Investigating the effect of inorganic cation additives on the properties of double cation perovskite system
Hadi, Harri Dharma
Date of Issue2017
School of Materials Science and Engineering
Fabrication of perovskite absorber layer with high purity is an important prerequisite to produce solar cell with good performance. The earliest organic-inorganic perovskite absorber layer composed of MAPbX3 (MA+= Methylammonium (cation) , X- = halogen (anion) ). However, this type of perovskite layer suffered from poor phase stability. Hence, researchers had started to use compositional engineering by adding another Formamidinium cation (FA+) to produce MA/FA double cation system. This system had an increased perovskite phase stability, but impurity phase still appeared frequently. Recently, addition of Cs+ to MA/FA system was shown to suppress the impurity effectively and the perovskite film had an improved crystallinity and reproducibility. This has motivated me to further investigate the effect of adding different kinds of inorganic cation additives such as Cs+, Rb+, K+ or NH4+ with several content variation to the double cation (MA/FA) system. Both iodide and bromide salt are chosen as those additives sources. In this experiment, the perovskite layers were deposited by using one-step spin coating method in high purity argon controlled glovebox. In this study, phase investigation was analyzed using X-Ray Diffraction .It was found that substitution of sufficient amount of Cs+ and Rb+ to the double cation system could result in a perovskite film with no trace of residual PbI2 and yellow phase FAPbI3. In terms of XRD patterns, there was no significant difference in using iodide or bromide salt sources. Furthermore, bandgap analysis obtained from UV-Vis Spectroscopy indicated that different kind and content of the inorganic cation additives would result in different amount of bandgap shift. The inorganic cation additives salt sources also strongly affected the bandgap. Meanwhile, the charge carrier lifetime, which was measured using Time-Resolved Photoluminescence (TRPL) showed that addition of relatively small amount of inorganic cation to the double cation system could significantly improve the lifetime of the perovskite film. Notably, additives from iodide salt sources had longer lifetime than bromide salt sources. The findings from this study were expected to give guidance for selection of suitable inorganic cation additives and their sources to maximize the performance of triple cation perovskites for photovoltaic applications.
Final Year Project (FYP)
Nanyang Technological University