Perovskites have been demonstrated in solar cells with a power conversion efficiency of well above 20%, which makes them one of the strongest contenders for next generation photovoltaics. While there are no concerns about their efficiency, very little is known about their stability under illumination and load. Ionic defects and their migration in the perovskite crystal lattice are some of the most alarming sources of degradation, which can potentially prevent the commercialization of perovskite solar cells (PSCs). In this work, we provide direct evidence of electric field-induced ionic defect migration and we isolate their effect on the long-term performance of state-of-the-art devices. Supported by modelling, we demonstrate that ionic defects, migrating on timescales significantly longer (above 10³ s) than what has so far been explored (from 10⁻¹ to 10² s), abate the initial efficiency by 10–15% after several hours of operation at the maximum power point. Though these losses are not negligible, we prove that the initial efficiency is fully recovered when leaving the device in the dark for a comparable amount of time. We verified this behaviour over several cycles resembling day/night phases, thus probing the stability of PSCs under native working conditions. This unusual behaviour reveals that research and industrial standards currently in use to assess the performance and the stability of solar cells need to be adjusted for PSCs. Our work paves the way for much needed new testing protocols and figures of merit specifically designed for PSCs.

This review provides a comprehensive overview of TiO ₂ doping, which is often used to improve the performance of dye sensitized solar cells.

With close to 100% internal quantum efficiency over the absorption spectrum, photocurrents in perovskite solar cells (PSCs) are at their practical limits. It is therefore imperative to improve open-circuit voltages (V_OC) in order to go beyond the current 100 mV loss-in-potential. Identifying and suppressing recombination bottlenecks in the device stack will ultimately drive the voltages up. In this work, we investigate in depth the recombination at the different interfaces in a PSC, including the charge selective contacts and the effect of grain boundaries. We find that the density of grain boundaries and the use of tunneling layers in a highly efficient PSC do not modify the recombination dynamics at 1 sun illumination. Instead, the recombination is strongly dominated by the dopants in the hole transporting material (HTM), spiro-OMeTAD and PTAA. The reduction of doping concentrations for spiro-OMeTAD yielded V_OC's as high as 1.23 V in contrast to PTAA, which systematically showed slightly lower voltages. This work shows that a further suppression of non-radiative recombination is possible for an all-low-temperature PSC, to yield a very low loss-in-potential similar to GaAs, and thus paving the way towards higher than 22% efficiencies.