Effects of HI Additive on the Crystallization of Perovskite in Printed Mesoscopic Scaffolds

Abstract

Carbon-based fully printable perovskite solar cells (CFP-PSCs) are attracting interests of many researchers, because of their easy large-scale fabrication and their high stability. In order to improve the photovoltaic conversion efficiency (PCE) of PSCs, it is necessary to optimize the crystallization processes of perovskite films. Hydrogen iodide (HI) additive enhances the solubility of PbI2 or PbCl2 and retards the growth of perovskite crystals, resulting in round-shaped crystals and high photovoltaic efficiency. In this paper, the effects of HI additive on the PCE and stability of the CFP-PSCs are tested. It is found that PCE enhancement was achieved by mixing much smaller concentration of HI additive into the precursor solution as compared to the concentrations in other reports. The mesoscopic scaffolds might suppress the evaporation of HI additive, thereby enhancing the effects of HI additive. Adding 50 mg% HI into perovskite precursor solution, the many characteristics such as the penetrability of the precursor into the mesoscopic scaffolds, the crystallization of perovskite and charge transfer were improved, whereas charge recombination was reduced. Accordingly, the PCE of the devices with 50 mg% HI additive are improved from 10.12% (the device without HI additive) to 11.27%, corresponding 10% higher efficiency. The morphologies of perovskite crystals could be different between the inside and the surface of the mesoscopic scaffold due to the difference of the evaporation rates of HI additive. This result suggests that the removal dynamics of additive changes the effects of additive on the perovskite crystallization.