The role of organic cations as additives in photovoltaic perovskites.

The design of additives for perovskite-based solar cells seeks to improve the balance between stability and power conversion efficiency. Organic molecules such as theophylline, theobromine and caffeine (xanthines) have proved to be a good engineering solution. As an alternative, we present a first-principles study of the use of organic cations as additives. These cations are obtained when the free nitrogen of the imidazole unit of the aforementioned molecules is quaternized. We have found that the interaction between the organic cations and the MAPbI3 perovskite surface is stronger compared to the organic molecules. The Pb-O and I-H bonds of the interface dominated these interactions. In addition, organic cations showed higher charge transfer through the interface and shallow states that are harmless and could improve the charge carrier mobility. These characteristics show that quaternized xanthines should be a promising additive for perovskite materials in photovoltaic applications.

Enhancing the stability and efficiency of MAPbI3 perovskite solar cells by theophylline-BF4 - alkaloid derivatives, a theoretical-experimental approach.

Perovskite solar cells (PSCs) are an evolving photovoltaic field with the potential to disrupt the established silicon solar cell market. However, the presence of many transport barriers and defect trap states at the interfaces and grain boundaries has negative effects on PSCs; it decreases their efficiency and stability. The purpose of this work was to investigate the effects on efficiency and stability achieved by quaternary theophylline additives in MAPbI3 PSCs with the structure FTO/TiO2/perovskite/spiro-OMeTAD/Ag. The X-ray photoelectron spectroscopy (XPS) and theoretical calculation strategies were applied to study the additive's interaction in the layer. The tetrafluoroborinated additive results in an increase in device current density (J SC) (23.99 mA cm-1), fill factor (FF) (65.7%), and open-circuit voltage (V OC) (0.95 V), leading to significant improvement of the power conversion efficiency (PCE) to 15.04% compared to control devices (13.6%). Notably, films exposed to controlled humidity of 30% using the tetrafluoroborinated additive maintained their stability for more than 600 hours (h), while the control films were stable for less than 240 hours (h).