ئەز   Haveen Ahmed Mustafa

Abstract Spin coating is a technique employed for the deposition of uniform thin films of organic materials in the range of micrometer to nanometer on flat substrates. Typically, a small amount of coating material generally as a liquid is dropped over the substrate center, which is either static or spinning at low speed. The substrate is then rotated at the desired speed and the coating material has been spread by centrifugal force. A device that is used for spin coating is termed a spin coater or just a spinner. The substrate continued to spin and the fluid spins off the boundaries of the substrate until the film is reached the required thickness. The thickness and the characteristics of coated layer (film) are depending on the number of rotations per minute (rpm) and the time of rotation. Therefore, a mathematical model is obtained to clarify the prevalent method controlling thin film fabrication. Viscosity and the concentration of (solution) spin coating material are also affecting the thickness of the substrate. This article reviews spin coating techniques including stages in the coating process such as deposition, spin-up, stable fluid outflow (spin-off), and evaporation. Additionally, the main affecting factors on the film thickness in the coating process are reviewed.

Abstract This paper reports the fabrication and electrical characterization of hybrid organic-inorganic solar cell based on deposition of polyaniline (PANI) on n-type GaAs substrate with three different crystal orientations namely Au/PANI/(100) n-GaAs/(Ni-Au), Au/PANI/(110) n-GaAs/(Ni-Au), and Au/PANI/(311)B n-GaAs/(Ni-Au) using spin coating technique. The effect of crystallographic orientation of n-GaAs on solar cell efficiency of the hybrid solar cell devices has been studied utilizing current density-voltage (J-V) measurements under illumination conditions. Additionally, the influence of planes of n-GaAs on the diode parameters of the same devices have been investigated by employing current-voltage (I-V) characteristics in the dark conditions at room temperature. The experimental observations showed that the best performance were obtained for solar cell fabricated with the structure of Au/PANI/(311)B n-GaAs/(Ni-Au). The open circuit voltage (Voc), short circuit current density (Jsc) and solar cell efficiency (η) of the same device were shown the values of 342 mV, 0.294 mAcm-2, 0.0196%, respectively under illuminated condition. All the solar cell characteristics were carried out under standard AM 1.5 at room temperature. Also, diode parameters of PANI/(311)B n-GaAs heterostructures were calculated from the dark I-V measurements have revealed the lower reverse saturation current (Is) of 3.0×10-9 A, higher barrier height (ϕ_b0) of 0.79 eV and lower ideality factor (n) of 3.16.