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C2.02 - Charge Injection Dynamics from Organometal Halide Perovskite into Electrodes Evidence of Slow Hole Extraction 
April 7, 2015   1:45pm - 2:00pm

Organometal halide perovskites have recently attracted enormous attention since CH3NH3PbX3 can be successfully applied as photoactive material in photovoltaic devices, yielding solar cells with an efficiency exceeding 15%. Surprisingly, the exact mechanism how charges are generated and extracted so well is unclear. In this paper, we report the dynamics of electron injection from CH3NH3PbI3 into PCBM and hole injection into Spiro-OMeTAD, using time resolved microwave conductivity measurements. For intrinsic CH3NH3PbI3 deposited on an inert substrate we observed fast formation of microsecond lived charge carriers. At low laser fluences a maximum charge carrier mobility of about 5 cm2/Vs, yielding charge carrier diffusion lengths well above 5 ?m is found. In a CH3NH3PbI3/PCBM bilayer electron injection into PCBM occurs on a sub-ns timescale, similar as has been found for TiO2. In contrast in a CH3NH3PbI3/Spiro-OMeTAD bilayer, hole injection into Spiro-OMeTAD is much slower, extending up to a few hundreds of ns. This large difference in dynamics is related to the type of junction formed at both interfaces. Furthermore, the low conductivity of Spiro-OMeTAD causes the hole to be essentially immobile at the interface enabling fast recombination with electrons residing in the perovskite. These results highlight the need to optimize the conductivity of hole transporting materials in order to enhance the hole extraction to push the overall power conversion efficiency further.

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