Performance and stability of co-evaporated vapor deposited perovskite solar cells

In this work, we report on the influence of fabrication conditions and on the performance and stability of co-evaporated vapor deposited methyl ammonium lead iodide (MAPbI₃) perovskite solar cells. It is shown that as the substrate temperature increases, one has to increase the flux of MAI as indicated by higher vapour pressure in the reactor to maintain the appropriate stoichiometry of the devices. The pressure of MAI was maintained at 5.5–6 × 10⁻⁵ Torr and PbI₂ rate of deposition was maintained at 0.75 A/s for a room temperature substrate deposition. For higher substrate temperature depositions at 50 °C and 75 °C we had to elevate the MAI pressure because of re-evaporation of MAI from the substrate at higher temperatures. A power conversion efficiency of > 17.4% has been achieved with a p-i-n device architecture of FTO/PTAA (polytriaryl amine)/MAPbI₃/PCBM (phenyl-C61-butyric acid methyl ester)/Al through careful control of the MAI pressure and PbI₂ evaporation rate. Higher substrate temperature devices showed improved grain sizes. The devices do not show any hysteresis. Devices deposited at higher substrate temperatures are significantly more photo stable over 100 h of continuous light exposure in nitrogen ambient.