Methylammonium lead iodide grain boundaries exhibit depth-dependent electrical properties
Gordon A. MacDonald, Mengjin Yang, Samuel Berweger, Jason P. Killgore, Pavel Kabos, Joeseph Berry, Kai Zhu, Frank W. DelRio
In this letter, the nanoscale through-film and lateral photoresponse and conductivity of large-grained methylammonium lead iodide thin films are studied. In perovskite solar cells (PSC), these films result in efficiencies > 17%. The top surface of the grain boundaries (GBs) shows high resistance and acts as an impediment to photocurrent collection, while lower resistance pathways exist below the surface. These results indicate that increased photocurrent collection along GBs is not a prerequisite for high-efficiency PSCs, but that better control of depth dependence of GB electrical properties need to be managed to enable further improvements in the efficiency of PSCs.