Novel and Proficient Organic-Inorganic Lead Bromide Perovskite for Solid-State Solar Cells

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Novel and Proficient Organic-Inorganic Lead Bromide Perovskite for SolidState Solar Cells 1

B. Praveen1, Tenzin Tenkyong1, W. Jothi Jeyarani1, J. Sahaya Selva Mary1, V.Chandrakala1, Neena Bachan1, J. Merline Shyla1,a 1 – Department of Physics, Energy NanoTechnology Centre (ENTeC), Loyola Institute of Frontier Energy (LIFE), Loyola College, Chennai, India a – jmshyla@gmail.com DOI 10.2412/mmse.24.90.160 provided by Seo4U.link

Keywords: perovskite, spin coating, photoconductivity, solid-state solar cells.

ABSTRACT. Efficient solar cells based on organic/inorganic lead halide perovskite absorbers which are emerging recently, assure the renovation in the fields of dye sensitized, organic and thin film solar cells, whose performance are reported to have exceeded ~ 24% power conversion efficiency. Here, we report the synthesis and fabrication of a novel and proficient perovskite material prepared by spin coating technique using methyl ammonium lead bromide (CH3NH3PbBr3). Several characterization techniques such as Ultraviolet–Visible Diffuse Reflectance Spectroscopy (UVDRS), Fourier Transformer Infra-Red (FTIR) analysis, X-Ray Diffraction (XRD) analysis and Field dependent dark and photoconductivity are to be done to analyze the behavior of the perovskite material. The X-ray diffraction pattern reveals the composition of the materials present in the sample. UV-visible analysis showed an enhanced absorption of the perovskite material and the photoconductivity techniques revealed the ohmic nature of the samples with a linear increase in both dark and photocurrent with corresponding increase in the applied field. Thus, these novel and proficient perovskite materials could overcome the limitations of existing perovskites and lead to higher performance in solid-state solar cells.

Introduction. Efficient and economical energy harvesting by solar cells is a great challenge for the 21st century in the field of key technology for sustainable energy supply. Most recently, inorganic– organic hybrid perovskite materials have been widely fabricated and rapidly demonstrated in the most promising emerging photovoltaic devices with respect to increase in efficiency[1-2]. Perovskite is a material with a specific crystal structure named after the Russian mineralogist L. A. Perovski [3].

Inorganic-organic perovskite materials taking the form ABX3 (A = CH3NH3+; B = Pb+; and X=Cl–, I–, Br–) has with in the past 4 years been used to fabricate high-performance hybrid solar cells, with reported power conversion efficiencies (ƞ) >25 % [4]. An organo-lead halide perovskite based solar cell which requires charge separation (electrons and holes) and less recombination in a light absorbing material to transmit electricity for photovoltaic applications [5].

In the present work, the CH3NH3PbBr3 perovskite material has been synthesized and fabricated by using the spin coating method. The perovskite sensitizer has high light absorption coefficient [6], [7] which would aid in increasing the light harvesting ability of the sensitized material.

Experimental Section Perovskite (CH3NH3PbBr3) synthesis. The perovskite solution was synthesised as described in the Fig 1. Initially Methylammonium Bromide (CH3NH3Br) precursor solution was synthesized by reacting 30 mL of hydrobromide acid and 23 mL of methylamine at 0oC for 2 h with continuous stirring. The precipitate was recovered by evaporating at 50°C for 1 h. The product is washed (using funnel and filter paper) three times with di-ethyl ether or one time with ethanol and finally dried at 60°C for 24 h. An amount of 0.369g of prepared CH3NH3Br solution was added to 1.157g of PbBr2 1

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

(lead bromide) in 2 mL of dimethyl formamide and was kept at 60°C for 12 h to obtain the final solution [8].

Fig. 1. Schematic representation for CH3NH3PbBr3 Perovskite.

Fabrication of perovskite material. The final process involved in the completion of the procedure is the fabrication of the perovskite solution onto the ITO substrate by spin coating at 3000 rpm for 30 sec. It is followed by drying the perovskite coated substrate by placing it on hot plate at 100oC for 5 min to complete the fabrication process [9].

Characterization. To investigate the crystallinity of the film, X-Ray Diffraction (XRD) technique was adopted employing Rigaku (Japan) diffractometer using Cu Kα as a radiation source at 9 kW having wavelength of 1.5405 Å. The optical absorption properties were measured in the range 200600 nm using CARY 5E UV–Vis–NIR spectrophotometer. The Fourier Transform Infrared spectra of the samples were studied using Perkin-Elmer infrared spectrophotometer and the spectrum was recorded in the wavenumber range of 500 to 4000 cm-1.The field dependent dark and photoconductivity of the material was done using a Keithley pico-ammeter 6485 and constant voltage source.

Results and Discussion XRD analysis

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Fig. 2. The XRD diffraction pattern of the CH3NH3PbBr3perovskite.

Figure 2 represents the phase structure of the perovskite materials. The plane values in the XRD pattern represented by (001), (011), (022), (012), (112), (022), (122), (013) (PDF#01-076-2758) [10] and intense peaks at 14.96°, 21.20°, 30.21°, 33.84°, 37.12°, 43.24°, 45.96° and 48.64° could be correlated to the crystalline nature of the perovskite sample [11].

UV-Vis Absorption Spectroscopy.

a)

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b) Fig. 3. (a)The UV-Vis absorption spectra and (b) the diffuse reflectance spectra of the CH3NH3PbBr3 perovskite.

Fig. 4. The Kubelka-Munk plot of CH3NH3PbBr3 perovskite.

Figure 3 (a) showing the absorption spectrum obtained through diffuse reflectance technique indicated a red shift in the range of 300-600 nm for the CH3NH3PbBr3 perovskite confirming its photo response in the visible region [10], [13]. Figure 3(b) showed the UV–Vis diffuse reflectance spectrum of the CH3NH3PbBr3 perovskite and evidenced its light scattering ability. The enhanced light scattering could confine the incident light in CH3NH3PbBr3 perovskite and thus play a significant role in improving the light-harvesting efficiency. Therefore the determined higher photocurrent of CH3NH3PbBr3 perovskite can be partially attributed to the enhanced light scattering effect in the longwavelength region [14].

Figure 4 shows that the Kubelka-Munk (K-M) plot [hν-(R)2] vs hν (eV) of CH3NH3PbBr3 perovskite was used to estimate its direct bandgap energy as 2.2 eV [15].

FTIR Analysis. Figure 5 shows the Fourier transform infrared spectrum of theCH3NH3PbBr3 perovskite sample. The normal modes with frequencies between 500 and 4000 cm-1 are exclusively MMSE Journal. Open Access www.mmse.xyz

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

internal vibrations of the MA cations, i.e., torsion, stretching, and bending modes of the C− H, N−H, and C−N bonds [16].

Fig. 5.The FTIR spectrum of CH3NH3PbBr3 perovskite.

The three strong bands observed at 3483, 2422 and 1679 cm-1 were associated with degeneracy and symmetric NH3+ stretching vibrations [17]. The characteristic absorption peaks at 1523, 1132 and 619 cm-1 confirmed the CH3, C-C symmetric stretching and (C-Br) strong stretching vibrations respectively [18].

Field Dependent Dark and Photocurrent

Fig. 6. The field dependent dark and photocurrent ofCH3NH3PbBr3perovskite.

The plots indicated a linear increase of current in both dark and visible light-illuminated conditions [19]. Further, photocurrent was found to be significantly higher than the dark current thereby suggesting a strong photoresponse in the CH3NH3PbBr3 perovskite material [20].

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Summary Perovskite-type CH3NH3PbBr3 compounds possessing cubic and tetragonal crystal structures were synthesized and characterized with X-ray diffraction parameters. UV-visible analysis showed an enhanced absorption of the perovskite material and the photoconductivity studies suggested the ohmic nature of the samples with a linear increase in both dark and photocurrent with corresponding increase in the applied field. Reflectance measurements using integrating sphere provide the absorption coeffcient of the hybrid structures that assist in calculating the band gap of 2.2 eV. Therefore, high-efficiency CH3NH3PbBr3 perovskite material with several advantages such as lower cost, long-term stability, and simple structure would lead to improved performance in solar cells.

Acknowledgement. This work was partially funded by the Loyola College Times of India Research Grants (6LCTOI1421F002) and the authors acknowledge the same.

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