Material and device characterization of ZnİnSe2 and Cu0.5Ag0.5İnSe2 thin films for photovoltaic applications

Güllü, Hasan Hüseyin
In this work, material and device characterization of n-type ZnInSe2 (ZIS) and p-type Cu0.5Ag0.5InSe2 (CAIS) polycrystalline thin films were investigated under the aim of possible photovoltaic applications. ZIS polycrystalline structure is a ternary chalcopyrite semiconductor belongs to the group of II-III-VI compounds with the interest of II-VI binary analog of ZnSe structure. Similar to its binary analogs, it has a high band gap value, however low resistivity values compared to ZnSe structure, so that it can be promising material as a window layer. On the other hand, CAIS polycrystalline thin film structure belongs to quaternary chalcopyrite semiconductor compounds and contains both of the elements in the CuInSe2 (CIS) and AgInSe2 (AIS) ternary chalcopyrite structures. Therefore, it is expected to have a similar characteristics with them, such as direct band gap, and high absorption coefficients. This indicates that it can be suitable to use as an absorber layer in the photovoltaic applications. Under the aim of material characterization of these thin film layers, they were deposited on soda lime glass substrates with the evaporation of pure elemental sources by using physical thermal evaporation technique. During the deposition process, the substrate temperature was kept at about 200 °C. The thin films were characterized firstly in as-grown form, and then annealed under the nitrogen environment to deduce the effects of annealing on the structural, electrical and optical properties of the deposited thin films. In addition to this, diode behaviors and basic diode parameters of these films were characterized. The heterostructure was produced by depositing the films on the Si-wafer having appropriate conductivity type. After completing all material and device characterization steps, as a final aim, ITO/n-ZIS/p-CAIS/In hetero-structure were fabricated as a solar cell application of the combination of these film structures. Detailed electrical characterization of this hetero-junction was performed by the help of temperature dependent current-voltage (I-V) and frequency dependent capacitance-voltage (C-V) measurements to investigate the device characteristics and to determine dominant conduction mechanism in this sandwich structure. Wavelength dependent I-V measurements were also performed to investigate the photo-transport properties. To determine photo-spectral working range of the junction, the spectral photo-response measurements were carried out in the spectral range of 300-1200 nm. This measurement was also performed in order to see the effects and contributions of the film layers on this device structure. Moreover, at room temperature, the photovoltaic characteristics of the deposited hetero-junction were investigated under different illumination intensities varying in between 20 to 115 mW/cm2.
Citation Formats
H. H. Güllü, “Material and device characterization of ZnİnSe2 and Cu0.5Ag0.5İnSe2 thin films for photovoltaic applications,” Ph.D. - Doctoral Program, Middle East Technical University, 2016.