Fast processed crystalline methyl violet-6B thin films for optimizing the light-harvesting characteristics of Ag/methyl violet 6B/p-Si/Al solar cells

Abstract

In the present work, fabrication of crystalline methyl violet 6B thin films with thickness ranging from 95 to 237 nm was aimed and revealed the thermal post-annealing roles (373 K) of structural and optical properties of these films prior to fabrication of Ag/MV-6B/p-Si/Al heterojunctions solar cells. As-grown samples revealed textured films with crystalline granular particles and the other annealed films had a smoothed and healed surface embedded by small crystalline cubes. The crystal structure of methyl violet 6B was analyzed in powder form by X-ray diffraction (XRD) and exhibits triclinic unit cell: a = 7.0695 Å, b = 11.9807 Å, c = 15.8710 Å, α = 64.02 Å, β = 67.67 Å and γ=83.81 Å, and space group (P1). The average crystallite size of plane [011] for methyl violet 6B in powder form and as-grown and annealed film forms is 27, 23 and 32 nm, respectively. All fabricated MV-6B films have a transparency not less than 80% in the range of the IR region. The evaluated transition is allowed one and the calculated onset optical gap is 1.766 and 1.643 eV for as-grown and annealed films, respectively. There was an abrupt change in the value of skin depth, δο, from 5.76 × 10−4 cm to nearly 0 as the photon energy was increased from 1.92 to 2.3 eV. This result may be important in optical switching applications. The calculated static dielectric constant was εst = no2 which was found to be 1.807 and 1.821 for as-grown and annealed films, respectively. Spin-coated nanocrystalline MV-6B films were successfully utilized to fabricate Ag/MV-6B/p-Si/Al heterojunctions. The thermal annealing at 373 K decreased the barrier height of the fabricated heterojunctions from 0.77 for as-grown to 0.663 eV. The annealing temperature improved the responsivity of the Ag/MV-6B/p-Si/Al devices. The series resistance of the junction was decreased from 345 to 202 Ω, but the saturation current was increased from 67 nA to 0.55 µA for as-grown and annealed MV-6B/p-Si junctions, respectively. The power conversion efficiency (PCE) of Ag/MV-6B/p-Si/Al heterojunctions was increased from 1.36 to 3.61% with the incident light intensity from 31 to 90 mW/cm2.