Effect of Gd 3+ doping on structural, morphological, optical, dielectric, and nonlinear optical properties of high-quali

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EffectofGd3+ dopingonstructural,morphological,optical, dielectric, and nonlinear optical properties of high-quality PbI2 thin films for optoelectronic applications Mohd. Shkir1

Salem AlFaify1,a)

1

Advanced Functional Materials & Optoelectronics Laboratory (AFMOL), Department of Physics, College of Science, King Khalid University, Abha 61413, Saudi Arabia a) Address all correspondence to this author. e-mail: [email protected] Received: 14 February 2019; accepted: 19 March 2019

Herein, we present the fabrication and characterization of Gd:PbI2 thin films from low-cost material using a cost-effective spin-coating technique by taking the Gd content as 1.0, 2.0, and 3.0 wt% in PbI2. Single-phase and good crystallinity films oriented along the c-axis were confirmed by X-ray diffraction and FT-Raman spectroscopy. Size of crystallites increased with Gd concentration and was estimated to be in the range of 16– 32 nm. Determination of morphology and size of grains (50–103 nm), and elemental confirmation were carried out by SEM/EDX analysis. Optical transparency of fabricated films was found to be in the range of 72–92%. The energy gap is reduced from 2.31 to 2.05 eV; this makes Gd:PbI2 films highly applicable in solar cells. The stable value of refractive index is estimated to be in the range of 1.85–2.3. Dielectric constant was observed to be reduced with doping and in the range of 2.5–35, and ac conductivity was also reduced by doping; however, both were enhanced with frequency. The values of v(1), v(3), and n(2) are found to be in the range of 0.15 to 2.5, 8 × 1014 to 6.5 × 10−9, and 5 × 10−12 to 4 × 10−8, respectively.

Introduction Tremendous applications of lead iodide (PbI2) in various fields of advanced technology [1, 2, 3, 4, 5] encouraged us to further investigate PbI2. PbI2 has been highly used as a photodetector and a precursor for high-efficiency (i.e., 21%) perovskite solar cell development, and in medical imaging, radiation detection at 300 K, lasers, etc. [1, 2, 4, 6, 7, 8, 9]. According to the available literature, in the past few decades the research and development on pure and doped PbI2 thin films is quite limited. In previous reports, films of pure PbI2 are fabricated by spray pyrolysis [10, 11], solution evaporation [12], electrochemical deposition [13], pulsed laser deposition [14], flash evaporation [15], chemical vapor deposition [16, 17], close space deposition [18], and thermal evaporation/vacuum sublimation [19, 20, 21]. Xiao et al. fabricated the absorbing layer of PbI2 by spin coating for perovskite solar cell applications [22]. Recently Wang et al. reported a nanoparticles-induced pinhole-few PbI2 film for solar cells [23]. Only reports on doped PbI2 thin films exist in the literature: e.g., preparation of Ag:PbI2 films by melting and

ª Materials Research Society 2019

determination of hole conductivity [24]; Bhavsar et al. prepared Al/Cu/Zn:PbI2 films by thermal evaporation and studied their structural and optical properties [25, 26]. Most of the reports suggest that it is not easy to prepare good qu

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