Behavior of cigs absorber layer of solar cells against to radiation

Along with the development of technology, the increase in energy demand has increased the interest in alternative energy sources. The p-type chalcopyrite CIGS thin-film solar cells belong to alternative energy sources are devices that convert photon energy into electrical energy through photovoltaic energy conversion. Chalcopyrite copper indium gallium (di)selenide-Cu(In,Ga)Se2 (CIGS) thin films are good canditates for thin film solar cell applications due to high absorption coefficient ( >105 cm−1). CIGS thin films have direct band gap and tunable energy band gap that can be changed from 1.0 eV to 1.7 eV by increasing the gallium amount of the absorber. CIGS thin film solar cells have high conversion efficiency among all thin-film polycrystalline solar cells. 21% efficiency has been reported for Cu(In,Ga)Se2 (CIGS) and CdTe. The highest confirmed 'one sun' cell and module results measured under the global AM 1.5 spectrum (1000 Wm−2 at 25°C (IEC 60904-3: 2008, ASTM G-173-03 global for CIGS thin film solar cell efficiency is 22.3%, Voc is 0.4219 V, short-circuit current density (Jsc is 39.38 mA/cm2 and the FF is 78.2%. In the literature, the CIGS absorber layer can be produced by many different methods, such as high vacuum thermal evaporation, pulsed electron growth, metalorganic chemical vapor deposition (MOCVD), molecular beam molecular beam epitaxy (MBE), and pulsed laser magnification (PLD). However, in this study, CIGS thin films were economically deposited by sol-gel dip coating technique using a different and unique recipe, which is not described in detail in the literature. In this thesis, CIGS thin films were grown at different annealing times, at different thicknesses, at different at.%SeO2 concentration, at different dipping rates and at different selenium source. XRD, SEM, FTIR, XRF, AFM, UV Visible Region Spectroscopy PL and 4 point pobe resistivity measurements are performed to characterize the CIGS thin films showing the best structural, optical and electrical properties. In addition, CIGS thin films were exposed to reactor neutrons and Co-60 radioisotope and their behavior against ionizing radiation was tested and the changes in their electrical properties were investigated to increase their use in aerospace and space technology applications. In the first part of this doctoral dissertation study, the CIGS solution was synthesized using the SeO2 compound as a selenium source to grow ultra-thin CIGS thin films. First, thin films were annealed at 200°C for four different durations (15, 30, 45 and 60 min) in order to investigate the effect of annealing time on the crystallite structure in CIGS thin films prepared by using the sol-gel dip coating technique. CIGS thin films annealed at 200°C for 60 min have been found to have the best structural and optical properties. In the second part of this thesis study, CIGS solution was synthesized at different SeO2 at.% concentrations. It was determined that the optimum selenium concentration in the production of CIGS thin film by using the sol-gel method, was at at.%20,22 SeO2, but it was preferred to use at at.50% SeO2 concentration, depending on the development of CIGS thin films after neutron exposure. In our third study, structural, optical, and electrical properties of CIGS thin films fabricated on soda-lime silicate glass substrates using a layer-by-layer sol-gel dip-coating method was investigated at different dipping numbers. It was determined that the CIGS thin films (thickness 300 nm), dipped 11 times, gave the best optical absorption due to the optical reflection at the surface of film. In addition, the electrical conductivity of CIGS thin films formed in these production parameters was found to be increased due to the reduction of electrical resistance. In another part of this thesis, CIGS thin films were grown by changing the dipping speed during sol-gel dip coating technique and CIGS thin films were prepared by dipping at 200 mm/dk. dipping rate exhibited the best optical and structural properties. In the next sections of our study, the CIGS thin films, synthesized at different at.% SeO2 concentrations and annealed at different annealing times, were exposed to neutrons in the processing with reactor neutrons. It has been determined that the CIGS thin films prepared at a at.50% SeO2 concentration and annealed at 200°C during 60 min exposed to reactor neutrons exhibit the best structural, optical and electrical properties. The at.% SeO2 ratio in the structure increased, due to their interactions with neutrons resulting in the decrease of optical transmittance and reflectance leads to an increase in the absorbance and electrical conductivity. In addition, CIGS thin films coated at different thicknesses were exposed to Co-60 gamma radioisotope, and the changes in the structural, optical and electrical properties were investigated at three different doses. The optical reflectance and transmittance properties of the CIGS thin films irradiated by Co-60 radioisotope films, decreased and the optical absorbance increased due to the effect of ionizing radiation. It was determined that the films exposed to three different doses of gamma rays such as 0.02, 0.03 and 0.05 Gy, were improved in terms of optical and electrical properties. It has been determined that CIGS thin films exposed to Co-60 gamma radioisotope at a dose of 0.05 Gy, coated with 11 layers exhibit the best crystalline structure, optical and electrical properties. It has been found that the increasing of the deposited layer and exposed to gamma rays, increase the gamma radiation attenuation coefficient by increasing the number of film layers while decreasing the surface electrical resistance. The gamma radiation linear attenuation coefficient has been found to increase due to the increase in the duration of the annealing being exposed and partly due to increased bulk density. Therefore, the linear attenuation coefficient for gamma radiation was evaluated at two different gamma photon energies, namely, 0.662 MeV (emmited from Cs-137 radioisotope) and ~ 1.25 MeV (emmited from Co-60 radioisotopes). In the gamma transmission technique tests using both the Cs-137 and Co-60 radioisotope, the highest linear attenuation coefficient was performed at irradiated (0.05 Gy) 11-layer deposited CIGS thin films. The irradiation process and the increase of thickness of CIGS thin films caused a higher linear attenuation coefficient, higher absorption and improvement in electrical conductivity. The increase of the linear attenuation coefficient indicated the rise of the density of the irradiated CIGS thin film, due to the improvement of the grains of the irradiated thin films. The irradiation effect on CIGS thin films was thus investigated in order to examine modifications induced by the cumulative dose of gamma radiation. CIGS thin film solar cells are produced using a practical method that includes the element of powder Se as a Se source.in a CIGS solution. CIGS thin films have been made suitable for use as a p-type absorber layer in the chalcopyrite structure.The CdS layer used as n-type buffer layer in CIGS thin-film solar cells, with a forbidden energy bant gap of 2.3 eV was grown by chemical bath deposition method. The transparent ZnO: Al layer coated on CdS was produced at the forbidden energy bant gap of 3.2 eV using the sol-gel dip coating technique. The optical and structural properties exhibit that CIGS thin is crystallized in the well known chalcopyrite structure and the energy bant gap of the CIGS thin film, CdS and the ZnO:Al similar with the literatüre. The CIGS thin film that derived by sol-gel technique was suitable to obtain an absorber layer for the use in high efficiency thin film solar cells at the Al/ZnO:Al/CdS/CIGS/Mo/ SLSG configuration. Also it can be used as a diode for electrical applications. The I–V characteristics of the CIGS based solar cells under UV light(100 mW/cm2) and in the dark exhibit the ideality factor n=1.5 for under UV light, n=33.78. dark current. It has been determined that the value of the ideal factor of the CIGS decay is lower than the dark current value under UV light. The improvement of the optical and electrical properties of irradiated CIGS thin films was investigated in order to evaluate their utility as an absorber layer in solar cell applications for aerospace technology. A suitable sol-gel CIGS solutionwas developed in order to determine the effects of irradiation on CIGS thin films. The CIGS thin film with 11 layers (thickness ~ 300 nm) exhibited the best optical absorbance, with decreasing reflectance and electrical resistivity on the surface of the thin films. The development of graininess in CIGS thin films irradiated by the Co-60 radioisotope resulted in the improvement of optical absorbance. The enhancement of the grainy nature of the irradiated CIGS thin films caused a decrease of the reflectance of the thin films. The increase of surface roughness led to the decrease of optical transmittance along with the decrease of reflectance. Additionally, the improvement of crystallinity due to the ordering of the sublattice of Cu and In atoms also resulted in the decrease of the electrical resistivity after irradiation at 0.05 Gy. The improvement of grains in the irradiated CIGS thin films resulted in the increase of the gamma attenuation coefficient with the decrease of electrical resistivity. Therefore, the linear attenuation coefficient for gamma radiation was evaluated at two different gamma photon energies, namely, 0.662 MeV (emmited from Cs-137 radioisotope) and ~1.25 MeV (emmited from Co-60 radioisotopes). Irradiation with gamma rays led to the increase of the linear attenuation coefficient of the CIGS thin films. The increase of the linear attenuation coefficient indicated the rise of the density of the irradiated CIGS thin film, due to the improvement of the grains of the irradiated thin films. The irradiation effect on CIGS thin films was thus investigated in order to examine modifications induced by the cumulative dose of gamma radiation. These results are pertinent for applications of these materials in high-altitude flight operations. As a result of all these studies, CIGS thin films were prepared by using sol–gel dip coating method on Mo coated soda-lime-silicate glass (SLSG). The solution was produced by using a practical method containing trioctylphosphine to provide some progress on scientific and industrial innovation on preparation of CIGS solution for the use in CIGS thin film solar cells. The n-type transparent conductive ZnO:Al thin film layer was deposited by sol–gel dip coating technique too. The buffer layer CdS is deposited by chemical bath deposition. Hence, the CIGS solar cell with the Al/ZnO:Al/CdS/CIGS/Mo/SLSG configuration was fabricated with the economical and more eco-friendly technique. The optical and structural properties exhibit that CIGS thin is crystallized in the well known chalcopyrite structure and the energy band gap of the CIGS thin film, CdS and the ZnO:Al similar with the literature. The I–V characteristics of the CIGS based solar cells exhibited the diode properties with the solar efficiency ∼0.2%. The ideality factor is found to less for the CIGS/CdS/Zno:Al heterojunction under UV light (n =1.5) than the dark current (33.78) because of the recombination within the material. The CIGS thin film that derived by sol–gel technique was suitable to obtain an absorber layer for the use in high efficiency thin film solar cells at the Al/ZnO:Al/CdS/CIGS/Mo/ SLSG configuration. Also it can be used as a diode for electrical applications.