Organic-inorganic hybrid perovskite is a promising candidate for next generation photovoltaics with its superior performance and low cost processes. With just a few years of active research and development, great progresses have been made for perovskite solar cells (PSCs) in terms of efficiency, stability and scalability, advancing its path towards commercialization. One interesting feature of perovskite material comparing to the traditional photovoltaic materials (Si, CdTe, etc.) is the high mobility of its ionic constituents. Large current-voltage (J-V) hysteresis is believed to be one major consequence of the ionic movement in the PSCs. Movements of the ions also play roles in modulating device interfaces and accelerating degradation in PSCs. In this presentation, we will show that not only the intrinsic ions (e.g. CH3NH3+, I-), extrinsic ions such as Li+, Na+ and H+, when used in the contact layers in PSCs, can migrate across the perovskite layer and strongly impact the operation of PSCs. Using evidences from time-of-flight secondary-ion mass spectrometry, time-resolved photoluminescence, Kelvin probe force microscopy, we show that Li+ ions can migrate from spiro-OMeTAD to the TiO2 electron transport layer and improve the charge separation at the TiO2/perovskite interface. The movement of Li+ ions also introduces larger J-V hysteresis in PSCs. Similar modulation effects can be seen with other extrinsic ions such as H+ and Na+. These results demonstrate the important roles of extrinsic ion migration in PSCs, especially to the origins of hysteresis.

Extrinsic ion migration in perovskite solar cells

254th National Meeting (2017)

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