For instance, measuring the efficiency of a perovskite solar cell can depend on things like how long the device is illuminated prior to measurement or how the voltage was applied. A few years ago, this effect, known as current-voltage hysteresis, led to disputes on how to accurately determine the efficiency of perovskites. Another example of these obscure processes is a (partial) recovery of a previously degraded solar cell during day-night cycling.
Such effects are a concern when measuring the solar cells' performance as a function of frequency, which is a typical measurement for characterizing these devices in more detail (impedance spectroscopy). They lead to large signals at low frequencies (Hz to mHz) and giant capacitance values for the (mF/cm2), including strange, "unphysical" negative values that are still a puzzle to the research community.
Engineers - Lab - Anders - Hagfeldt
Now, chemical engineers from the lab of Anders Hagfeldt...
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