CVD all-vacuum prepared perovskite

Author’s Accepted Manuscript Effect of PbI2 deposition rate on two-step PVD/CVD all-vacuum prepared perovskite Apostolos Ioakeimidis, Christos Christodoulou, Martha Lux-Steiner, Konstantinos Fostiropoulos www.elsevier.com/locate/yjssc

PII: DOI: Reference:

S0022-4596(16)30342-5 http://dx.doi.org/10.1016/j.jssc.2016.08.034 YJSSC19514

To appear in: Journal of Solid State Chemistry Received date: 10 May 2016 Revised date: 19 August 2016 Accepted date: 26 August 2016 Cite this article as: Apostolos Ioakeimidis, Christos Christodoulou, Martha LuxSteiner and Konstantinos Fostiropoulos, Effect of PbI2 deposition rate on twostep PVD/CVD all-vacuum prepared perovskite, Journal of Solid State Chemistry, http://dx.doi.org/10.1016/j.jssc.2016.08.034 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 galley proof before it is published in its final citable 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.

Effect of PbI2 deposition rate on two-step PVD/CVD all-vacuum prepared perovskite Apostolos Ioakeimidis, Christos Christodoulou, Martha Lux-Steiner, Konstantinos Fostiropoulos* Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany *Corresponding author: [email protected]

Abstract In this work we fabricate all-vacuum processed methyl ammonium lead halide perovskite by a sequence of physical vapor deposition of PbI2 and chemical vapour deposition (CVD) of CH3NH3I under a static atmosphere. We demonstrate that for higher deposition rate the (001) planes of PbI 2 film show a higher degree of alignment parallel to the sample’s surface. From X-ray diffraction data of the resulted perovskite film we derive that the intercalation rate of CH3NH3I is fostered for PbI2 films with higher degree of (001) planes alignment. The stoichiometry of the produced perovskite film is also studied by Hard X-ray photoelectron spectroscopy measurements. Complete all-vacuum perovskite solar cells were fabricated on glass/ITO substrates coated by an ultra-thin (5 nm) Zn-phthalocyanine film as hole selective layer. A dependence of residual PbI 2 on the solar cells performance is displayed, while photovoltaic devices with efficiency up to η = 11.6 % were achieved.

Keywords Lead iodide perovskite; perovskite solar cells; PVD; CVD; PbI2 deposition rate; molecular intercalation;

1. Introduction Organometal halide perovskites (OMHPs) materials emerge as a promising absorber for the production of low ,

,

cost, high efficiency solar cells. Their reported high carrier mobility[1] [2] [3] and low recombination rate[4] rocketed the power conversion efficiency[5] .Their implementation as absorber layer in solar cells was first announced by Miyasaka and his colleagues[6] in 2009; since then a variety of OMHP synthesis techniques has been developed[7]. Two alternative synthesis approaches have been described either by one step processing of binary precursor mixtures (e.g., PbI2 and CH3NH3I) or by sequential deposition of the precursors. In the case of sequential deposition, the impact of PbI2 film crystallinity on CH3NH3PbI3 (perovskite) formation has been little ,

investigated[8] [9]. Furthermore, OMHP film properties e.g., grain size, morphology and chemical homogeneity ,

,

,

depend on the production method, influencing significantly its electrical properties. [10] [11] [12] [13]Particularly, it has been proved that the performance of perovskite solar cells (PSC) is considerably affected by unreacted PbI 2 ,

,

[14] [15] [16]. Another main issue toward high performance PSC is the choice of the appropriate hole selective layers (HSL)[17], where alternative low cost metal-phthalocyanines have also been used for this purpose ,

,

,

,

,

,

[18] [19] [20] [21] [22] [23] [24]. Regarding the PSC production, a wet process is usually included either for perovskite or carrier-collection layers fabrication, while there have been only few reports on fully-vacuum ,

,

,

,

processed PSC[19] [25] [26] [27] [28].

In this work we prepared polycrystalline PbI2 layers by physical vapour deposition (PVD) and we investigated the impact of the applied deposition rate (Rdep) on the crystallites’ orientation and the morphology of the formed films. Furthermore, such films were exposed to a static atmosphere of CH3NH3I that intercalated into PbI2 in a chemical vapour deposition process (CVD) forming perovskite. PbI2 residues in perovskite film were studied using X-ray techniques, and correlated with the PbI2 deposition rate. In addition, the stoichiometry of a perovskite film is probed by means of Hard X-ray photoelectron spectroscopy (HAXPES).

We finally produced all-vacuum processed PSCs by applying an ultra-thin (5 nm) film of Zn-phthalocyanine (ZnPc) as HSL, and we examine the influence of PbI2 residues on solar cell performance.

2. Methods For the sample preparation glass and pre-patterned glass/ITO (sheet resistance 5 ohm/□) substrates were °

cleaned by ultra-sonication in acetone, ethanol and deionized water and then dried on a hotplate at 130 C for 15 min.

2.1 Fabrication and characterization of PbI2 and perovskite films Glass and pre-patterned ITO/glass (sheet resistance 5 ohm/□) substrates were cleaned by ultra-sonication in o

acetone, ethanol and water and then dried on a hotplate at 130 C for 15 min. -6

For the preparation of PbI2 films, 90 nm was vacuum thermally deposited (base pressure < 10 mbar) on room temperature glass substrates at rates R dep = 3.5, 4.5, 5.2 Å/sec.Four perovskite film samples were prepared on glass substrates using the following steps: a) Deposition of 90 nm PbI2 at rate Rdep = 3.5, 4.5 Å/sec (one sample each) and another two samples at Rdep = 5.2 Å/sec. b) Subsequently, the glass/PbI2 samples were placed 1 cm above and facing CH3NH3I powder in a closed chamber. Then, the chamber was evacuated (base pressure 10

-2

o

mbar) and heated to 120 C to generate a respective CH3NH3I vapour pressure in order to initiate molecular intercalation into the PbI2 layer. Three of the samples (Rdep = 3.5, 4.5, 5.2 Å/sec) were intercalated for Tint = 55 min, while the fourth (Rdep = 5.2 Å/sec) for Tint = 65 min. X-ray diffraction (XRD), grazing incident X-ray diffraction (GIXRD) and omega scan (Rocking curve, RC) measurements were performed on a PANalytical X’Pert Pro diffractometer with parallel beam optics and Cu K α radiation (λ = 1.54 Å) source. Atomic force microscopy (AFM) images were obtained using Anfatec Level in ‘tapping’ mode. Hard X-ray photoelectron spectroscopy (HAXPES) measurements were performed at the endstation HIKE, at the synchrotron facility BESSY II, Berlin. 2.2 Fabrication and characterization of perovskite solar cells An ultrathin layer of 5 nm of ZnPc HSL was deposited by thermally sublimation under vacuum (base pressure < -7

10 mbar) onto glass/ITO substrates at a rate of 0.2 Å/sec. Following the procedures described in section 2.1, perovskite films were grown on the HSL. Subsequently, all samples were transferred into a high vacuum -7

chamber (base pressure < 10 mbar) where 25 nm C60 followed by 10 nm bathophenanthroline buffer (Bphen) were thermally deposited, both at a rate of 0.2 Å/sec. Finally, 100 nm Al back contact was thermally deposited, 2

forming an active area of 3.2 mm . The J-V curves of the PSC were obtained using a Keithley Series 2004 2

Source meter under a Xe lamp of 100 mW/cm adjusted intensity.

3. Results and discussion 3.1 Effect of PbI2 deposition rate on crystallite orientation and morphology Figure 1 presents X-ray diffraction (XRD) data of PbI2 films thermally deposited at three different rates Rdep = 3.5, 4.5 and 5.2 Å/sec. The inset graph displays the corresponding grazing incident X-ray diffraction (GIXRD) data at

incident angle ω = 0.3 °. The GIXRD data show clearly that for each PbI2 film only one strong peak appears which can be assigned to (001) planes, confirming the preferential growth of PbI 2 along the c-axis direction. XRD data provide crystallographic information of (001) lattice planes along the perpendicular direction to the sample surface, where each peak could be described by a Gaussian function. From the fitted parameters (Table 1) we observe that the normalized peak intensity increases as we increase R dep, while the Full Width Half Maximum (FWHM) of the peaks decreases.

Figure 1. X-ray analysis of PbI2 films on glass deposited at different rates. (a) Experimental data (dots) and Gaussian fits (lines) of XRD (001) PbI2 peaks. The inset graph shows the corresponding GIXRD diffraction pattern. (b) Rocking curves (RC) of the peaks in (a).

Table 1. Gaussian fit results of (001) XRD peaks from PbI2 films deposited at different rates Norm. Rdep (Å/sec)

2theta (deg.)

FWHM (deg.) intensity

3.5

12.67

0.114

46.31

4.5

12.68

0.103

91.31

5.2

12.68

0.100

100

Supporting measurements on PbI2 film were performed by XRD ω-scan (rocking curve, RC) at the (001) peak position of each sample, in order to investigate lattice stacking along [001] direction. Figure 1(b) presents the normalized RCs of the PbI2 films deposited at different rates showing that for higher rates the FWHM of the peaks decrease. The XRD and RC findings show that a higher degree of (001) lattice planes have been arranged parallel to substrate’s surface. Additionally, 5x5 μm AFM topography images (Figure 2) were obtained for each sample. We notice that for the Rdep = 3.5 Å/sec the film exhibits large grains on its surface in contrast to the higher Rdep films, where the grains are considerably fewer and smaller in size. As a result the root mean square roughness (RMS) of Rdep = 4.5, 5.2 Å/sec films is almost half (3 nm and 2.8 nm, respectively) compared to the Rdep = 3.5 Å/sec film which is RMS = 5.8 nm.

Figure 2. AFM images (5x5 μm) of PbI2 films deposited at rates (a) 3.5 (b) 4.5 and (c) 5.2 Å/sec. Combining the above results we derive that for increased Rdep a smoother film with higher degree of crystallite alignment was produced, pointing to the formation of a more compact film. This could be ascribed to the heat up of the growing film due the high condensation energy induced by increased Rdep. These findings are in good agreement with previous work by M.Schieber et al.[29], who has demonstrated comparable effect by heating up the substrate during PbI2 growth.

3.2 Effect of PbI2 crystallite orientation on perovskite formation

Figure 3. GIXRD pattern of perovskite film samples S1, S2, S3 and S4 measured at incident angles (a) 0.5° and (b) 0.3 °.

Table 2. The preparation parameters deposition rate (Rdep) and intercalation time (Tint) of perovskite film samples. Sample

Rdep (Å/sec)

Tint (min)

S1

3.5

55

S2

4.5

55

S3

5.2

55

S4

5.2

65

Four perovskite film samples (Table 2) were prepared on four glass substrates following the procedure described in section 2.1. Figure 3 displays GIXRD data of the films measured at two different grazing incident angles (ω = 0.3 ° and 0.5 °). Both measurements show the same pattern with peak positions at 14.06 °, 20.06 °, 24.58 °, 28.52 °, 31.81 °, 35.08 °, 40.67 ° and 43.37 ° that can be assigned to (110), (200), (202), (220), (310), (312), (224), (330) diffraction peaks, respectively, corresponding to the tetragonal perovskite structure which has been

analyzed in detail by Stoumpos, C. C., Malliakas, C. D. & Kanatzidis.[30]. In contrary to the ω = 0.3 ° pattern, an additional diffraction peak at 12.68° appears for ω = 0.5°, suggesting the existence of non-intercalated PbI2 residues at the bottom of the film. Interestingly, this additional PbI2 peak is significantly reduced in samples with higher Rdep indicating less PbI2 residue. Therefore, the higher degree of PbI2 (001) planes alignment parallel to the sample’s surface fosters the intercalation rate of CH3NH3I into the PbI2 layer. The conclusion is in consistent with the findings reported by S.Ahmad et al.[31].For S4 we obtained similar diffraction pattern but the additional PbI2 peak at ω = 0.5 ° is further reduced. Clearly, an even thinner PbI2 residue layer remained at the bottom of the film due to prolongation of the intercalation time to Tint= 65 min. 3.3

Stoichiometry of all-vacuum prepared perovskite films

According to the x-ray diffraction studies described above the S4 growth conditions yield the most completely intercalated perovskite layer. Therefore, HAXPES measurements were performed on a perovskite film corresponding to S4 growth conditions. The excitation energy had been set to 4000 eV, in order to achieve an information depth extending multiple layers below the surface ( ~ 10 nm )[32]. Figure 4(a, b) shows the Pb4f (spin-orbit doublet: Pb4f7/2 and Pb4f5/2) and I3d (spin-orbit doublet I3d3/2 and I3d5/2) core levels. The spectra were deconvoluted using a single Voigt function for each distinct core level peak. The peak at binding energy BE = 138.0 eV is attributed to emissions stemming from Pb

2+

in perovskite. This is in reasonable agreement to the

values measured by R. Lindbland et al.[33] using HAXPES at the same endstation. Interestingly, there are no identifiable emissions (within the sensitivity limits) from atomic Pb or Pb attributed to emissions stemming from I

3+

2+

in PbI2. The emission at 619.8 eV is

in the perovskite structure as well [33]. Taking the spectral area ratios

for Pb4f7/2 and I3d5/2 (and normalizing them to the cross sections of the core levels at hv = 4000 eV), we find a ratio 1:2.9. This suggests that a stoichiometric perovskite film was formed.

Figure 4c shows the valence level spectra taken at hv = 4000 eV. The valence band onset for the perovskite film is at 0.92 eV with respect to its Fermi level, which additionally evidences that the perovskite is stoichiometric (I:Pb 3:1), agreeing with the findings from core level spectra reported by Wang, Q. et al. [34]

Figure 4. Hard X-Ray photoemission spectra collected at excitation energy 4000 eV. a) Pb4f core levels with binding energy of the Pb4f7/2 at 138 eV (fitted red line), b) I3d core levels with the binding energy of I3d 5/2 at 619.8 eV (fitted red line) and c) valence band spectrum, showing the valence band onset at 0.92 eV with respect to the Fermi level (EF). 3.4 All-vacuum processed PSC Four PSC (D1, D2, D3 and D4) with perovskite absorber corresponding to S1, S2, S3 and S4 growing parameters were fabricated, in order to examine the impact of the remaining PbI2 amount on their electrical characteristic. Each PSC were fabricated on ITO substrates, which serve as the anode of the device. To better match the energy levels at the interface of anode and perovskite, we introduced 5 nm of ZnPc which acts as HSL due to its well aligned HOMO(-5.28eV)[35] with the valence band onset of perovskite (-5.4eV)[36]. To complete the devices, 25 nm of C60 followed by 10 nm of Bphen buffer and 100nm of Al were thermally deposited. Figure 5 2

displays the current density-voltage (J-V) characteristic curves of the PSC under 100 mw/cm light illumination and the corresponding parameters are shown in Table 3. The PSC with lower Rdep (D1) yields lower performance (η=6.6 %) in comparison to those with increased Rdep (D2, D3), which achieve η = 9.5 % and η = 9.7 %, respectively. We notice that the open-circuit Voltage(Voc) in all three PSC is similar, while on the other hand the short-circuit current (Jsc) of D2 and D3 is significantly increased by 25 % and 22 % as well as the Fill Factor (FF) by 18 % and 20 %, respectively. The higher Jsc is ascribed to increased light absorption due to more complete

formation of perovskite (as shown in section 3.2), whereas the increased FF is attributed to the lower series resistance and higher shunt resistance due to less non-intercalated PbI2 residue at the bottom of the film. D4 PSC gives a significantly increased Voc = 0.96 V and a slightly increased FF. On the other hand Jsc is affected only marginally pointing to reduction of charge carrier recombination due to even less non-intercalated PbI2. The D4 device yields a power conversion efficiency of η = 11.6 % which is the higher in this study.

2

Figure 5. J-V curves of PSC under 100 mW/cm illumination. D1, D2, D3 and D4 PSC correspond to perovskite absorber with growth conditions S1, S2, S3 and S4, respectively.

2

Table 3. J-V characteristics of PSCs under 100 mW/cm illumination FF

η

Rsh

(mA/cm )

(%)

(%)

(KΩ·cm )

(Ω·cm )

0.87

13.79

55

6.6

0.61

15.39

D2

0.85

17.20

65

9.5

1.23

6.37

D3

0.87

16.85

66

9.7

1.18

7.00

D4

0.96

17.26

70

11.6

0.99

4.07

Voc

Jsc

(V) D1

sample

2

Rs 2

2

4. Conclusion In conclusion, we have prepared perovskite layers by a two-step vacuum deposition process. In first step, PbI2 was deposited by PVD at three different rates (Rdep = 3.5, 4.5 and 5.2 Å/sec). For increased Rdep the film exhibit a lower surface roughness with higher degree of PbI2 (001) planes alignment parallel to substrate’s surface. As second step, perovskite films were formed by applying a CVD process under a static CH3NH3I atmosphere. The higher rate deposited PbI2 films (yielding higher (001) plane alignment) were found to foster the intercalation rate of CH3NH3I resulting in formation of perovskite layers with less residual PbI 2. An even deeper intercalation was achieved by prolonging the intercalation time to T int = 65 min. HAXPES measurements on this sample revealed the formation of a stoichiometric perovskite film, with a valence band onset of 0.92 eV with respect to its Fermi level. Finally, all-vacuum perovskite solar cells were fabricated using 5nm ZnPc layer as hole selective layer. The influence of residual PbI2 on the PSC device characteristics was demonstrated with the best performing device 2

(Voc = 0.96 V, Jsc = 17.3 mA/cm , FF = 70 %, η = 11.6 %) being obtained for perovskite preparation parameters Rdep = 5.2 Å/sec and Tint = 65 min.

Acknowledgements Funding: This research was partially financially supported by the Helmholtz-Energy Alliance “Hybrid photovoltaics” and by the “GR-Elect” project (BMBF Contract No. 03X0142)

References [1]

C. Motta, F. El-Mellouhi, S. Sanvito, Charge carrier mobility in hybrid halide perovskites., Sci. Rep. 5 (2015) 12746. doi:10.1038/srep12746.

[2]

C. Wehrenfennig, G.E. Eperon, M.B. Johnston, H.J. Snaith, L.M. Herz, High charge carrier mobilities and lifetimes in organolead trihalide perovskites, Adv. Mater. 26 (2014) 1584–1589. doi:10.1002/adma.201305172.

[3]

E. Edri, S. Kirmayer, S. Mukhopadhyay, K. Gartsman, G. Hodes, D. Cahen, Elucidating the charge carrier separation and working mechanism of CH3NH3PbI(3-x)Cl(x) perovskite solar cells., Nat. Commun. 5 (2014) 3461. doi:10.1038/ncomms4461.

[4]

T.J. Savenije, C.S. Ponseca, L. Kunneman, M. Abdellah, K. Zheng, Y. Tian, Q. Zhu, S.E. Canton, I.G. Scheblykin, T. Pullerits, A. Yartsev, V. Sundström, Thermally activated exciton dissociation and recombination control the carrier dynamics in organometal halide perovskite, J. Phys. Chem. Lett. 5 (2014) 2189–2194. doi:10.1021/jz500858a.

[5]

W.S. Yang, J.H. Noh, N.J. Jeon, Y.C. Kim, S. Ryu, J. Seo, S. Il Seok, High-performance photovoltaic perovskite layers fabricated through intramolecular exchange, Science (80-. ). 348 (2015) 1234–1237. doi:10.1126/science.aaa9272.

[6]

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. doi:10.1021/ja809598r.

[7]

T. Song, Q. Chen, H.H.-P. Zhou, C. Jiang, H.-H. Wang, Y. (Michael) Yang, Y. Liu, J. You, Y. Yang, Y. Liu, J. You, Y. (Michael) Yang, Y. Liu, J. You, Y. Yang, Perovskite solar cells: film formation and properties, J. Mater. Chem. A. 3 (2015) 9032–9050. doi:10.1039/C4TA05246C.

[8]

H.-S. Ko, J.-W. Lee, N.-G. Park, 15.76% efficiency perovskite solar cells prepared under high relative humidity: importance of PbI2 morphology in two-step deposition of CH3NH3PbI3, J. Mater. Chem. A. 3 (2015) 8808–15. doi:10.1039/C5TA00658A.

[9]

F. Fu, L. Kranz, S. Yoon, J. Löckinger, T. Jäger, J. Perrenoud, T. Feurer, C. Gretener, S. Bücheler, A.N.

Tiwari, Controlled growth of PbI2 nanoplates for rapid preparation of CH3NH3PbI3 in planar perovskite solar cells, Phys. Status Solidi. 3 (2015) 1–10. doi:10.1002/pssa.201532442. [10]

T. Salim, S. Sun, Y. Abe, A. Krishna, A.C. Grimsdale, Y.M. Lam, Perovskite-based solar cells: impact of morphology and device architecture on device performance, J. Mater. Chem. A. 3 (2015) 8943–8969. doi:10.1039/c4ta05226a.

[11]

Y. Fu, F. Meng, M.B. Rowley, B.J. Thompson, M.J. Shearer, D. Ma, R.J. Hamers, J.C. Wright, S. Jin, Solution growth of single crystal methylammonium lead halide perovskite nanostructures for optoelectronic and photovoltaic applications, J. Am. Chem. Soc. 137 (2015) 5810–5818. doi:10.1021/jacs.5b02651.

[12]

W. Nie, H. Tsai, R. Asadpour, A.J. Neukirch, G. Gupta, J.J. Crochet, M. Chhowalla, S. Tretiak, M.A. Alam, H. Wang, High-efficiency solution-processed perovskite solar cells with millimeter-scale grains, Science (80-. ). 347 (2015) 522–525.

[13]

Z. Xiao, C. Bi, Y. Shao, Q. Dong, Q. Wang, Y. Yuan, C. Wang, Y. Gao, J. Huang, Efficient, high yield perovskite photovoltaic devices grown by interdiffusion of solution-processed precursor stacking layers, Energy Environ. Sci. 7 (2014) 2619. doi:10.1039/c4ee01138d.

[14]

D.H. Cao, C.C. Stoumpos, C.D. Malliakas, M.J. Katz, O.K. Farha, J.T. Hupp, M.G. Kanatzidis, Remnant PbI2, an unforeseen necessity in high-efficiency hybrid perovskite-based solar cells?, APL Mater. 2 (2014) 1–8. doi:10.1063/1.4895038.

[15]

S. Wang, W. Dong, X. Fang, Q. Zhang, S. Zhou, Z. Deng, R. Tao, J. Shao, R. Xia, C. Song, L. Hu, J. Zhu, The credible evidence for passivation effect of remnant PbI2 in CH3NH3PbI3 films for improving the performance of perovskite solar cells, Nanoscale. (2016). doi:10.1039/C5NR08344C.

[16]

Q. Chen, H.P. Zhou, T.B. Song, S. Luo, Z.R. Hong, H.S. Duan, L.T. Dou, Y.S. Liu, Y. Yang, Controllable Self-Induced Passivation of Hybrid Lead Iodide Perovskites toward High Performance Solar Cells, Nano Lett. 14 (2014) 4158–4163. doi:Doi 10.1021/Nl501838y.

[17]

Z. Yu, L. Sun, Recent Progress on Hole-Transporting Materials for Emerging Organometal Halide Perovskite Solar Cells, Adv. Energy Mater. 5 (2015) 1500213. doi:10.1002/aenm.201500213.

[18]

J. Seo, N.J. Jeon, W.S. Yang, H.W. Shin, T.K. Ahn, J. Lee, J.H. Noh, S. Il Seok, Effective electron blocking of CuPC-doped spiro-OMeTAD for highly efficient inorganic-organic hybrid perovskite solar cells, Adv. Energy Mater. 5 (2015) 1–6. doi:10.1002/aenm.201501320.

[19]

W. Ke, D. Zhao, C.R. Grice, A.J. Cimaroli, J. Ge, H. Tao, H. Lei, G. Fang, Y. Yan, Efficient planar perovskite solar cells using room-temperature vacuum-processed C60 electron selective layers, J. Mater. Chem. A. 3 (2015) 23888–23894. doi:10.1039/C5TA04313A.

[20]

Q.-K. Wang, R.-B. Wang, P.-F. Shen, C. Li, Y.-Q. Li, L.-J. Liu, S. Duhm, J.-X. Tang, Energy Level Offsets at Lead Halide Perovskite/Organic Hybrid Interfaces and Their Impacts on Charge Separation, Adv. Mater. Interfaces. 2 (2015) 1400528. doi:10.1002/admi.201400528.

[21]

C.V. Kumar, G. Sfyri, D. Raptis, E. Stathatos, P. Lianos, Perovskite solar cell with low cost Cuphthalocyanine as hole transporting material, RSC Adv. 5 (2015) 3786–3791. doi:10.1039/C4RA14321C.

[22]

F. Javier Ramos, M. Ince, M. Urbani, A. Abate, M. Gratzel, S. Ahmad, T. Torres, M.K. Nazeeruddin, Nonaggregated Zn(ii)octa(2,6-diphenylphenoxy) phthalocyanine as a hole transporting material for efficient perovskite solar cells, Dalt. Trans. 44 (2015) 10847–10851. doi:10.1039/C5DT00396B.

[23]

M. Sun, S. Wang, Y. Xiao, Z. Song, X. Li, Titanylphthalocyanine as hole transporting material for perovskite solar cells, J. Energy Chem. 24 (2015) 756–761. doi:10.1016/j.jechem.2015.10.020.

[24]

A. Suzuki, T. Kida, T. Takagi, T. Oku, Effects of hole-transporting layers of perovskite-based solar cells, Jpn. J. Appl. Phys. 55 (2016) 02BF1. doi:10.7567/JJAP.55.02BF01.

[25]

H. Hu, D. Wang, Y. Zhou, J. Zhang, S. Lv, S. Pang, X. Chen, Z. Liu, N.P. Padture, G. Cui, Vapour-based processing of hole-conductor-free CH 3 NH 3 PbI 3 perovskite/C 60 fullerene planar solar cells, RSC Adv. 4 (2014) 28964. doi:10.1039/C4RA03820G.

[26]

L.E. Polander, P. Pahner, M. Schwarze, M. Saalfrank, C. Koerner, K. Leo, Hole-transport material variation in fully vacuum deposited perovskite solar cells, APL Mater. 2 (2014) 081503. doi:10.1063/1.4889843.

[27]

B.S. Kim, T.M. Kim, M.S. Choi, H.S. Shim, J.J. Kim, Fully vacuum-processed perovskite solar cells with high open circuit voltage using MoO3/NPB as hole extraction layers, Org. Electron. 17 (2015) 102–106.

doi:10.1016/j.orgel.2014.12.002. [28]

D. Yang, Z. Yang, W. Qin, Y. Zhang, S. (Frank) Liu, C. Li, Alternating precursor layer deposition for highly stable perovskite films towards efficient solar cells using vacuum deposition, J. Mater. Chem. A. 3 (2015) 9401–9405. doi:10.1039/C5TA01824B.

[29]

M. Schieber, N. Zamoshchik, O. Khakhan, A. Zuck, Structural changes during vapor-phase deposition of polycrystalline-PbI2 films, J. Cryst. Growth. 310 (2008) 3168–3173. doi:10.1016/j.jcrysgro.2008.02.030.

[30]

C.C. Stoumpos, C.D. Malliakas, M.G. Kanatzidis, Semiconducting tin and lead iodide perovskites with organic cations: Phase transitions, high mobilities, and near-infrared photoluminescent properties, Inorg. Chem. 52 (2013) 9019–9038. doi:10.1021/ic401215x.

[31]

S. Ahmad, P.K. Kanaujia, W. Niu, J.J. Baumberg, G.V. Prakash, In Situ Intercalation Dynamics in Inorganic − Organic Layered Perovskite Thin Films, ACS Appl. Mater. Interfaces. 6 (2014) 10238–10247. http://dx.doi.org/10.1021/am501568j.

[32]

H. Shinotsuka, S. Tanuma, C.J. Powell, D.R. Penn, Calculations of electron stopping powers for 41 elemental solids over the 50 eV to 30 keV range with the full Penn algorithm, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms. 270 (2012) 75–92. doi:10.1016/j.nimb.2011.09.016.

[33]

R. Lindblad, D. Bi, B.W. Park, J. Oscarsson, M. Gorgoi, H. Siegbahn, M. Odelius, E.M.J. Johansson, H. Rensmo, Electronic structure of TiO2/CH3NH3PbI3 perovskite solar cell interfaces, J. Phys. Chem. Lett. 5 (2014) 648–653. doi:10.1021/jz402749f.

[34]

Q. Wang, Y. Shao, H. Xie, L. Lyu, X. Liu, Y. Gao, J. Huang, Qualifying composition dependent p and n self-doping in CH3NH3PbI3, Appl. Phys. Lett. 105 (2014) 163508. doi:10.1063/1.4899051.

[35]

Gao W., Kahn A. , Electronic structure and current injection in zinc phthalocyanine doped with tetrafluorotetracyanoquinodimethane: Interface versus bulk effects, Org.Electronics 3, (2002), 53-65, doi:10.1016/S1566-1199(02)00033-2

[36]

Lin Q., Armin A, Nagiri R.C.R, Burn P. L., Meredith P., Electro-optics of perovskite solar cells , Nat. phot. 9, (2015) 106-112 doi:10.1038/nphoton.2014.284.

A two-step PVD/CVD processed perovskite film with the CVD intercalation rate of CH3NCH3 molecules been fostered by increasing the PVD rate of PbI2 and prolonging the CVD time.

Graphical Abstract

Highlights ● A simple PVD/CVD process for production of perovskite films. ● PbI2 crystallite alignment of (001) planes parallel to the substrate surface improves significantly when PVD rate is increased, fostering intercalation rate of CH3NH3I.

● Stoichiometric CH3NH3PbI3 is formed through this process capable for photovoltaic application ● PbI2 residue remained at the bottom of the film can be minimized improving solar cell’s performance, drastically.