Spin-coating free fabrication for highly efficient perovskite solar cells

Solar Energy Materials and Solar Cells 168 (2017) 165–171

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Solar Energy Materials and Solar Cells journal homepage: www.elsevier.com/locate/solmat

Spin-coating free fabrication for highly efficient perovskite solar cells a,b

a,⁎

a

a

a

Jianghui Zheng , Meng Zhang , Cho Fai Jonathan Lau , Xiaofan Deng , Jincheol Kim , ⁎ Qingshan Maa, Chao Chenb, Martin A. Greena, Shujuan Huanga, Anita W.Y. Ho-Bailliea,

MARK

a Australian Centre for Advanced Photovoltaics (ACAP), School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney 2052, Australia b College of Energy, Xiamen University, Xiamen 361005, China

A R T I C L E I N F O

A B S T R A C T

Keywords: Spin-coating free Perovskite solar cell Blow-drying Scalable process

A spin-coating-free fabrication sequence has been developed for the fabrication of highly efficient organicinorganic halide perovskite solar cells (PSCs). A novel blow-drying method is demonstrated to be successful in depositing high quality mesoporous TiO2 (mp-TiO2), methylammonium lead halide (CH3NH3PbI3) perovskite and spiro-MeOTAD layers. When combined with compact TiO2 (c-TiO2) deposited by spray pyrolysis which is also a spin-coating-free process, a stabilized power conversion efficiency exceeding 17% can be achieved for the glass/FTO/c-TiO2/mp-TiO2/ CH3NH3PbI3/spiro-MeOTAD/Au device. This is the highest efficiency for PSCs fabricated without the use of spin-coating to our knowledge. This method provides a pathway towards a scalable process for fabricating high-performance, large area and reproducible PSCs.

1. Introduction Organic-inorganic halide perovskites solar cells (PSCs) have emerged as a promising photovoltaic technology [1] due to their excellent optical properties [2], ambi-polar charge transport, low material usage and low temperature requirement during fabrication, and high photovoltaic power conversion efficiency (PCE) over the past few years. The PCE of PSCs has improved rapidly from 3.8% in 2009 to the most recent independently certified record at 22.1% in 2016 [3–10]. However, PSCs are still facing challenges including scale-up, instability, use of expensive blocking or transport layers and precious metals as electrodes and reliance on lead for the high efficiency cells. Although the amount of lead is small, its presence in soluble form may be enough to cause health concerns for consumers of the product especially for rooftop or home system applications. The research community in the field PSCs area has been addressing these issues using various approaches [11–24]. A state of the art PSC cell [2–7] typically consists of compact TiO2 (c-TiO2) layer, mesoporous TiO2 (mp-TiO2) layer, perovskite layer, hole transport material (HTM) and metal electrode. In addition, spin-coating method is typically used for these state-of-the-art solar cells. However, spin-coating is not compatible with high-volume large area solar cell manufacturing [25]. In an attempt to eliminate spin-coating, several approaches have been developed for fabricating efficient large area perovskite active layer, such as vacuum flash-assisted solution process

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[26], spray deposition [27,28] and doctor-blading method [29]. In the previous work by Zhang (also co-author of this work) et al., they have successfully applied blow-drying method to obtain the a high quality perovskite layer in air. Although high-quality perovskite active layer can be achieved, the hole blocking or electron transport layer and the HTM are still fabricated by spin-coating [30]. A few studies have developed scalable deposition process free of spin coating for the multiple layers in PSCs. Hwang et al. have demonstrated cells with PCE at 11.96% using fully slot-die coating method in 2015 [31]. Mohamad et al. also reported cells with PCE can reach at 9.9% using all-spray-process for inverted PSC devices [25]. Most recently, Lee et al. demonstrated spin-coating-free inverted planar heterojunction PSCs fabricated with successive brush-painting with PCE at 9.08% [32]. Unfortunately, these approaches have not yet produced cells with high efficiency comparable to those by spin-coating. Here, we demonstrate a novel blow-drying method for fabricating the various layers in highly efficient PSCs with conventional structure: glass/ fluorine-tin-oxide (FTO)/c-TiO2/mp-TiO2/CH3NH3PbI3 (MAPbI3)/2,2′, 7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]−9,9′-spirobifluorene (spiroMeOTAD/Au). Devices that removed spin-coating from the fabrication sequence achieve better results than the spin-coated counterparts under the same condition in this work. The champion device has a PCE exceeding 17%, which is the highest efficiency for PSCs fabricated without the use of spin-coating to the best of our knowledge. This method features several advantages. 1) The fabrication of perovskite layer does not require anti-

Corresponding authors. E-mail addresses: [email protected] (M. Zhang), [email protected] (A.W.Y. Ho-Baillie).

http://dx.doi.org/10.1016/j.solmat.2017.04.029 Received 7 February 2017; Received in revised form 7 April 2017; Accepted 14 April 2017 0927-0248/ © 2017 Published by Elsevier B.V.


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2.3. Characterisations

solvent that is an additional component and a sacrificial component. 2) This method produces good quality and smooth layer as shall be discussed below. 3) The solution processing sequence is scalable which combines one spraying process with the other layers deposited by blow-drying. 4) The equipment specification for this method is simple.

The current density–voltage (J–V) measurements were performed using a solar cell I–V testing system from Abet Technologies, Inc. (using class AAA solar simulator) under an illumination power of 100 mW cm−2 with an 0.159 cm2 aperture and a scan rate of 30 mV s −1 from open-circuit voltage (VOC) to short-circuit current density (JSC) direction (1.1 to −0.1 V). The bias voltage for the stead-state measurements was chosen as the average of maximum power point (MPP) voltage of the J-V measurement. Top view and cross-sectional scanning electron microscopy (SEM) images were obtained using a field emission SEM (NanoSEM 230). The optical reflection and transmission spectra were measured using Perkin Elmer Lambda1050 UV/Vis/NIR spectrophotometer. X-ray diffraction (XRD) patterns were measured using a PANalytical Xpert Materials Research diffractometer system with a Cu Kα radiation source (λ=0.1541 nm) at 45 kV and 40 mA at 2theta 10–60° and scan speed 3° min−1. Photoluminescence (PL) imaging, fluorescence lifetime imaging microscopy (FLIM) and the PL decay traces were measured by Microtime200 microscope (Picoquant) using time correlated single photon counting (TCSPC) technique with excitation of 470 nm laser at 5 MHz repetition rate and detection through 760/40 nm band-pass filter. All measurements were undertaken at room temperature in ambient condition.

2. Experimental section 2.1. Precursor solutions c-TiO2 precursor solution was prepared by dissolving 0.15 M titanium diisopropoxide bis(acetylacetonate) solution (Sigma-Aldrich, 75 wt% in isopropanol alcohol) in isopropyl alcohol (IPA, SigmaAldrich). mp-TiO2 precursor solution was prepared by diluting Dyesol 18 NR-T paste with a 1:4 mass ratio in IPA. The MAPbI3 perovskite precursor solution was prepared similar to method reported elsewhere [33], by mixing 461 mg of PbI2 (Alfa Aesar), 159 mg of CH3NH3I (Dyesol), 78 mg of dimethyl sulfoxide (DMSO, Alfa Aesar) (molar ratio 1:1:1) with 600 mg of dimethylformamide (DMF, Sigma-Aldrich) solution at room temperature under stirring for 1 h. The spiro-MeOTAD was prepared by dissolving 72.3 mg (2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene) (spiro-MeOTAD) (Lumtec), 28.8 μL, 4-tert-butylpyridine (Sigma-Aldrich), 17.5 μL lithium bis(trifluoromethylsulfonyl)imide (Sigma-Aldrich) solution (520 mg/mL in acetonitrile (Sigma-Aldrich)) and 8 μL FK209-cobalt(III)-TFSI (Lumtec) solution (300 mg of FK209-cobalt(III)-TFSI in 1 mL of acetonitrile) in 1 mL chlorobenzene (Sigma-Aldrich).

3. Results and discussion In this work, PSCs with the conventional structure of glass/FTO/cTiO2/mp-TiO2/MAPbI3/spiro-MeOTAD/Au are fabricated using the sequence illustrated in Fig. 1. Firstly, c-TiO2 layer was deposited by spray pyrolysis on the pre-patterned FTO substrates, followed by deposition of mp-TiO2, MAPbI3 and spiro‐MeOTAD layers all achieved using blow-drying method. The blow-drying method involves the dropping of the precursor solution on the substrate followed by blowdrying by N2 gas. The blow-drying duration is different and is optimised for different layer in this work. For the mp-TiO2 and MAPbI3 layers a heat treatment is needed. More details can be found in the Experimental Section. Finally, Au layer was deposited by evaporation. For comparison, 6 process sequences are used for the fabrication of devices. In all of these sequences, the first layer, i.e., the hole blocking c-TiO2 layer, is deposited by spray deposition while the last layer, i.e., the gold electrode is deposited by thermal evaporation. The variations between the 6 sequences lie in the deposition method used for the mpTiO2, MAPbI3 and the spiro-MeOTAD layers as listed in Table 1. This allows the effect of applying the blow-drying method to each individual layer on cell performance to be investigated. A summary of the device performance is listed in Table 1 while the distribution of parameters including VOC, JSC, fill factor (FF) and PCE for each device type (Group 1–6) are shown in Fig. 2. Fig. 3 shows the J-V curve and steady-state current density and efficiency of the champion blow-dried device (Device 1) and spin-coated device (Device 2). The results clearly show that blow-dried devices (Group 1) achieved higher average VOC (1035 mV) than spin-coated devices (Group 2) (961 mV), as well as better JSC (21.7 mA/cm2 as opposed to 20.9 mA/cm2) and therefore better cell performance. To understand the reasons for the improvements, devices in Group 3, 4 and 5 that have only one layer blow-dried with other two layers spin-coated are compared with devices in Group 2 that have all three layers spin-coated. The J-V curve and steady-state current density and efficiency of champion PSCs in Groups 1 and 2 are shown in Fig. 3 while those in Groups 3–5 are shown Fig. S1. The details of the spin coating and blow drying methods used can be found in the Experimental Section. The results revealed that the blow-dried mp-TiO2 layer has no apparent advantage over spin-coated mp-TiO2 as there is no improvement in JSC, FF and efficiency in Group 3 devices compared to Group 2 devices. Also, there is a larger spread in VOC in Group 3 devices

2.2. Device fabrication Patterned FTO-coated glass (Pilkington, 7 Ω □−1, transmittance 80%) was cleaned by sonication in de-ionized water with 2% Hellmanex, de-ionized water, acetone and isopropanol for 20 min. After N2 blow-drying, the FTO substrate was finally treated with ultraviolet ozone (UVO) cleaner for 15 min. To form the c-TiO2 blocking layer for all devices, a solution of titanium diisopropoxide bis(acetylacetonate) in IPA was deposited on the clean substrates by spray pyrolysis at 450 °C and the substrate was subsequently annealed on a hot plate at 450 °C for 10 min. Before mp-TiO2 layer deposition, the substrates for all devices were treated with UVO cleaner for 10 min. For spin-coating mp-TiO2 layer, the mp-TiO2 layer was deposited by spin-coating the mp-TiO2 precursor on the c-TiO2 layer for 30 s at 5500 rpm. For blow-dried mp-TiO2 layer, the mp-TiO2 precursor is dropped onto the stationary substrate followed by N2 gas blows (0.5 s duration) 2–3 times using a N2 gun. For both spin coated and blow dried, mp-TiO2, the samples were then dried at 100 °C for 5 min followed by annealing at 500 °C for 30 min in air. Prior to deposition of MAPbI3 perovskite film, the samples were treated with UVO cleaner for 10 min and then transferred to a N2 filled glovebox. For comparison, the spin coated perovskite samples were deposited using the gas-assisted spin-coating method [34], which involves the spinning of MAPbI3 precursor solution at 4000 rpm for 25 s with dry N2 gas stream blown over the film for 10 s during spinning. For the blow-dried perovskite samples, the MAPbI3 precursor solution was dropped onto the stationary mp-TiO2 coated substrate and immediately blown by a dry N2 gas onto the surface vertically. Both the spin-coated and blow-dried samples were dried at 100 °C for 10 min after deposition to produce a dark brown dense MAPbI3 film. For the spin-coated HTM samples, the spiro‐MeOTAD precursor was deposited on MAPbI3 layer by spin-coating at 3000 rpm for the 30 s. For the blow-dried HTM samples, the spiro‐MeOTAD precursor was dropped on the stationary MAPbI3 coated substrate and immediately blown by N2 gas blows (0.5 s duration) 2–3 times using a N2 gun producing a smooth HTM layer. Finally, 100 nm of gold was thermally evaporated on spiro‐MeOTAD layer to form the back electrode for all types of perovskite devices. 166


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Fig. 1. Fabrication sequence for our PSC devices.

lower than the FTO/c-TiO2/spin-coated mp-TiO2 test structure due to the thicker blow-dried mp-TiO2 layer, see Fig. S2 for the transmittance of the test structures. This explains the significant JSC drop experienced by Group 3 devices. Interestingly, it appears that the blow-dried mpTiO2 is compatible to blow dried MAPbIS but not compatible to spincoated MAPbI3. A blow-dried mp-TiO2/MAPbI3 combination results in respectable RS and RSH (Group 1 devices) but a blow-dried mp-TiO2/ spin coated MAPbI3 combination results in the lowest RS, RSH and therefore lowest FF (Group 3 devices). This is likely to be due to the thicker and less porous mp-TiO2 resulting in greater difficulty for the MAPbI3 to infiltrate the blow-dried meso-porous layer if the MAPbI3 is deposited via spin coating. The XRD patterns (see Fig. S3) of blow-dried MAPbI3 layer and the spin-coated MAPbI3 layer on FTO substrate suggest that highly crystallized MAPbI3 layer can be obtained using both methods. However, the cross-sectional SEM images (Fig. 4) show that blow-dried MAPbI3

compared to Group 2 devices. On the other hand, the advantage of blow-dried MAPbI3 is seen in the improvements of all of the electrical parameters for Group 4 devices compared to Group 2 devices. Another encouraging result is the better performance of blow-dried spiroMeOTAD as evidenced in cell results with higher VOC in Group 5 devices compared to Group 2 devices. To physically characterise the quality of the layers between these devices, the cross-sectional SEM images were taken, see Fig. 4a and b. It can be seen that thicknesses of layers differ between those fabricated by blow-drying and those by spin coating, see Table 2. In particular, the thickness of mp-TiO2 deposited by blow-drying is thicker than that by spin-coating, while the MAPbI3 capping layer and the spiro-MeOTAD layer by blow-drying are thinner than the spin-coated counterparts. The thicker blow-dried mp-TiO2 layer compared to the spin-coated mp-TiO2 layer explains the drop in cell performance. In particular, the light transmittance of the FTO/c-TiO2/blow-dried mp-TiO2 test structure is

Table 1 Six different solution-processing sequences used for devices reported in this work. The photovoltaic performances of the champion devices are shown in bold while the average values with standard deviations are shown in the parentheses. Group

1

2

3

4

5

6

mp-TiO2 MAPbI3 spiro-MeOTAD VOC [mV]

Blow Blow Blow 1043 (1035 ± 23) 21.7 (21.0 ± 0.7) 2.1 (2.2 ± 0.3) 2772 (2633 ± 997) 76.9 (73.1 ± 4.0) 17.4 (16.5 ± 0.9) 17.1

Spin Spin Spin 952 (961 ± 14) 20.9 (20.3 ± 1.0) 1.8 (2.3 ± 0.5) 743 (693 ± 70) 78.4 (75.8 ± 2.6) 15.6 (14.7 ± 0.90) 15.1

Blow Spin Spin 977 (967 ± 36) 18.5 (17.7 ± 0.8) 3.2 (4.1 ± 1.0) 833 (720 ± 113) 72.7 (72.9 ± 4.0) 13.1 (12.5 ± 0.7) 12.1

Spin Blow Spin 1018 (1009 ± 30) 22.3 (21.3 ± 1.1) 2.2 (2.4 ± 0.3) 1901 (1371 ± 530) 77.6 (75.5 ± 2.1) 17.7 (16.1 ± 1.6) 16.6

Spin Spin Blow 1006 (1013 ± 18) 19.6 (19.7 ± 0.9) 2.2 (2.2 ± 0.2) 1658 (1352 ± 365) 77.9 (75.7 ± 2.3) 16.3 (15.2 ± 1.1) 15.5

Spin Blow Blow 1074 (1064 ± 38) 21.9 (21.2 ± 0.8) 2.2 (2.3 ± 0.3) 4950 (5338 ± 685) 77.9 (75.1 ± 3.2) 18.3 (17.0 ± 1.3) 18.1

JSC [mA/cm2] RS [Ω cm2] RSH [Ω cm2] FF [%] PCE [%] Steady-State Efficiency [%]

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Fig. 2. Distribution of (a) VOC, (b) JSC, (c) FF, (d) and PCE for 10 devices in each device category (Group 1 to Group 6). The highest value is a maximum value. The highest bar is the 75th percentile value. The middle bar is the median value. The square mark is for average. The lowest bar is the 25th percentile value. The lowest value is the minimum.

infiltrates the mp-TiO2 much better than the spin-coated MAPbI3. As a result, the devices with blow-dried MAPbI3 achieve consistently higher VOC and JSC than the spin-coated counterparts as seen in Group 4 devices vs Group 2 devices and in Group 6 devices vs Group 5 devices. Finally, a blow-dried spiro-MeOTAD layer has been shown to be more compact than the spin-coated spiro-MeOTAD layer, see Fig. 4. It is found that devices with blow-dried spiro-MeOTAD layer exhibit higher RSH than those with spin-coated spiro-MeOTAD, e.g., RSH-Device 2 2 5=1658 Ω cm compared to RSH-Device2=743 Ω cm , see Table 1. This suggests that the compact, smooth, pinhole-free blow-dried spiroMeOTAD layer reduces the number of shunting paths. Moreover, the spatial PL intensity and lifetime obtained by PL imaging microscopy as shown in Fig. 5 reveal lower intensity and radiative lifetime in FTO/ MAPbI3/blow-dried spiro-MeOTAD sample compared to FTO/MAPbI3/ spin-coated spiro-MeOTAD sample suggesting better hole extraction by blow-dried spiro-MeOTAD. The time resolved PL measurements on FTO/MAPbI3/blow-dried spiro-MeOTAD and FTO/MAPbI3/spin-coated spiro-MeOTAD samples were carried out and shown in Fig. S4. The PL decay curve can be well fitted using the bi-exponential function according to the following:

better perovskite/spiro-MeOTAD interface being formed when blowdrying is used to deposit the spiro-MeOTAD layer. This could be due to the pressure of the gas applied on the wet film during blow-drying resulting in a more intimate contact between the perovskite and HTM layers. It is found that the best sequence is to combine the advantage of spin-coated mp-TiO2 with blow-dried MAPbI3 and spiro-MeOTAD layers producing Group 6 devices with the highest efficiency at 18.3% and stabilized efficiency at 18.1%. Higher VOC (1074 mV as opposed to 1043 mV for Device 3) and equally highly JSC can be achieved using this sequence, see Table 1 and Fig. S5. Although blowdrying is not the most ideal scalable solution process for mp-TiO2, when it is used for MAPbI3 and spiro-MeOTAD layers, better cell performance is achieved. This work demonstrates high performance perovskite solar cells can be fabricated without of spin-coating. Future work will involve the development of spin-coating-free scalable process for mp-TiO2 that is highly porous for the infiltration of blow-dried perovskite, capped by blow-dried perovskite and spiro-MeOTAD layers.

⎛t⎞ ⎛t ⎞ I = A1 exp ⎜ ⎟ + A2 exp ⎜ ⎟ ⎝ τ1 ⎠ ⎝ τ2 ⎠

In summary, a novel solution-processing sequence that is spincoating-free and scalable for PSCs is demonstrated. The use of blowdrying for depositing high quality mesoporous TiO2, methyl-ammonium lead halide perovskite and spiro‐MeOTAD layers in conjunction with the use of spray pyrolysis for depositing compact TiO2 produce high efficiency perovskite solar cells with PCE exceeding 17%. The reasons for improvements are investigated in this work by systematically replacing each spin coating step with a blow-drying step. The results show that blow-dried MAPbI3 achieves better infiltration and more compact film with fewer pinholes. Spiro-MeOTAD deposited by blow-drying produces better perovskite/spiro‐MeOTAD interface with

4. Conclusions

(1)

where I is PL decay, τ1 is the fast component and τ2 is the slow component, A1 is weighting of τ2 , A2 is weighting of τ2 . The biexponential fitting results of PL decay traces of FTO/MAPbI3/blowdried spiro-MeOTAD and FTO/MAPbI3/spin-coated spiro-MeOTAD samples were calculated and summarized in Table 3 [35]. The result indicates that blow-dried spiro-MeOTAD sample features a shorter decay time (10.60 ns) than spin-coated spiro-MeOTAD samples (12.60 ns) which is consistent with the spatial PL results, suggesting a 168


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Fig. 3. (a) J-V curve and (b) steady-state current density and efficiency of the champion blow-dried device of Group 1 (Device 1). (c) J-V curve and (d) steady-state current density and efficiency of the champion spin-coated device of Group 2 (Device 2).

fewer shunting paths and better hole extraction. This blow drying method features several advantages. 1) The fabrication of perovskite layer does not require anti-solvent that is an additional component and a sacrificial component. 2) This method produces good quality and smooth layer. 3) The solution processing sequence is scalable which combines one spraying process for c-TiO2 with the other layers deposited by blow-drying. 4) The equipment specification for this method is simple.

Table 2 Thicknesses estimated by cross sectional SEM for layers deposited using different methods.

mp-TiO2 (nm) MAPbI3 (nm) spiro-MeOTAD (nm)

Device 1 (blow-dried)

Device 2 (spin-coated)

380 190 80

280 460 180

Fig. 4. SEM cross-sectional images of (a) Device 1 fabricated by blow-drying and (b) Device 2 fabricated by spin coating showing differences in layer thickness in the cell structure FTO/cTiO2/mp-TiO2/MAPbI3/spiro-MeOTAD/Au.

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Fig. 5. Photoluminescence images showing spatial intensity of (a) FTO/MAPbI3/blow-dried spiro‐MeOTAD sample and (b) FTO/MAPbI3/spin-coated spiro‐MeOTAD sample. Lifetime images (c) and (d) of the same (a) and (b) samples, respectively. The images were collected using a pulsed laser excitation at 470 nm and a bandpass filter (760/40 nm). Table 3 Bi-exponential fitting results of PL decay traces for FTO/MAPbI3/blow-dried spiro‐MeOTAD and FTO/MAPbI3/spin-coated spiro‐MeOTAD samples. Sample

A1

A2

τ1 [ns]

τ2 [ns]

τeff [ns]

FTO/MAPbI3/blow-dried spiroMeOTAD FTO/MAPbI3/spin-coated spiroMeOTAD

36.8%

63.2%

12.71

2.66

10.05

62.9%

37.1%

13.99

3.71

12.60

[3]

[4]

[5]

[6]

Acknowledgments

[7]

J. Zheng and M. Zhang contributed equally to this work. The Australian Centre for Advanced Photovoltaics (ACAP) encompasses the Australian-based activities of the Australia-US Institute for Advanced Photovoltaics (AUSIAPV) and is supported by the Australian Government through the Australian Renewable Energy Agency (ARENA). This project is also supported by ARENA via the project 2014 RND075. J. Zheng wishes to acknowledge the support from Chinese Scholarship Council (Grant No. 201506310059). Authors would like to thank Dr. Ning Song at UNSW for the XRD measurement. We thank the Electron Microscopy Unit and the BioMedical Imaging Facility at UNSW for the SEM and fluorescence imaging supports.

[8]

[9]

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Appendix A. Supporting information [13]

Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.solmat.2017.04.029.

[14]

References [15] [1] M.A. Green, A. Ho-Baillie, H.J. Snaith, The emergence of perovskite solar cells, Nat. Photonics 8 (2014) 506–514. [2] Y. Jiang, M.A. Green, R. Sheng, A. Ho-Baillie, Room temperature optical properties

[16]

170

of organic–inorganic lead halide perovskites, Sol. Energy Mater. Sol. Cells 137 (2015) 253–257. A. Kojima, K. Teshima, Y. Shirai, T. Miyasaka, Organometal halide perovskites as visible-light sensitizers for photovoltaic cells, J. Am. Chem. Soc. 131 (2009) 6050–6051. J. Burschka, N. Pellet, S.J. Moon, R. Humphry-Baker, P. Gao, M.K. Nazeeruddin, M. Grätzel, Sequential deposition as a route to high-performance perovskitesensitized solar cells, Nature 499 (2013) 316–319. N.J. Jeon, J.H. Noh, Y.C. Kim, W.S. Yang, S. Ryu, S.I. Seok, Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells, Nat. Mater. 13 (2014) 897–903. N.J. Jeon, J.H. Noh, W.S. Yang, Y.C. Kim, S. Ryu, J. Seo, S.I. Seok, Compositional engineering of perovskite materials for high-performance solar cells, Nature 517 (2015) 476–480. Y.C. Kim, N.J. Jeon, J.H. Noh, W.S. Yang, J. Seo, J.S. Yun, A. Ho-Baillie, S. Huang, M.A. Green, J. Seidel, T.K. Ahn, S.I. Seok, Beneficial effects of PbI2 incorporated in organo-lead halide perovskite solar cells, Adv. Energy Mater. 6 (2016) 1502104. W.S. Yang, J.H. Noh, N.J. Jeon, Y.C. Kim, S. Ryu, J. Seo, S.I. Seok, Highperformance photovoltaic perovskite layers fabricated through intramolecular exchange, Science 348 (2015) 1234–1237. D. Bi, C. Yi, J. Luo, J.D. Décoppet, F. Zhang, S.M. Zakeeruddin, X. Li, A. Hagfeldt, M. Grätzel, Polymer-templated nucleation and crystal growth of perovskite films for solar cells with efficiency greater than 21%, Nat. Energy 1 (2016) 16142. M.A. Green, K. Emery, Y. Hishikawa, W. Warta, E.D. Dunlop, D.H. Levi, A.W. Ho‐Baillie, Solar cell efficiency tables (version 49), Prog. Photo.: Res. Appl. 25 (2017) 3–13. S. Razza, F. Di Giacomo, F. Matteocci, L. Cina, A.L. Palma, S. Casaluci, P. Cameron, A. D′epifanio, S. Licoccia, A. Reale, Perovskite solar cells and large area modules (100 cm2) based on an air flow-assisted PbI2 blade coating deposition process, J. Power Sources 277 (2015) 286–291. W. da Silva, Trendy solar cells hit new world efficiency record, 〈http://newsroom. unsw.edu.au/news/science-tech/trendy-solar-cells-hit-new-world-efficiencyrecord〉. [Accessed 05 April 2017]. F. Bella, G. Griffini, J.P. Correa-Baena, G. Saracco, M. Grätzel, A. Hagfeldt, S. Turri, C. Gerbaldi, Improving efficiency and stability of perovskite solar cells with photocurable fluoropolymers, Science 234 (2016) 203–206. M. Saliba, T. Matsui, K. Domanski, J.Y. Seo, A. Ummadisingu, S.M. Zakeeruddin, J.P. Correa-Baena, W.R. Tress, A. Abate, A. Hagfeldt, Incorporation of rubidium cations into perovskite solar cells improves photovoltaic performance, Science 354 (2016) 206–209. M. Zhang, J.S. Yun, Q. Ma, J. Zheng, C.F.J. Lau, X. Deng, J. Kim, D. Kim, J. Seidel, M.A. Green, S. Huang, A.W.Y. Ho-Baillie, High-efficiency rubidium-incorporated perovskite solar cells by gas quenching, ACS Energy Lett. 2 (2017) 438–444. I.C. Smith, E.T. Hoke, D. Solis‐Ibarra, M.D. McGehee, H.I. Karunadasa, A layered


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[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

hybrid perovskite solar‐cell absorber with enhanced moisture stability, Angew. Chem. 126 (2014) 11414–11417. H. Tsai, W. Nie, J.C. Blancon, C.C. Stoumpos, R. Asadpour, B. Harutyunyan, A.J. Neukirch, R. Verduzco, J.J. Crochet, S. Tretiak, High-efficiency two-dimensional Ruddlesden–Popper perovskite solar cells, Nature 536 (2016) 312–316. J. Kim, N. Park, J.S. Yun, S. Huang, M.A. Green, A.W. Ho-Baillie, An effective method of predicting perovskite solar cell lifetime–case study on planar CH3NH3PbI3 and HC(NH2)2PbI3 perovskite solar cells and hole transfer materials of spiro‐OMeTAD and PTAA, Sol. Energy Mater. Sol. Cells 162 (2017) 41–46. A. Mei, X. Li, L. Liu, Z. Ku, T. Liu, Y. Rong, M. Xu, M. Hu, J. Chen, Y. Yang, A holeconductor–free, fully printable mesoscopic perovskite solar cell with high stability, Science 345 (2014) 295–298. Y. Xiao, N. Cheng, K.K. Kondamareddy, C. Wang, P. Liu, S. Guo, X.Z. Zhao, W-doped TiO2 mesoporous electron transport layer for efficient hole transport material free perovskite solar cells employing carbon counter electrodes, J. Power Sources 342 (2017) 489–494. X. Jiang, Z. Yu, Y. Zhang, J. Lai, J. Li, G.G. Gurzadyan, X. Yang, L. Sun, Highperformance regular perovskite solar cells employing low-cost poly(ethylenedioxythiophene) as a hole-transporting material, Sci. Rep. 7 (2017) 42564. N.K. Noel, S.D. Stranks, A. Abate, C. Wehrenfennig, S. Guarnera, A.A. Haghighirad, A. Sadhanala, G.E. Eperon, S.K. Pathak, M.B. Johnston, Lead-free organic–inorganic tin halide perovskites for photovoltaic applications, Energy Environ. Sci. 7 (2014) 3061–3068. M. Zhang, M. Lyu, J.H. Yun, M. Noori, X. Zhou, N.A. Cooling, Q. Wang, H. Yu, P.C. Dastoor, L. Wang, Low-temperature processed solar cells with formamidinium tin halide perovskite/fullerene heterojunctions, Nano Res. 9 (2016) 1570–1577. X. Qiu, B. Cao, S. Yuan, X. Chen, Z. Qiu, Y. Jiang, Q. Ye, H. Wang, H. Zeng, J. Liu, From unstable CsSnI3 to air-stable Cs2SnI6: a lead-free perovskite solar cell light absorber with bandgap of 1.48 eV and high absorption coefficient, Sol. Energy Mater. Sol. Cells 159 (2017) 227–234. D.K. Mohamad, J. Griffin, C. Bracher, A.T. Barrows, D.G. Lidzey, Spray-cast multilayer organometal perovskite solar cells fabricated in air, Adv. Energy Mater. 6 (2016) 1600994. X. Li, D. Bi, C. Yi, J.D. Décoppet, J. Luo, S.M. Zakeeruddin, A. Hagfeldt, M. Grätzel,

[27]

[28]

[29]

[30]

[31]

[32]

[33]

[34]

[35]

171

A vacuum flash–assisted solution process for high-efficiency large-area perovskite solar cells, Science 353 (2016) 6294. C.F.J. Lau, X. Deng, Q. Ma, J. Zheng, J.S. Yun, M.A. Green, S. Huang, A.W.Y. HoBaillie, CsPbIBr2 perovskite solar cell by spray assisted deposition, ACS Energy Lett. 1 (2016) 573–577. Z. Bi, Z. Liang, X. Xu, Z. Chai, H. Jin, D. Xu, J. Li, M. Li, G. Xu, Fast preparation of uniform large grain size perovskite thin film in air condition via spray deposition method for high efficient planar solar cells, Sol. Energy Mater. Sol. Cells 162 (2017) 13–20. Y. Deng, E. Peng, Y. Shao, Z. Xiao, Q. Dong, J. Huang, Scalable fabrication of efficient organolead trihalide perovskite solar cells with doctor-bladed active layers, Energy Environ. Sci. 8 (2015) 1544–1550. M. Zhang, H. Yu, J.H. Yun, M. Lyu, Q. Wang, L. Wang, Facile preparation of smooth perovskite films for efficient meso/planar hybrid structured perovskite solar cells, Chem. Commun. 51 (2015) 10038–10041. K. Hwang, Y.S. Jung, Y.J. Heo, F.H. Scholes, S.E. Watkins, J. Subbiah, D.J. Jones, D.Y. Kim, D. Vak, Toward large scale roll‐to‐roll production of fully printed perovskite solar cells, Adv. Mater. 27 (2015) 1241–1247. J.W. Lee, S.I. Na, S.S. Kim, Efficient spin-coating-free planar heterojunction perovskite solar cells fabricated with successive brush-painting, J. Power Sources 339 (2017) 33–40. N. Ahn, D.Y. Son, I.H. Jang, S.M. Kang, M. Choi, N.G. Park, 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. 137 (2015) 8696–8699. F. Huang, Y. Dkhissi, W. Huang, M. Xiao, I. Benesperi, S. Rubanov, Y. Zhu, X. Lin, L. Jiang, Y. Zhou, A. Gray-Weale, J. Etheridge, C.R. McNeill, R.A. Caruso, U. Bach, L. Spiccia, Y.B. Cheng, Gas-assisted preparation of lead iodide perovskite films consisting of a monolayer of single crystalline grains for high efficiency planar solar cells, Nano Energy 10 (2014) 10–18. X. Wen, S. Huang, S. Chen, X. Deng, F. Huang, Y.B. Cheng, M. Green, A. Ho‐Baillie, Optical probe ion and carrier dynamics at the CH3NH3PbI3 interface with electron and hole transport materials, Adv. Mater. Interfaces 3 (2016) 1600467.