Low cost copper phthalocyanine has been used as hole-transporting material for the construction of organolead halide solid state perovskite solar cells.
Small
perturbation techniques have proven to be useful tools for
the investigation of perovskite solar cells. A correct interpretation
of the spectra given by impedance spectroscopy (IS), intensity-modulated
photocurrent spectroscopy (IMPS), and intensity-modulated photovoltage
spectroscopy (IMVS) is key for the understanding of device operation.
The utilization of a correct equivalent circuit to extract real parameters
is essential to make this good interpretation. In this work, we present
an equivalent circuit, which is able to reproduce the general and
the exotic behaviors found in impedance spectra. From the measurements,
we demonstrate that the midfrequency features that may appear to depend
on the active layer thickness, and we also prove the spectral correlation
of the three techniques that has been suggested theoretically.
An inorganic solar cell was constructed using a thin compact supporting layer of titania with BiOI nanoflakes as a functional material, a Pt/FTO cathode and a I3−/I− redox electrolyte.
A range of slow dynamic processes occurring in perovskite solar cells have been linked to ionic migration, including J−V hysteresis and long photovoltage rise and decay times. This work demonstrates the remarkably slow response time of triple mesoporous carbon-based cells, containing the additive 5aminovaleric acid iodide (AVA). The photovoltage rise under illumination is 1−2 orders of magnitude longer than has previously been observed for planar and mesoporous TiO 2 based devices. Transient photovoltage measurements during this slow rise in voltage show a strong negative transient feature which demonstrates the presence of fast recombination. By analyzing the rate of V oc rise and the decay of this negative transient, we show a clear link between this recombination process and the limiting of the V oc . The reduction of recombination over time and the resultant rise in V oc are influenced by the movement of ions in the perovskite. From temperature-dependent measurements, an activation energy consistent with previous literature values for iodide ion migration is obtained, although the attempt frequency is found to be many orders of magnitude lower than that in pure MAPI perovskite devices. We attribute this to the presence of the AVA molecule inhibiting the movement of ions. The importance of the TiO 2 /ZrO 2 interface in leading to this slow behavior is revealed by studying devices with different architectures with and without the AVA additive. A significant increase in response time can only be recreated in a device with both of the mesoporous metal oxide layers and the AVA additive present in the perovskite.
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