Jamie M. Foster

Can slow-moving ions explain hysteresis in the current–voltage curves of perovskite solar cells?

The hypothesis that ion motion is responsible for anomalous hysteresis in the current–voltage curves of perovskite solar cells is investigated through a combination of electrical transport modelling and experimental measurements. In a combined computational and experimental study, good agreement is obtained between experiment and the results of a charge transport model covering mixed ionic-electronic conduction. Our model couples electrons, holes and defect mediated ion motion suggesting that slow moving ions are indeed the origin of the hysteresis. The magnitude of the ion diffusion coefficient required to match experiment and theory, ∼10−12 cm2 s−1, depends on the cell, but is similar to that predicted by microscopic theory of vacancy mediated diffusion. The investigation is extended to preconditioning procedures which are known to substantially influence the hysteresis. The method developed for solving the stiff equations in the drift diffusion model is widely applicable to other double layer problems occurring in electrochemical applications such as the evolution of transmembrane potentials in living cells.

Migration of cations induces reversible performance losses over day/night cycling in perovskite solar cells

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.

A model for the operation of perovskite based hybrid solar cells: formulation, analysis, and comparison to experiment

This work is concerned with the modeling of perovskite based hybrid solar cells formed by sandwiching a slab of organic lead halide perovskite (CH

Asymptotic and numerical prediction of current-voltage curves for an organic bilayer solar cell under varying illumination and comparison to the Shockley equivalent circuit

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Measurement and modelling of dark current decay transients in perovskite solar cells

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Asymptotic solution of a model for bilayer organic diodes and solar cells

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Modelling in vivo action potential propagation along a giant axon

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Systematic derivation of a surface polarisation model for planar perovskite solar cells

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Self-Similar Solutions for Reversing Interfaces in the Slow Diffusion Equation with Strong Absorption

Cl

The reversing of interfaces in slow diffusion processes with strong absorption

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