Stability Improvement of Low-bandgap Perovskite Solar Cell Using Formamidinium as Cation

Abstract

In this thesis in order to improve the stability of the perovskite solar cells we substituted original cation of typical perovskite solar cells Methylammonium (MA) with Formamidinium (FA) Because of the higher crystallization temperature of FA perovskite solar cells we assumed that the binding energy of FA perovskite solar cells was higher than MA perovskite solar cells enhancing the resistance of oxide and moisture and finally enlarging its stability Moreover using formamidinium as the cation can reduce the bandgap of the perovskite solar cells which means its absorption edge shifts to longer wavelength We can apply this type of solar cells on tandem-structure perovskite solar cells since it can absorb near-IR wavelength light of sunlight In addition so as to enhance its stability further we used lead thiocyanate (Pb(SCN)2) as additive which can enlarge grain size and crystallinity of perovskite phase For FA-based perovskite solar cell has a tolerance factor larger than 1 it’s difficult to form high quality black phase FAPbI3 and easy to become yellow phase an unfavorable phase for perovskite solar cells Therefore adding small amount of methylammonium and lead thiocyanate can restrain perovskite from forming yellow phase and it can be confirmed by X-ray diffraction measurement Meanwhile since tin and lead have similar atomic arrangement we applied tin as replacement to reduce the content of lead in perovskite solar cells with a view to being less toxicity We partially substituted lead with tin content of 12 5% 25% 37 5% in this work and we observed the more tin we substituted the lower bandgap it became Moreover 37 5% tin substitution provides the best alternative because of the highest efficiency and tin percentage In the end of this thesis we successfully improved the stability of perovskite material by using formamidinium as cation and adding lead thiocyanate in perovskite layer Formamidinium and partially tin substitution based perovskite solar cells lead to a red shift of optical absorbance compared to methylammonium and pure lead based solar cells and we hope we can apply this type of perovskite solar cells on tandem-structure solar cells

Date of Award	2018 Aug 1
Original language	English
Supervisor	Wei-Chou Hsu (Supervisor)