Ion mobility independent large signal switching of perovskite devices

Abstract

The presence of mobile ions in perovskites is well known to influence the device electrostatics leading to a wide variety of anomalous characteristics related to hysteresis, efficiency degradation, low frequency capacitance, large signal switching, etc. Accordingly, the ion mobility is understood to a have a critical influence on the associated time constants/delays. Quite contrary to this broadly accepted thought, here we suggest that the time delays associated with large signal switching could show a universal behavior dictated by electronic dipoles, rather than ionic dipoles. Due to the resultant sudden and dramatic collapse of a contact layer depletion region, large signal switching delays are independent of ion mobilities. Furthermore, our detailed numerical simulations, supported by experimental results, indicate that terminal currents show a near steady state behavior well ahead of the relaxation of ionic distributions. These results have interesting implications toward the understanding and optimization of perovskite based electronic devices, including solar cells, LEDs, resistive memories, and ferroelectric memories.

Ionic Charge Imbalance in Perovskite Solar Cells

“…To explore hysteresis effects, time-dependent versions of the coupled Poisson and continuity equations are numerically solved (see details in section XI of Supporting Information). In accordance with the literature, here our results (Figure d) indicate that peak hysteresis occurs at a particular scan rate (i.e., for around 1 V/s for the set of parameters considered in simulations). We also observe that case (ii) has higher peak hysteresis (hysteresis index, HI = 0.33) than the other two cases (HI = 0.17 for case (i) and HI = 0.13 for case (iii)).…”

Intrinsic Degradation-Dependent Energy Yield Estimates for Perovskite/Silicon Tandem Solar Cells under Field Conditions

“…are also considered as per the literature. 6 experimental results are available in our prior publications [19][20][21]25 and in Sections A−D, Supporting Information.…”

“…Modeling strategy for perovskite solar cells under the influence of ion migration is well-established in prior literature − as well as our own previous publications. − Briefly, the J - V characterististics of the top cell are obtained through self-consistent numerical solution of the coupled Poisson and continuity equations, which describes the electrostatics and transport of charge carriers as well as ions, as listed below. .25ex2ex ∂ 2 ψ ∂ 2 x = prefix− q ε ( p − n + N I , p − N I , n ) ∂ p ∂ t = prefix− 1 q ∂ J normalp ∂ x − R normalp + G ∂ n ∂ t = 1 q ∂ J normaln ∂ x − R normaln + G ∂ N normalI , normaln ∂ t = 1 q ∂ J normalI …”

“…Table S2 of Supporting Information summarizes the functional dependence of such parameters. Details of the numerical simulation methodology including calibration with experimental results are available in our prior publications − , and in Sections A–D, Supporting Information.…”

“…Modeling strategy for perovskite solar cells under the influence of ion migration is well-established in prior literature − as well as our own previous publications. − Briefly, the J - V characterististics of the top cell are obtained through self-consistent numerical solution of the coupled Poisson and continuity equations, which describes the electrostatics and transport of charge carriers as well as ions, as listed below. …”