Understanding physical mechanisms governing the response of Perovskite solarcells during efficiency measurement

Abstract

This study investigates the influence of different physical mechanisms on the electrical behaviour of Perovskite photovoltaic cells. An investigation of the problem of ambiguous results during electrical property measurement and the lack of the comparability of these results is conducted. It aims at contributing to the establishment of a guideline for these measurements by proposing a procedure to improve I-V curve measurement. Three different CH3NH3PbI3 inverted structure cells were mainly studied, one fabricated by the author, the other two fabricated by a research group from the University of Oxford. The influence of irradiance level, temperature, voltage steps of different sizes, influence of time as well as light soaking treatment is studied. A procedure of estimating appropriate dwell times for the I-V curve measurement is proposed and tested on a silicon, dye and Perovskite cell. According to that procedure the cell’s electrical parameters are measured in a steady state, thus improving the comparability of different cells as they are all measured the same state. A memory effect (lasting more than six hours) is identified as a reason for the poor reproducibility of transient current behaviour and intensely investigated. The cell’s electrical behaviour does change depending on the history of exhibition to light and testing conditions but does return to an initial state after a sufficient resting time in the dark. That effect is found to be existing for the Oxford as well as the author’s cell yet expressed in different ways. Whereas the author’s cell’s transient current behaviour is impaired by that memory effect, the effect is expressed in the Oxford cell as a memory of light soaking history. An improvement of the cells open circuit voltage and maximum power due to a light soak is observed. Once light soaked once that is state re-achieved quickly even after longer periods in the dark of more than 12 hours. Giving the cells a sufficient resting time in the dark (two days), the memory effect is fully cleared. The attempt is made to clear the cell’s memory in few minutes to shorten measurement procedures in general. A partial recovery of the cell’s initial state is reproducibly achieved. Further approaches for future research are proposed including the proposals for the memory clearance well and a way of utilizing the dwell time estimation method.