Improved morphological characteristics and electronic properties of MAPbI₃ thin film with multiple methylamine spray treatments

We demonstrated that the quality of the film can be significantly improved by using multiple treatments with methylamine (CH₃NH₂, MA) spray to the spin-coated perovskite thin films on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/ITO glass substrates, leading to more efficient and reproducible photovoltaic and optoelectronic devices. Our X-ray diffraction and scanning electron microscopy measurements indicated an increase in the homogeneity, grain size, and crystallinity of the spin-coated MAPbI₃ thin film after multiple MA vapor treatments. The influence of MA vapor treatments on emission, absorption, energy gap, and carrier lifetime were investigated through the absorption, steady-state, and time-resolved photoluminescence (PL) spectroscopy. The peak position and full width at half maximum of the MA spray-treated film PL were slightly blue shifted and narrowed, respectively, because of the reduced defect states in the band tail and gain boundary. However, the PL intensity of the treated film was lower than that of the untreated one due to the increased carrier diffusivity in larger grains. The carrier type, concentration, mobility, electrical resistivity, and photoconductivity of the MA spray-treated MAPbI₃ thin film was also investigated using the Hall and current-voltage measurements. The improvements in the morphological characteristics and crystallinity of the treated perovskite thin film were reflected in the enhanced carrier mobility, electrical conductivity, photo response, and suppressed carrier recombination.