Heterostructural perovskite solar cell constructed with Li-doped p-MAPbI3/n-TiO2 PN junction

Abstract

Traditional P-i-N perovskite solar cells have achieved high efficiency over 25%, but the device structure is relatively complex, and generally requires expensive low-conductivity p-type organic semiconductors as hole transport materials. As a typical semiconductor, it is very important to realize the bipolar doping of methylamine lead iodine (CH3NH3PbI3) that is the light-absorbing layer of perovskite solar cell. Also, it is significant to develop perovskite cells with new device structure. Here, we chose lithium iodide (LiI) as the dopant and successfully grow p-type Li+ doped CH3NH3PbI3 (MAPbI3:Li) perovskite films with low resistivity (103 Ω•cm). The temperature-dependent photoluminescence, Hall effect and Kelvin probe force microscope (KPFM) results strongly confirmed that Li+ doping promotes the transformation of pristine weak n-type MAPbI3 to intentionally doped p-type film. Subsequently, the p-type MAPbI3 film is used as both the light absorption layer and hole transport layer, and form a PN heterojunction with n-type titanium dioxide (TiO2), which is used as the electron transport layer, to construct the heterostructural perovskite cell with a photoelectric conversion efficiency (PCE) of 10.43%. The electron beam induced current (EBIC) signal also strongly confirms the existence of the PN heterojunction and the new working mechanism of such new solar cells.