Recombination and Hysteresis in Perovskite Solar Cells
Michael Graetzel a, Antonio Abate a, Michael Saliba a, Konrad Domanski a, Wolfgang Tress a, Juan Pablo Correa-Baena b, Anders Hagfeldt b
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics (AP-HOPV17)
Yokohama-shi, Japan, 2017 February 2nd - 4th
Organizers: Tsutomu Miyasaka and Iván Mora-Seró
Oral, Wolfgang Tress, presentation 067
Publication date: 7th November 2016

On the one hand, perovskite solar cells show large open-circuit voltage indicative of suppressed recombination, which is a beneficial phenomenon for a solar cell. On the other hand, the current-voltage relation exhibits hysteretic behavior, implying a strong dependence of photocurrent extraction on the (previously) applied voltage and therefore the electric field. This is detrimental as it comes along with reduced fill factor and, though (mainly) reversible, losses in efficiency and possibly long term stability. The slow processes are attributed to ion migration in the perovskite.

In this contribution we shed light onto the interrelation between the two phenomena of high voltage and ion migration. Using mixed perovskite compositions with power-conversion efficiencies of around 20 %, we show that the high voltages are only possible in case of efficiently suppressed surface recombination. We investigate the role of the charge transport layers and energetic barriers and find that the charge transport properties of these layers indirectly influence hysteresis, in extreme case resulting in a new type of inverted hysteresis.

These findings accompanied by device modeling provide explanations on the effect of the electric field, charge recombination, and ionic motion aiming towards a more complete picture of the working principle of perovskite solar cells.

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