Three demonstration samples of intrinsic hydrogenated amorphous silicon (a-Si:H) films were deposited using hot wire-chemical vapour deposition (HW-CVD) technique. The optical parameters and the thickness were determined from the extremes of the interference fringes of transmission spectrum in the range of 400-2500 nm using the envelope method. The calculated values of the refractive index (n) were fitted using the two-term Cauchy dispersion relation and the static refractive index values (n 0 ) obtained were 2.799, 2.629 and 3.043 which were in the range of the reported values. The calculated thicknesses for all samples were cross-checked with Taly-Step profilometer and found to be almost equal. Detailed analysis was carried out to obtain the optical band gap (E g ) using Tauc's method and the estimated values were 1.99, 2.01 and 1.75 eV. The optical band gap values were correlated with the hydrogen content (C H ) in the samples calculated from Fourier transform infrared (FTIR) analysis. An attempt was made to apply Wemple-DiDomenico single-effective oscillator model to the a-Si:H samples to calculate the optical parameters. The optical band gap obtained by Tauc's method and the static refractive index calculated from Cauchy fitting are in good agreement with those obtained by the single-effective oscillator model. The real and the imaginary parts of dielectric constant (ε r , ε i ), and the optical conductivity (σ ) were also calculated.
Hybrid lead halide perovskites have emerged as an attractive photoactive semiconductor for optoelectronic applications such as photovoltaics. However, their toxicity and stability issues pose significant challenges to its wide-scale applications and hence the need to find alternative perovskites that are stable and environmentally benign. Recently, double perovskites have been suggested as a potential alternative owing to their non-toxicity and high stability. In the present study, we report the first synthesis of Rb2AgBiI6 thin films in a cubic crystal structure using a facile room-temperature single-step solution process synthesis method and explore their potential optoelectronic applications. The structural, thermal, and mechanical stability, electronic, and optical properties are studied using various experimental techniques, and the results are further corroborated by first-principles density functional theory (DFT) calculations. The Rb2AgBiI6 film has an estimated band gap ∼ of 1.98 eV with the demonstrated thermal stability of ∼ 440 o C, suggesting its potential suitability for low-cost thin-film solar cells. The initial fabricated photovoltaic device without optimization of the synthesis conditions and device architecture show power conversion efficiency (PCE) of 0.1 % and an open-circuit voltage (Voc) of 0.46 V. The successful incorporation of Rb in Bi-based double perovskite should open the way to a new class of Rubidium-based perovskites with significant potential for optoelectronic applications.
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