Thermal Assisted Oxygen Annealing for High Efficiency Planar CH3NH3PbI3 Perovskite Solar Cells

We report investigations on the influences of post-deposition treatments on the performance of solution-processed methylammonium lead triiodide (CH3NH3PbI3)-based planar solar cells. The prepared films were stored in pure N-2 at room temperature or annealed in pure O-2 at room temperature, 45 degrees C, 65 degrees C and 85 degrees C for 12 hours prior to the deposition of the metal electrodes. It is found that annealing in O-2 leads to substantial increase in the power conversion efficiencies (PCEs) of the devices. Furthermore, strong dependence on the annealing temperature for the PCEs of the devices suggests that a thermally activated process may underlie the observed phenomenon. It is believed that the annealing process may facilitate the diffusion of O-2 into the spiro-MeOTAD for inducing p-doping of the hole transport material. Furthermore, the process can result in lowering the localized state density at the grain boundaries as well as the bulk of perovskite. Utilizing thermal assisted O-2 annealing, high efficiency devices with good reproducibility were attained. A PCE of 15.4% with an open circuit voltage (V-OC) 1.04 V, short circuit current density (J(SC)) 23 mA/cm(2), and fill factor 0.64 had been achieved for our champion device.