INFLUENCE OF SPIRO-OMETAD FILM THICKNESS ON THE STRUCTURAL AND ELECTRICAL PROPERTIES OF PEROVSKITE SOLAR CELLS

This work investigates the effect of the hole transport layer (HTL) thickness of Spiro-OMeTAD on the electrical transport properties in perovskite solar cells (PSCs).Spiro-OMeTAD films were obtained by the spin-coating method at centrifuge rotation speedsfrom 2000 to 7000 rpm. The thickness and morphology of the Spiro-OMeTAD films were studied by atomic force microscopy (AFM). From the obtained AFM image data, an increase in the surface root mean square (rms) value is observed with decreasing film thickness. A decrease in film thickness leads to an increase in Energy gap (Eg)from 2.97 eV to 3.01 eV. We observe that at a layer thickness of 260 nm, the efficiency of the cells reaches its maximum value; further increasing the layer thickness reduces the efficiency. Analysis of the impedance spectra of PSCs showed that the optimal layer thickness reduces the HTL resistance and increases the recombination resistance at the perovskite/HTL interface, which increases the effective lifetime of charge carriers. Images of the surface and current distribution of Spiro-OMeTAD on the surface of the perovskite layer were studied.A non-uniform current distribution on the surface of the samples was revealed, the observed spots with high conductivity are interpreted as perovskite quantum dots, which have better photovoltaic characteristics.Keywords: Perovskite solar cells, hole transport layer,Spiro-OMeTAD, conductive-AFM, current-voltage characteristics, impedance measurements.1. Introduction In recent years, organic-inorganic perovskite solar cells have attracted much attention from the global scientific community. The unprecedented development of PSCs is driven by their high optical absorption coefficient, tunable bandgap, low cost, ease of fabrication, and great potential to achieve higher efficiency compared to c-Si solar cells [1–3].To increase the efficiency and stability of PSCs, work is being done to search and optimize the composition of all parts of the solar cell, not only the perovskite itself, but also theso-called transport layers. The hole-conducting transport layer plays an important role in the efficiency of charge transfer and extraction of photoexcited perovskite, HTL is important for power conversion efficiency (PCE) and stability in PSCs. Transportlayers typically consist of small organic molecules, polymers, or inorganic materials such as oxides. The energy level of the HTL material must coincide with the maximum