The Role of Oxygen Exposure on the Performance of All-Vapor-Processed Perovskite Solar Cells with CuPC Hole Transport Layers

Methylammonium lead iodide perovskite solar cells were made using an all-vapor process, including two-step close space vapor transport-processed MAPI and evaporated copper phthalocyanine (CuPC). Solar cells fabricated entirely in a nitrogen glovebox had poor performance due to s-shaped J-V curves and fill factors (FF) <45%. Solar cells exposed to dry air in a desiccator for 7 days, or where O
2
was flowed into the evaporator during CuPC deposition, had significantly improved performance with reduced or eliminated s-shaped behavior and improved FF up to 71%. Parallel contact conductivity measurements show that exposure to dry air, deposition with oxygen, and MoO
x
capping layers all increase the conductivity of the CuPC. SCAPS simulations show that increasing hole concentration consistent with oxygen doping effects can explain the J-V behavior of the solar cells.