Substrate-Dependent Effects on the Growth of Methylammonium Lead Iodide Perovskites via Close Space Vapor Transport

Close space vapor transport is used to investigate PbI2 deposition and the reaction of PbI
₂
with CH
₃
NH
₃
I to form CH
₃
NH
₃
PbI
₃
(MAPI) on nanocrystalline (CdS) or amorphous (SnO
₂
) electron transport layers (ETL). The crystallographic structure and surface morphology of PbI
₂
thin films and the resultant MAPI films after reaction have strong dependence on ETL substrates. Smoother morphology, stronger crystallographic orientation - (001) for PbI
₂
and (200) for MAPI films - and larger coherency length are observed for films grown on SnO
₂
ETL as compared to CdS. Solar cells fabricated on both types of ETL exhibit better cell performance for the MAPI absorbers that contain a small amount of residual PbI
₂
. Despite crystallographic differences, solar cells made on both ETLs performed similarly.