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The fill factor ( FF ) of perovskite solar cells is considerably lower than that of gallium arsenide and silicon cells, though they have similar open‐circuit voltage deficits. To probe the FF loss, which mainly comes from series resistance, the J sc – V oc characterization technique is applied to perovskite solar cells. A continuous‐lamp solar simulator with an array of neutral density filters is used instead of the quasi‐steady‐state photoconductance technique commonly employed for silicon cells, which allows us to tune sweep parameters to accommodate the complex behavior of perovskites such as hysteresis. It is found that, for Cs 0.25 FA 0.75 Pb(Br 0.2 I 0.8 ) 3 (CsFA) perovskite cells, sweeping from positive to negative voltage yields the same series resistance regardless of sweep speed, whereas this is not the case if the sweep is reversed. However, for CH 3 NH 3 PbI 3 perovskite cells, the series resistance is independent of the sweep speed in both sweep directions. It is also found that, for a polybis(4‐phenyl)(2,4,6‐trimethylphenyl)amine (PTAA) hole contact, increasing the PTAA thickness barely changes the recombination‐limited pseudo‐ FF , but reduces the FF due to increased series resistance. A maximum FF of 80.9% was achieved with the PTAA hole contact on a CsFA perovskite absorber.
Mundhaas et al. (Wed,) studied this question.