Fabrication of doped zinc oxide thin films by spray coating technique and its application in polymer solar cells

This study aims to investigate the effects of synthesizing undoped, doped, and co-doped ZnO nanoparticles at low temperatures (≤150 °C) and using them as electron transport materials in inverted-type organic solar cell structures via spray coating method under atmospheric conditions. In this context, three different elements (Al, Sn, and Y) were doped at mass ratios of 0.5%, 1%, 3%, and 5%, respectively. The structural characteristics of all samples were examined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The optical properties were characterized using an ultraviolet-visible UV-VIS spectrophotometer. The evaluation of photovoltaic performance involved assessing key parameters such as open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF), and power conversion efficiency (PCE). Specifically, the doping of Al resulted in a reduction in particle size and an improvement in Jsc, leading to enhanced photovoltaic performance of the cells. Undoped ZnO nanoparticle-based cells were set as the reference with a PCE of 1.59%. Among all cases considered, single-doped cells with 5% Al exhibited the best photovoltaic performance with a PCE of 3.72%. Furthermore, experiments were conducted using different co-doping ratios, including (%0.5 Al-%0.5 Sn), (%0.5 Sn-%1 Y), (%0.5 Al-%1 Y), and (%0.5 Al-%1 Sn). The results showed that co-doped ZnO nanoparticles enhanced the photovoltaic performance of solar cells. The highest PCE of 2.40% was achieved for the (%0.5 Al-%1 Sn) case. The co-doping of Sn and Y, which was tested for the first time in the known literature for the (%0.5 Al-%1 Y) case, demonstrated the potential to improve the performance of solar cells with a PCE of 1.99%. All these findings emphasize the significant factors of ZnO nanoparticles that affect the performance of inverted-type organic solar cells and provide suitable doping ratios and conditions.