The Effects of Zn Doped TiO2 on the Performance of Perovskite Solar Cells

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Abstract

The work focuses on the effects of Zn-doped TiO₂ as the Electron Transport Layer in MAPbI3 based Perovskite Solar Cells with a carbon-based back electrode fabricated under controlled ambient conditions. Varying molar percentages of Zn-doped TiO₂ of 0, 0.5, 1, 2, and 5 mol% were successfully incorporated into the TiO₂ crystal structure using the sol-gel technique. Characterization through X-ray diffraction and Energy Dispersive X-ray spectroscopy confirmed the incorporation of Zn ions. The crystallite size ranged from 19.99 to 7.1 nm, depending on the Zn ion doping concentration. Fourier Transform Infrared spectroscopy verified the presence of the anatase phase of Zn-doped TiO₂ at wavenumber 438 cm^-1. Scanning Electron Microscope images exhibited fairly smooth and uniform surface coverage for the Zn-doped TiO₂ layers. The Rq values for surface roughness showed a decrease from 26.85 nm for undoped TiO₂ to 23.4 nm for the 5 mol% Zn-doped TiO₂ layer. UV-Vis spectroscopy demonstrated low light transmission loss characteristics from 300 to 790 nm, with the 2 mol% Zn-doped TiO₂ showing slightly improved light transmission between 550 and 800 nm. The bandgap energy of undoped and Zn-doped TiO₂ ranged from 3.53 to 3.38 eV. An optimum power conversion efficiency of 5.67% was achieved with a 2 mol% dopant concentration. However, increasing the Zn dopant to 5 mol% led to a slight deterioration in the PCE. According to the optimized ETL processing for the PSC, the Jsc increased from 12.2185 mA/cm² to 12.25594 mA/cm², the Voc increased slightly from 0.90569 V to 0.9231 V, and the PCE from 5.199% to 5.67%.