Enhanced thermal and moisture stability via dual additives approach in methylammonium lead iodide based planar perovskite solar cells

摘要

Among various perovskite materials available methyl ammonium lead iodide (CH3NH3PbI3 or MAPI) has been the most common and extensively explored perovskite material owing to its simple synthesis technique and ease of device fabrication in regular and inverted structure. However, thermal and moisture stability constraints have led researchers to explore mixed cation/halide perovskites. In this manuscript, we report excellent thermal and moisture stability of MAPI solar cells by incorporating organic: phenyl-C70-butyric acid methyl ester (PC70BM) and inorganic: NH4Cl additives in the photo-absorber layer. Our investigations reveal that the use of NH4Cl results in large grain size hence reducing the grain interface or boundary area whilst PC70BM passivates the charge traps and bonds with the defect-inducing halogen atoms at the grain boundaries. The combined effect of the two additives results in significant improvement in the life time of unencapsulated planar device with 80% retention in the efficiency after 500 hrs of accelerated stability testing at 85 degrees C in 15-20% RH, and 85% efficiency retention after 100 days of moisture exposure in the ambient conditions (50-60% RH and 20-25 degrees C). This is believed to be due to suppression of migration of ions which is also manifested in reduced hysteresis in the devices. The champion device with the two additives showed 90% increase in power conversion efficiency (PCE) of similar to 17% as compared to pristine planar device (9.0%), attributed to bigger grain size and passivation of charge traps at grain boundaries. Detailed microscopy analysis revealed the unambiguous presence of Cl ions in the perovskite layer on addition of NH4Cl. Thus, using single-step coating method, we have achieved excellent stability for slightly chlorine doped and PC70BM passivated CH3NH3PbI3 based perovskite solar cell with reduced hysteresis.