Effects of halogens and alkali metals on guanidinium/ethylammonium-doped perovskite photovoltaic devices

Perovskite solar cells are expected to be alternative materials to silicon solar cells because of their high conversion efficiencies and easy device fabrication with various compositions. Recently, research is being conducted to develop low-cost and flexible devices. For the typical CH₃NH₃PbI₃ perovskite, CH₃NH₃ (MA) migration and high reactivity have a significant impact on instability and low durability in the atmosphere. To solve this problem, research has been conducted to improve crystal stability by introducing elements and molecules into perovskite crystals. Among organic molecules, guanidinium (GA), which has three different resonance structures and is stable, and ethylammonium (EA), which has a larger ionic radius than MA, will contribute to crystal stabilization by introduction into the crystal lattice. Additionally, alkali metal cations are expected to be difficult to desorb due to their inorganic nature. In this study, effects of substitution of halogen anions and addition of alkali metal cations for GA/EA-doped perovskite solar cells were investigated by fabricating devices and comparing their photovoltaic properties. The halogen compositions of the additives were found to contribute to the improvement of preferred orientations of perovskite crystals, and the order of the effectiveness was I, Cl, and Br. In addition, the addition of alkali metal cations contributed to improvement of the conversion efficiencies, and addition of a small amount of cesium at the MA site was the most effective. It was also found that the short-circuit current densities and fill factors depended on the (100) preferred crystal orientation of the perovskite compounds.