Influence of spiro-ometad film thickness on the structural and electrical properties of perovskite solar cells

Abstract

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 speeds from 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.