Atmospheric effects on the photovoltaic performance of hybrid perovskite solar cells

​Arif D Sheikh a , Ashok Bera a , Md Azimul Haque a , Raghavan B. Rakhi a , Silvano Del Gobbo b , Husam N. Alshareef a , Tom Wu, "Atmospheric effects on the photovoltaic performance of hybrid perovskite solar cells"
​Solar Energy Materials and Solar Cells Volume 137, June 2015, Pages 6–14
Arif D Sheikh a, Ashok Bera a, Md Azimul Haque a, Raghavan B. Rakhi a, Silvano Del Gobbo b, Husam N. Alshareef a, Tom Wu
Solar cell; Perovskite; Organometal halide; spiro-MeOTAD
​Organometal trihalide perovskite solar cells have recently attracted lots of attention in the photovoltaic community due to their escalating efficiency and solution processability. The most efficient organometallic mixed-halide sensitized solar cells often employ 2,20 7,70 -tetrakis-(N,N-di-p-methoxyphenylamine)-9,90 -spirobifluorene (spiro-MeOTAD) as the hole-transporting material. In this work, we investigated the effect of different atmospheric storage conditions, particularly vacuum, dry nitrogen, and dry air, on the photovoltaic performance of TiO2–CH3NH3PbI3xClx–spiro-MeOTAD solar cells. We found that spin coating of spiro-MeOTAD in an oxygen atmosphere alone was not adequate to functionalize its hole-transport property completely, and our systematic experiments revealed that the device efficiency depends on the ambient atmospheric conditions during the drying process of spiroMeOTAD. Complementary incident photon to current conversion efficiency (IPCE), light absorption and photoluminescence quenching measurements allowed us to attribute the atmosphere-dependent efficiency to the improved electronic characteristics of the solar cells. Furthermore, our Fourier transform infrared and electrical impedance measurements unambiguously detected modifications in the spiroMeOTAD after the drying processes in different gas environments. Our findings demonstrate that proper oxidization and p-doping in functionalizing spiro-MeOTAD play a very critical role in determining device performance. These findings will facilitate the search for alternative hole-transporting materials in highperformance perovskite solar cells with long-term stability.