Integration of sol-gel derived doped zinc oxide films and solution-processed metal nanoparticles for thin film photodiode and solar cell applications

The thesis work aimed at deposition, characterization, and optimization of sol-gel- derived undoped ZnO, Al-doped ZnO (AZO) and Ga-doped ZnO (GZO) thin films with emphasizing on GZO films. The films were successfully deposited on glass substrates using spin coating technique and their optical and electrical properties were optimized in order to be eligible for optoelectronic devices applications. By the deposition of GZO films on p-Si substrate, p-n heterojunctions (GZO/p-Si) were successfully formed and GZO/p-Si based optoelectronic devices were fabricated and optimized. The enhancement potential in the optical response of GZO/p-Si devices via metal nanoparticles (NPs) was investigated by spin-coating of solution-processed 100 nm size Ag and Au NPs on GZO layer. The structural, surface morphological, optical, and electrical properties of the deposited ZnO thin films were investigated using x-ray diffractometer (XRD) and scanning electron microscope (SEM), atomic force microscopy (AFM), UV-vis spectroscopy, and the four-point probe and Hall effect measurement systems, respectively. The ratio of the electrical conductivity to the absorption coefficient was used as a figure of merit (FOM) for evaluating the quality of films. FOM value of ~1.6x10-5 -1 was measured for the deposited AZO and GZO thin films. The performance of GZO/p-Si devices were analyzed from the current-voltage (I-V) characteristics measured in the dark and under AM1.5 and UV illumination conditions. Compared to literature, excellent rectification behavior, high photoresponsivity and competitive photovoltaic property were exhibited by the devices. The inclusion of Au and Ag metal NPs into the devices led to enhanced optical absorption and consequently improved the performance of the devices in terms of photoelectric properties.