Charge injection dynamics from organometal halide perovskite into organic electrodes

Tom Savenije^a, Villy Sundström^b, Tonu Pullerits^b, Arkady Yartsev^b, Kaibo Zheng^b, Carlito Ponseca ^b, Mohamed Abdellah^b

^aDelft University of Technology, The Netherlands, Julianalaan, 136, Delft, Netherlands

^bLund University, Department of Chemical Physics, Getingevägen 60, Lund, 22241, Sweden

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Oral, Tom Savenije, presentation 282
Publication date: 5th February 2015

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 up to 20%. Surprisingly, the exact mechanism how charges are generated and extracted so well is unclear. In this paper, we report on the dynamics of electron injection from CH₃NH₃PbI₃ into PCBM and of hole injection into Spiro-OMeTAD, using terahertz spectroscopy and time-resolved microwave conductivity measurements. For intrinsic CH₃NH₃PbI₃ depositedon 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 mm. In a CH₃NH₃PbI₃/PCBM bilayer electron diffusion and injection into PCBM occurs on a slow, nanosecond timescale. After interfacial electron injection the charge carriers exhibit longer lifetimes than in the neat perovskite. In contrast in a CH₃NH₃PbI₃/Spiro-OMeTAD bilayer, hole injection into Spiro-OMeTAD is occurring on a sub-nanosecond timescale. However, rapid interfacial recombination leads to charge carrier lifetimes in the order of approximately 100 ns. We propose that 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. Furthermore we expect that the large difference in dynamics for both junctions is related to the type of junction formed at both interfaces. Our results highlight the need to optimize the conductivity of electrode materials in order to enhance the charge extractionto push the overall power conversion efficiency further.

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