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Hole-conductor free ambient processed mixed halide perovskite solar cells
Materials Letters 245 (2019) 226–229
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Hole-conductor free ambient processed mixed halide perovskite solar cells Suresh Maniarasu, Manoj Kumar Rajbhar, Reshma K. Dileep, Easwaramoorthi Ramasamy, Ganapathy Veerappan ⇑ Centre for Solar and Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur P.O, Hyderabad 500005, India
a r t i c l e
i n f o
Article history: Received 31 December 2018 Received in revised form 6 March 2019 Accepted 7 March 2019 Available online 9 March 2019 Keywords: Perovskite solar cells Ambient processed Mixed halide perovskite Hole conductor free solar cells
a b s t r a c t In the past several years, organic-inorganic halide based perovskites has become an exciting topic in the field of photovoltaic community. Conventional perovskite solar cells (PSC) use 2,20 ,7,70 -Tetrakis[N,N-di(4methoxyphenyl)amino]-9,90 -spirobifluorene (spiro-OMeTAD) as a hole transporting layer (HTL), but the cost and stability of the polymeric HTL affects the scaling-up of PSC. This work, reports a hole- conductor free-ambient processed mixed halide PSCs with promising efficiency by tuning the morphology of the perovskite films by employing different deposition techniques (one step, two-step and dip coating method). In the dip coating method, unique cuboid structured films with good absorption and pin hole free films were obtained. The photovoltaic performances of the devices made by various deposition methods were measured at 1 sun illumination under standard conditions and achieved upto 6.5%. Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction Organic-Inorganic hybrid halide perovskite materials have been widely used in photovoltaic field due to their fascinating properties. In a short span of time, the efficiency of perovskite photovoltaic cell soared from 3.1% to 23.1% [1–3]. The instability of perovskite solar cells (PSCs) in the presence of organic hole transporting material (HTM) and cost of the metal cathode and HTM materials limits the possibilities of large scale fabrication and commercialization of PSCs. This led to the evolution of hole conductor free devices with enhanced stability [4]. Various methods are being used to enhance the performance of the PSC, which includes engineering the perovskite material by inclusion of new materials, surface engineering etc. [5,6]. Altering the lead content and inclusion of new halides tunes the electronic properties such as band gap and diffusion length of the material. Addition of PbCl2 in small quantities to MAPbI3 tunes the diffusion lengths from 100 nm to 1 mm [7]. Although, several reports are available for mixed halide perovskites for conventional PSC, but the exploration of such mixed halide perovskite in ambient processed HTM free PSCs are scarce [8]. In this letter, ambient processed mixed halide perovskite (MAPbI3xClx) films were prepared by three different depositing techniques (one step, two-step and dip coating). Organic⇑ Corresponding author. E-mail address: [email protected] (G. Veerappan). https://doi.org/10.1016/j.matlet.2019.03.021 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
Inorganic perovskite films synthesised by dip coating technique yielded highly ordered cuboid morphology compared to the one step and two step spin coating techniques [8]. This highly ordered cuboid morphology resulted in, increased current density due to improved charge carrier transport properties and lesser number of grain boundaries [8,9]. Organic-Inorganic PSC’s fabricated with these different techniques are compared and analysed.
2. Results & discussion The schematic diagram in Fig. 1 shows three different deposition techniques as described in the experimental section. To gain insight into the influence of various deposition techniques, we first investigated the phase formation and crystallinity of the samples. Fig. 2(e) shows the XRD patterns of the mixed halide perovskite (MAPbI3xClx) prepared by one step, two step and dip coating techniques and annealed at 120 °C/30 min. The diffraction peaks at 2h = 14.01°, 28.19° and 43.09°, corresponds to (1 1 0), (2 2 0) and (3 3 0) diffraction peaks of mixed halide perovskite (MAPbI3xClx) with tetragonal crystal structure [10–12]. The colour of the film varied with different deposition techniques. In spin coating, the film was transparent and slowly changes to dark brown after heating at 120 °C/30 min, but in case of dip coating, the films immediately changed to dark brown colour in fraction of seconds. Fig. S1 illustrate the typical absorption spectra of the film prepared by the different deposition techniques. The
S. Maniarasu et al. / Materials Letters 245 (2019) 226–229
227
Fig. 1. Schematics of deposition by (a) one-step (b) two-step and (c) dip coating methods.
Fig. 2. Surface Morphology of (a) pristine PbCl2 film. (b) one-step, (c) two-step, (d) dip coated perovskite film, (e) XRD patterns of MAPbI3xClx made with one step, two step and dip coating method.
band gap of this mixed halide perovskite was evaluated as 1.55 eV by the tauc plot which were similar to the reported values [13]. Effect of different deposition techniques on morphology of the films were further analysed with the help of FE-SEM images. Fig. 2 shows the surface morphology of the pristine PbCl2 film
and different deposition technique films. When PbCl2 was used over the TiO2 for the mixed halide perovskite, small granular grain morphology with proper coverage was observed. Fig. 2(b) shows surface morphology of the film prepared by 1 M of PbCl2 and 3 M of methylammonium iodide (MAI) constitutes of big grain size
228
S. Maniarasu et al. / Materials Letters 245 (2019) 226–229
Fig. 3. Current-Voltage (I-V) studies of MAPbI3xClx prepared with three different deposition techniques, (b) Internal photon conversion efficiencies of mixed halide devices.
Table 1 Photovoltaic performances of mixed halide devices fabricated with different techniques. Deposition Methods
JSC (mA/cm2)
VOC (V)
FF (%)
Η (%)
Dip Coating Two-step One-step
13.9 10.3 8.6
0.765 0.738 0.691
52.2 46.1 40.2
6.5 4.1 2.8
Where, JSC – current density; VOC – open circuit voltage; FF – fill factor and g – power conversion efficiency.
but the presence of pin holes leads to recombination of charge carriers [12]. Fig. 2(c) shows the film prepared by spin coating, which exhibits column like morphology with small pin holes. Fig. 2(d) shows the film morphology of dip coating, which was made by directly dipping the PbCl2 film into the MAI solution. According to the reported literature, the morphology of cuboids improves the light absorption and electrons could be easily transferred to the anode through the grain boundaries, which avoids the recombination of charge carriers [14]. Size of the cuboids varies as a function of dipping time and the concentration of MAI, lower concentrations can yield cuboids of size up to 1 mm [14]. These FE-SEM results confirm that dip coating yields better films and photovoltaic performance, compared to the other two techniques due to high crystallinity with large grain size [14]. Spectra in Fig. 3(a) shows the photovoltaic performances are strongly influenced by the deposition techniques and their corresponding solar cell parameters are tabulated in Table 1. Despite the complete conversion of perovskite (Fig. 2e) by one step method, the J-V parameters of the devices are poor, because of the non-uniform perovskite film, which has large pin holes and consequently increases the recombination and affects the power conversion efficiency (PCE). Whereas, the presence of excess amount of PbI2 has been observed in the perovskite film to be beneficial, but why is still unclear. The remnant PbI2 can be observed at the grain boundaries which passivates the TiO2 interface resulted in, enhanced charge transfer and less recombination. In addition, the perovskite films with small amount of excess PbI2 showed highly ordered morphology which is beneficial for photovoltaic performance [15]. Devices made with spin coating had slightly improved photovoltaic parameters, due to the column like morphology and proper coverage. Compared to the above mentioned techniques, the dip coating method shows better improvement in the current density and other parameters. The higher
current density (JSC) in dip coating method might be due to the light scattering by the cuboids, which ascribes to high absorbance and low series resistance in the device [14]. Due to the cuboid surface morphology, it yields good absorption and pin hole free film yielding such high current and efficiency. The high quality films helps in reducing the recombination of charge carriers, the strong interfaces help in better charge extraction leading to enhanced voltage and current density. Larger cuboid perovskites employed PSCs exhibit a higher fill factor due to the less number of grain boundaries, reducing the charge transfer resistance and the series resistance compared to the perovskite films developed by other two techniques resulting in enhanced fill factor [14]. Fig. 3b shows the external quantum efficiency of the mixed halide perovskite for three deposition techniques. The internal photon conversion efficiency (IPCE) spectra of the solar cell fabricated by one step method were lower when compared with the other two techniques due to non-uniform film morphology. Due to the better surface morphology, the device prepared by spin coating shows good photon conversion compared to the one step technique. The device fabricated by dip coating technique has harvested more than 60% of the incident photons because of the cubic structured morphology, which increases the light absorption range resulting in excellent charge transport to electrodes [13]. The IPCE spectrum of these devices is similar to their absorption spectra (i.e. more absorption in the range of 380 nm–520 nm). Low response of the IPCE spectrum in the wavelength range of 550 nm–750 nm is due the absorption of lead iodide or recombination of some low energy photons in HTM free devices. The integrated JSC value calculated from the IPCE spectra, which is slightly lower than the values obtained from the IV characteristics for all three deposition techniques.
3. Conclusion We studied the influence of mixed halide perovskite by different deposition techniques and its photovoltaic performance on hole conductor free PSC’s fabricated under ambient conditions. Cuboidal nanostructured mixed halide films were yielded by dip coating method, which has high uniformity, pin hole free and large grain size. The cuboidal structured perovskite film results in a low resistance and better performing devices with high fill factor, JSC and open circuit voltage (VOC) when compared with the other devices. With further optimization, PCE of these devices can be doubled.
S. Maniarasu et al. / Materials Letters 245 (2019) 226–229
Conflicts of interest None Acknowledgments Dr. G. V acknowledges the Department of Science and Technology, New Delhi, India for the financial support through DSTINSPIRE Faculty award (IFA 14-MS-28), DST-SYST (SP/ YO/012/2017 (G)) and TRC (AI/1/65/ARCI/2014). G. V. and coauthors extend their acknowledgment to the Director, ARCI. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.03.021. References: [1] M. Wright, A. Uddin, Organic – inorganic hybrid solar cells: a comparative review, Sol. Energy Mater. Sol. Cells 107 (2012) 87–111. [2] S. Maniarasu, T.B. Korukonda, V. Manjunath, M. Ramesh, G. Veerappan, E. Ramasamy, Recent advancement in metal cathode and hole-conductor-free perovskite solar cells for low-cost and high stability: a route towards commercialization, Renew. Sustain. Energy Rev. 82 (2017) 845–857. [3] https://www.nrel.gov/ncpv/images/efficiency_chart.jpg. [4] H.S. Kim, C.R. Lee, J.H. Im, K.B. Lee, T. Moehl, A. Marchioro, S.J. Moon, R. Humphry-Baker, J.H. Yum, J.E. Moser, M. Gratzel, N.G. Park, Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9%, Sci. Rep. 2 (2012) 591–597.
229
[5] J.-F. Wang, L. Zhu, B.-G. Zhao, Y.-L. Zhao, Y.-L. Zhao, X.-Q. Gu, Y.-H. Qiang, Surface engineering of perovskite films for efficient solar cells, Sci. Rep. 7 (14478) (2017) 1–9. [6] V.L. Pool, A. Gold-Parker, M.D. McGehee, M.F. Toney, Chlorine in PbCl2-derived hybrid-perovskite solar absorbers, Chem. Mater. 27 (2015) 7240–7243. [7] N.D. Pham, V.T. Tiong, P. Chen, L. Wang, G.J. Wilson, J. Bella, H. Wang, Enhanced perovskite electronic properties via a modified lead(II) chloride Lewis acid– base adduct and their effect in high-efficiency perovskite solar cells, J. Mater. Chem. A 5 (2017) 5195–5203. [8] P. Docampo, F. Hanusch, S.D. Stranks, M. Döblinger, J.M. Feckl, M. Ehrensperger, N.K. Minar, M.B. Johnston, H.J. Snaith, T. Bein, Solution deposition-conversion for planar heterojunction mixed halide perovskite solar cells, Adv. Energy Mater. 1400355 (2014) 1–5. [9] S.T. Williams, F. Zuo, C.C. Chueh, C.Y. Liao, P.W. Liang, A.K.Y. Jen, Role of chloride in the morphological evolution of organo-lead halide perovskite thin films, J. Am. Chem. Soc. 8 (2014) 10640–10654. [10] J. Liu, J. Lin, Q. Xue, Q. Ye, X. He, L. Ouyang, D. Zhuang, C. Liao, H.L. Yip, J. Mei, W.M. Lau, Growth and evolution of solution-processed CH3NH3PbI3-xClx layer for highly efficient planar-heterojunction perovskite solar cells, J. Power Sources 301 (2016) 242–250. [11] J. Burschka, N. Pellet, S.J. Moon, R.H. Baker, P. Gao, M.K. Nazeeruddin, M. Gratzel, Sequential deposition as a route to high-performance perovskitesensitized solar cells, Nature 499 (2013) 316–319. [12] C. Huang, N. Fu, F. Liu, L. Jiang, X. Hao, H. Huang, Highly efficient perovskite solar cells with precursor composition-dependent morphology, Sol. Energy Mater. Sol. Cells 145 (2016) 231–237. [13] M. Hu, L. Liu, A. Mei, Y. Yang, T. Liu, H. Han, Efficient hole-conductor-free, fully printable mesoscopic perovskite solar cells with a broad light harvester NH2CH==NH2PbI3, J. Mater. Chem. A 2 (2014) 17115–17121. [14] J.H. Im, I.H. Jang, N. Pellet, M. Grätzel, N.G. Park, Growth of CH3NH3PbI3 cuboids with controlled size for high-efficiency perovskite solar cells, Nature Nanotechnol. 9 (2014) 927–932. [15] B.W. Park, N. Kedem, M. Kulbak, W.S. Yang, N.J. Jeon, J. Seo, G. Kim, K.J. Kim, T.J. Shin, G. Hodes, D. Cahen, Understanding how excess lead iodide precursor improves halide perovskite solar cell performance, Nature Commun. 9 (2018) 3301–3308.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Hole-conductor free ambient processed mixed halide perovskite solar cells Suresh Maniarasu, Manoj Kumar Rajbhar, Reshma K. Dileep, Easwaramoorthi Ramasamy, Ganapathy Veerappan ⇑ Centre for Solar and Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur P.O, Hyderabad 500005, India
a r t i c l e
i n f o
Article history: Received 31 December 2018 Received in revised form 6 March 2019 Accepted 7 March 2019 Available online 9 March 2019 Keywords: Perovskite solar cells Ambient processed Mixed halide perovskite Hole conductor free solar cells
a b s t r a c t In the past several years, organic-inorganic halide based perovskites has become an exciting topic in the field of photovoltaic community. Conventional perovskite solar cells (PSC) use 2,20 ,7,70 -Tetrakis[N,N-di(4methoxyphenyl)amino]-9,90 -spirobifluorene (spiro-OMeTAD) as a hole transporting layer (HTL), but the cost and stability of the polymeric HTL affects the scaling-up of PSC. This work, reports a hole- conductor free-ambient processed mixed halide PSCs with promising efficiency by tuning the morphology of the perovskite films by employing different deposition techniques (one step, two-step and dip coating method). In the dip coating method, unique cuboid structured films with good absorption and pin hole free films were obtained. The photovoltaic performances of the devices made by various deposition methods were measured at 1 sun illumination under standard conditions and achieved upto 6.5%. Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction Organic-Inorganic hybrid halide perovskite materials have been widely used in photovoltaic field due to their fascinating properties. In a short span of time, the efficiency of perovskite photovoltaic cell soared from 3.1% to 23.1% [1–3]. The instability of perovskite solar cells (PSCs) in the presence of organic hole transporting material (HTM) and cost of the metal cathode and HTM materials limits the possibilities of large scale fabrication and commercialization of PSCs. This led to the evolution of hole conductor free devices with enhanced stability [4]. Various methods are being used to enhance the performance of the PSC, which includes engineering the perovskite material by inclusion of new materials, surface engineering etc. [5,6]. Altering the lead content and inclusion of new halides tunes the electronic properties such as band gap and diffusion length of the material. Addition of PbCl2 in small quantities to MAPbI3 tunes the diffusion lengths from 100 nm to 1 mm [7]. Although, several reports are available for mixed halide perovskites for conventional PSC, but the exploration of such mixed halide perovskite in ambient processed HTM free PSCs are scarce [8]. In this letter, ambient processed mixed halide perovskite (MAPbI3xClx) films were prepared by three different depositing techniques (one step, two-step and dip coating). Organic⇑ Corresponding author. E-mail address: [email protected] (G. Veerappan). https://doi.org/10.1016/j.matlet.2019.03.021 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
Inorganic perovskite films synthesised by dip coating technique yielded highly ordered cuboid morphology compared to the one step and two step spin coating techniques [8]. This highly ordered cuboid morphology resulted in, increased current density due to improved charge carrier transport properties and lesser number of grain boundaries [8,9]. Organic-Inorganic PSC’s fabricated with these different techniques are compared and analysed.
2. Results & discussion The schematic diagram in Fig. 1 shows three different deposition techniques as described in the experimental section. To gain insight into the influence of various deposition techniques, we first investigated the phase formation and crystallinity of the samples. Fig. 2(e) shows the XRD patterns of the mixed halide perovskite (MAPbI3xClx) prepared by one step, two step and dip coating techniques and annealed at 120 °C/30 min. The diffraction peaks at 2h = 14.01°, 28.19° and 43.09°, corresponds to (1 1 0), (2 2 0) and (3 3 0) diffraction peaks of mixed halide perovskite (MAPbI3xClx) with tetragonal crystal structure [10–12]. The colour of the film varied with different deposition techniques. In spin coating, the film was transparent and slowly changes to dark brown after heating at 120 °C/30 min, but in case of dip coating, the films immediately changed to dark brown colour in fraction of seconds. Fig. S1 illustrate the typical absorption spectra of the film prepared by the different deposition techniques. The
S. Maniarasu et al. / Materials Letters 245 (2019) 226–229
227
Fig. 1. Schematics of deposition by (a) one-step (b) two-step and (c) dip coating methods.
Fig. 2. Surface Morphology of (a) pristine PbCl2 film. (b) one-step, (c) two-step, (d) dip coated perovskite film, (e) XRD patterns of MAPbI3xClx made with one step, two step and dip coating method.
band gap of this mixed halide perovskite was evaluated as 1.55 eV by the tauc plot which were similar to the reported values [13]. Effect of different deposition techniques on morphology of the films were further analysed with the help of FE-SEM images. Fig. 2 shows the surface morphology of the pristine PbCl2 film
and different deposition technique films. When PbCl2 was used over the TiO2 for the mixed halide perovskite, small granular grain morphology with proper coverage was observed. Fig. 2(b) shows surface morphology of the film prepared by 1 M of PbCl2 and 3 M of methylammonium iodide (MAI) constitutes of big grain size
228
S. Maniarasu et al. / Materials Letters 245 (2019) 226–229
Fig. 3. Current-Voltage (I-V) studies of MAPbI3xClx prepared with three different deposition techniques, (b) Internal photon conversion efficiencies of mixed halide devices.
Table 1 Photovoltaic performances of mixed halide devices fabricated with different techniques. Deposition Methods
JSC (mA/cm2)
VOC (V)
FF (%)
Η (%)
Dip Coating Two-step One-step
13.9 10.3 8.6
0.765 0.738 0.691
52.2 46.1 40.2
6.5 4.1 2.8
Where, JSC – current density; VOC – open circuit voltage; FF – fill factor and g – power conversion efficiency.
but the presence of pin holes leads to recombination of charge carriers [12]. Fig. 2(c) shows the film prepared by spin coating, which exhibits column like morphology with small pin holes. Fig. 2(d) shows the film morphology of dip coating, which was made by directly dipping the PbCl2 film into the MAI solution. According to the reported literature, the morphology of cuboids improves the light absorption and electrons could be easily transferred to the anode through the grain boundaries, which avoids the recombination of charge carriers [14]. Size of the cuboids varies as a function of dipping time and the concentration of MAI, lower concentrations can yield cuboids of size up to 1 mm [14]. These FE-SEM results confirm that dip coating yields better films and photovoltaic performance, compared to the other two techniques due to high crystallinity with large grain size [14]. Spectra in Fig. 3(a) shows the photovoltaic performances are strongly influenced by the deposition techniques and their corresponding solar cell parameters are tabulated in Table 1. Despite the complete conversion of perovskite (Fig. 2e) by one step method, the J-V parameters of the devices are poor, because of the non-uniform perovskite film, which has large pin holes and consequently increases the recombination and affects the power conversion efficiency (PCE). Whereas, the presence of excess amount of PbI2 has been observed in the perovskite film to be beneficial, but why is still unclear. The remnant PbI2 can be observed at the grain boundaries which passivates the TiO2 interface resulted in, enhanced charge transfer and less recombination. In addition, the perovskite films with small amount of excess PbI2 showed highly ordered morphology which is beneficial for photovoltaic performance [15]. Devices made with spin coating had slightly improved photovoltaic parameters, due to the column like morphology and proper coverage. Compared to the above mentioned techniques, the dip coating method shows better improvement in the current density and other parameters. The higher
current density (JSC) in dip coating method might be due to the light scattering by the cuboids, which ascribes to high absorbance and low series resistance in the device [14]. Due to the cuboid surface morphology, it yields good absorption and pin hole free film yielding such high current and efficiency. The high quality films helps in reducing the recombination of charge carriers, the strong interfaces help in better charge extraction leading to enhanced voltage and current density. Larger cuboid perovskites employed PSCs exhibit a higher fill factor due to the less number of grain boundaries, reducing the charge transfer resistance and the series resistance compared to the perovskite films developed by other two techniques resulting in enhanced fill factor [14]. Fig. 3b shows the external quantum efficiency of the mixed halide perovskite for three deposition techniques. The internal photon conversion efficiency (IPCE) spectra of the solar cell fabricated by one step method were lower when compared with the other two techniques due to non-uniform film morphology. Due to the better surface morphology, the device prepared by spin coating shows good photon conversion compared to the one step technique. The device fabricated by dip coating technique has harvested more than 60% of the incident photons because of the cubic structured morphology, which increases the light absorption range resulting in excellent charge transport to electrodes [13]. The IPCE spectrum of these devices is similar to their absorption spectra (i.e. more absorption in the range of 380 nm–520 nm). Low response of the IPCE spectrum in the wavelength range of 550 nm–750 nm is due the absorption of lead iodide or recombination of some low energy photons in HTM free devices. The integrated JSC value calculated from the IPCE spectra, which is slightly lower than the values obtained from the IV characteristics for all three deposition techniques.
3. Conclusion We studied the influence of mixed halide perovskite by different deposition techniques and its photovoltaic performance on hole conductor free PSC’s fabricated under ambient conditions. Cuboidal nanostructured mixed halide films were yielded by dip coating method, which has high uniformity, pin hole free and large grain size. The cuboidal structured perovskite film results in a low resistance and better performing devices with high fill factor, JSC and open circuit voltage (VOC) when compared with the other devices. With further optimization, PCE of these devices can be doubled.
S. Maniarasu et al. / Materials Letters 245 (2019) 226–229
Conflicts of interest None Acknowledgments Dr. G. V acknowledges the Department of Science and Technology, New Delhi, India for the financial support through DSTINSPIRE Faculty award (IFA 14-MS-28), DST-SYST (SP/ YO/012/2017 (G)) and TRC (AI/1/65/ARCI/2014). G. V. and coauthors extend their acknowledgment to the Director, ARCI. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.03.021. References: [1] M. Wright, A. Uddin, Organic – inorganic hybrid solar cells: a comparative review, Sol. Energy Mater. Sol. Cells 107 (2012) 87–111. [2] S. Maniarasu, T.B. Korukonda, V. Manjunath, M. Ramesh, G. Veerappan, E. Ramasamy, Recent advancement in metal cathode and hole-conductor-free perovskite solar cells for low-cost and high stability: a route towards commercialization, Renew. Sustain. Energy Rev. 82 (2017) 845–857. [3] https://www.nrel.gov/ncpv/images/efficiency_chart.jpg. [4] H.S. Kim, C.R. Lee, J.H. Im, K.B. Lee, T. Moehl, A. Marchioro, S.J. Moon, R. Humphry-Baker, J.H. Yum, J.E. Moser, M. Gratzel, N.G. Park, Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9%, Sci. Rep. 2 (2012) 591–597.
229
[5] J.-F. Wang, L. Zhu, B.-G. Zhao, Y.-L. Zhao, Y.-L. Zhao, X.-Q. Gu, Y.-H. Qiang, Surface engineering of perovskite films for efficient solar cells, Sci. Rep. 7 (14478) (2017) 1–9. [6] V.L. Pool, A. Gold-Parker, M.D. McGehee, M.F. Toney, Chlorine in PbCl2-derived hybrid-perovskite solar absorbers, Chem. Mater. 27 (2015) 7240–7243. [7] N.D. Pham, V.T. Tiong, P. Chen, L. Wang, G.J. Wilson, J. Bella, H. Wang, Enhanced perovskite electronic properties via a modified lead(II) chloride Lewis acid– base adduct and their effect in high-efficiency perovskite solar cells, J. Mater. Chem. A 5 (2017) 5195–5203. [8] P. Docampo, F. Hanusch, S.D. Stranks, M. Döblinger, J.M. Feckl, M. Ehrensperger, N.K. Minar, M.B. Johnston, H.J. Snaith, T. Bein, Solution deposition-conversion for planar heterojunction mixed halide perovskite solar cells, Adv. Energy Mater. 1400355 (2014) 1–5. [9] S.T. Williams, F. Zuo, C.C. Chueh, C.Y. Liao, P.W. Liang, A.K.Y. Jen, Role of chloride in the morphological evolution of organo-lead halide perovskite thin films, J. Am. Chem. Soc. 8 (2014) 10640–10654. [10] J. Liu, J. Lin, Q. Xue, Q. Ye, X. He, L. Ouyang, D. Zhuang, C. Liao, H.L. Yip, J. Mei, W.M. Lau, Growth and evolution of solution-processed CH3NH3PbI3-xClx layer for highly efficient planar-heterojunction perovskite solar cells, J. Power Sources 301 (2016) 242–250. [11] J. Burschka, N. Pellet, S.J. Moon, R.H. Baker, P. Gao, M.K. Nazeeruddin, M. Gratzel, Sequential deposition as a route to high-performance perovskitesensitized solar cells, Nature 499 (2013) 316–319. [12] C. Huang, N. Fu, F. Liu, L. Jiang, X. Hao, H. Huang, Highly efficient perovskite solar cells with precursor composition-dependent morphology, Sol. Energy Mater. Sol. Cells 145 (2016) 231–237. [13] M. Hu, L. Liu, A. Mei, Y. Yang, T. Liu, H. Han, Efficient hole-conductor-free, fully printable mesoscopic perovskite solar cells with a broad light harvester NH2CH==NH2PbI3, J. Mater. Chem. A 2 (2014) 17115–17121. [14] J.H. Im, I.H. Jang, N. Pellet, M. Grätzel, N.G. Park, Growth of CH3NH3PbI3 cuboids with controlled size for high-efficiency perovskite solar cells, Nature Nanotechnol. 9 (2014) 927–932. [15] B.W. Park, N. Kedem, M. Kulbak, W.S. Yang, N.J. Jeon, J. Seo, G. Kim, K.J. Kim, T.J. Shin, G. Hodes, D. Cahen, Understanding how excess lead iodide precursor improves halide perovskite solar cell performance, Nature Commun. 9 (2018) 3301–3308.