 (2016)
SC
43299-43303.
[29] F.Y. Jiang, Y.G. Rong, H.W. Liu, T.F. Liu, L. Mao, W. Meng, F. Qin, Y.Y. Jiang, B.W. Luo, S.X. Xiong, J.H. Tong, Y. Liu, Z.F. Li, H.W. Han and Y.H. Zhou, Adv. Funct. Mater. 26 (2016) 8119–8127.
M AN U
[30] S.R. Raga, M-C. Jung, M.V. Lee, M.R. Leyden, Y. Kato and Y. Qi, Chem. Mater. 27 (2015) 1597-1603. [31] J. You, Y. Yang, Z. Hong, T.B. Song, L. Meng, Y. Liu, C. Jiang, H. Zhou, W.H. Chang, G. Li and Y. Yang, Appl. Phys. Lett. 105 (2014) 183902.
[32] T. Leijtens, S.D. Stranks, G.E. Eperon, R. Lindblad, E.M.J. Johansson, I.J. McPherson, H. Rensmo, J.M. Ball, M.M. Lee, H.J. Snaith, ACS Nano 8 (2014) 7147.
[33] Q. Wang, Y. Shao, Q. Dong, Z. Xiao, Y. Yuan, J. Huang, Energ. Environ. Sci. 7 (2014) 2359. [34] G.D. Zhou, S.K. Duan, P. Li, B. Sun, B. Wu, Y.Q. Yao, X.D. Yang, J.J. Han, J.G. Wu, G. Wang, L.P. Liao,
(2018) 1700567.
TE D
C.Y. Lin, W. Hu, C.Y. Xu, D.B. Liu, T. Chen, L.J. Chen, A.K. Zhou and Q.L. Song, Adv. Electron. Mater.
[35] G.D. Zhou, B. Sun, Y. Yao, H. Zhang, A. Zhou, K. Alameh, B. Ding and Q.L. Song, Appl. Phys. Lett. 109 (2016) 143904.
[36] M.M. Lee, J. Teuscher, T. Miyasaka, T.N. Murakami and H.J. Snaith, Science 338 (2012) 643-647.
EP
[37] G.D. Zhou, L.H. Xiao, S.J. Zhang, B. Wu, X. Liu, A.K. Zhou, J. Alloys. Compd. 722 (2017) 753-759. [38] G.D. Zhou, B. Sun, A. Zhou, B. Wu, Curr. Appl. Phys. 17 (2017) 235-239. [39] D.B. Liu, G. Wang, F. Wu, R. Wu, T. Chen, B.F. Ding, Q.L. Song, Org. Electron. 43 (2017) 189-195.
AC C
[40] G.E. Eperon, V.M. Burlakov, P. Docampo, A. Goriely and H.J. Snaith, Adv. Funct. Mater. 24 (2014) 151-157.
[41] [40] G.D. Zhou, Y.Q. Yao, Z.S. Lu, X.D. Yang, J.J. Han, G. Wang, X. Rao, P. Li, Q. Liu, Q.L. Song, Nanotechnology 28 (2017) 425202.
ACCEPTED MANUSCRIPT
Highlights 1． A cost-effective and efficient organic semiconductor pentacene was developed as a hole transport layer (HTL) material for perovskite solar cells.
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2． The vacuum deposited pentacene based device exhibits a comparable performance with the classical PEDOT:PSS based device.
3． The high-quality perovskite film and the optimized energy-level alignment with downward
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band bending facilitate efficient charge extraction at perovskite/pentacene interface.
4． This study confirmed that pentacene could experimentally serve as a viable HTL candidate for
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efficient perovskite-based solar cells.