(604b) Engineering Perovskite Solar Cell Interfaces to Realize > 1000 Hr, Unencapsulated Ambient Stability
In this study, we systematically investigate the interfaces in the typical n-i-p perovskite solar cell, identify key degradation mechanisms, and systematically engineer these interfaces to improve operational stability. Replacing spiro-OMeTAD with a Li+-free hole transport layer (HTL) material, EH44,5 we can achieve power conversion efficiencies of approximately 18% in a standard TiO2/perovskite/HTL/Au device stack. Unencapsulated devices utilizing EH44 show a factor of 4 better ambient operational stability compared to spiro-OMeTAD devices, after a similar initial burn-in of the devices. Analyzing the initial burn-in, Time of Flight Secondary Ion Mass Spectrosocpy (ToF-SIMS) on the device stack shows a redistribution of the perovskite active layer during the initial burn-in which is independent of the HTL. This redistribution, and the corresponding burn-in, is driven by interface effects and is significantly reduced when the TiO2 electron transport layer (ETL) is replaced with SnO2. When combined with MoOx/Al electrodes,6 this device stack allows for a ~3 order of magnitude increase in the operational stability of unencapsulated devices in ambient conditions. We observe only a 12% decrease in efficiency after 1000 hrs of continual ambient operation (6% degradation in best device). The ability of these devices to withstand the combined stresses of UV-light, oxygen, and moisture, demonstrates the importance of carefully designed interfaces for realizing true long-term stability.
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