Proceedings of nanoGe Fall Meeting19 (NFM19)
DOI: https://doi.org/10.29363/nanoge.nfm.2019.215
Publication date: 18th July 2019
Perovskite solar cells due to outstanding absorption and charge transport properties are one of the most promising types of photovoltaic devices. The possible ion migration, several ions content and non-mono crystal structure makes them really intriguing as well as challenging system to investigate by optical techniques. Electrons in perovskite system, after absorption, are promoted from valence to conduction band. First hundreds of femtosecond after absorption are governed by cooling of hot carriers. When the process is finished, sharp absorption bleach due to the band filling phenomena occurs which decay correlates with photoluminescence kinetics and represents the excited carrier lifetime [1]. This decay proceeds by several paths such as recombination (first-, second- and third-order) and injection to electron transporting material (ETM) or hole (HTM) transporting material.
We focused on triple cation perovskite FA0.76MA0.19Cs0.05(I0.81Br0.19)3 sandwiched between spiro-OMeTAD and mesoporous TiO2 layers prepared in open air conditions. We performed femtosecond to nanosecond transient absorption studies as well as picosecond to nanosecond time-resolved emission decays measurements of the prepared cells. Different placement of excitation within perovskite material is realized by varying the excitation side (either from TiO2 or spiro-OMeTAD side) and wavelength. We observed strikingly different dynamical and spectral responses when the excitation localized close to ETM (TiO2) or HTM (spiro-OMeTAD). In the case of ETM interface the carrier lifetime is usually shorter than for HTM interface, and both transient and stationary absorption and emission bands are shifted more to the red. This indicates the possible different properties of the perovskite material close to the contacts with ETM and HTM. We have also observed the correlation of the charge lifetime with photocurrent of the cells, similar to our recent studies on mixed methylammonium and formamidinium solar cells [2].
We also introduced additional bias illumination and bias voltage during the femtosecond transient absorption experiments to make the measurements under real operating conditions for the solar cell. Additionally, we studied an influence of DMSO concentration (DMF:DMSO ratio) in precursor solution on macroscopic and microscopic cell parameters such as photovoltaic parameters, recombination rate constant, electron lifetime, absorption and aging.
The study was supported by Polish Ministry of Science and Higher Education under project 0019/DIA/2017/46.
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