  Due to the photo-instability and hysteresis of TiO$_2$ electron transport
layer (ETL) in perovskite solar cells (PSCs), novel electron transport
materials are highly demanded. Here, we show ideal band alignment between
La-doped BaSnO$_3$ (LBSO) and methyl ammonium (MA) lead iodide perovskite
(MAPbI$_3$). The CH$_3$NH$_3$PbI$_3$/La$_x$Ba$_{(1-x)}$SnO$_3$ interface forms
a stable all-perovskite heterostructure. The selective band alignment is
manipulated with band gap renormalization by La-doping on the Ba site. LBSO
shows high mobility, photo-stability, and structural stability, promising the
next generation ETL materials.
