Surface engineering of zinc oxide thin as an electron transport layer for perovskite solar cells

This work investigates the zinc oxide (ZnO) deposited by the spin coating technique which has for the main advantage of its implementation. Zinc oxide is a semiconductor that has a direct optical bandgap of 3.3 eV which has transparency properties of about 80% optical, anti-reflection in the UV-Vis spectrum, and high electrical conductivity (Cao et al. 2018). The electron transport layer (ETL) is one of its main functions in a solar cell. The number of spin coatings was changed from 1 to 4 in order to get different variations of ZnO thicknesses. These different samples were characterized. X-Ray Diffraction (XRD) showed the polycrystalline character of the ZnO films. Two peaks (the strongest) have been identified on planes (002) and (101). SEM showed that the surface of the samples presents a good crystallinity, which agrees with the results of XRD. Moreover, the crystallinity and the density increase with the number of cycles. The transmittance of samples obtained by spectrophotometry was about 80% in the visible and decreases with the number of cycles. Bandgap was calculated from absorbance data and it varies from 3.25 to 3.29 eV. The best sample was the sample with four cycles (ZnO-4). It was used for heterojunction with mixed halide methylammonium lead (MAPbBr 2 I). The bandgap obtained of the heterojunction MAPbBr 2 I/ZnO-4 was 1.9 eV. The simulation of the mixed halide methylammonium lead (MAPbBr 2 I) base-solar cell resulted in 16.938095 mA/cm 2 , 2 V, and 33.88% for Jsc, Voc, and eta respectively.