Passivation of triple cation perovskites using guanidinium iodide in inverted solar cells for improved open-circuit voltage and stability

Inverted device architectures in perovskite research were promising for faster commercialization given the simple processing routes and choice of hole transport materials such as PEDOT:PSS. However, the crystallization of perovskite on the PEDOT:PSS surface led to large domains with several grain boundaries and defects, especially when multi cation systems are involved. Defects formed on the surface of the perovskite are significant reasons for non-radiative recombination, which then limits the performance of the device. Surface passivation of the perovskites through the introduction of large cations was shown as a viable option to minimize the defects and promote better charge carrier extraction. In this regard, recent research was mostly limited to planar architectures and on perovskites prepared on mesoporous TiO2 films. In this work, we report the deposition of guanidinium iodide (GUAI) on the triple cation FAMAC perovskite prepared on a PEDOT:PSS surface in an inverted architecture as a means to induce passivation and suppress non-radiative recombination. We examine the effects of adding different concentrations of GUAI dissolved in isopropyl alcohol as a post-treatment process on triple cation perovskites. The passivation effect led to an increase in open-circuit voltages from 0.89 V to over 0.96 V, which resulted in high efficiency of 16.03% for a GUAI loaded device compared to 12.92% for the control device. The stability was also found to be improved for GUAI passivated devices compared to a control device when tested over 600 hours of storage in ambient conditions.