Ionic-to-electronic current amplification in hybrid perovskite solar cells: ionically gated transistor-interface circuit model explains hysteresis and impedance of mixed conducting devices

Moia, Davide; Gelmetti, Ilario; Calado, Phil; Fisher, William D.; Stringer, Michael; Game, Onkar; Hu, Yinghong; Docampo, Pablo; Lidzey, David G.; Palomares, Emilio; Nelson, Jenny; Barnes, Piers R. F.

doi:10.1039/c8ee02362j

Cited by 158 publications

(223 citation statements)

References 37 publications

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“…The interpretation of the low frequency resistance is more controversial, due to complication arising from the coupling between ionic and electronic charge dynamics . However, the spectra are, as expected, more sensitive to the HSL composition.…”

Section: Resultsmentioning

confidence: 76%

From Bulk to Surface: Sodium Treatment Reduces Recombination at the Nickel Oxide/Perovskite Interface

Girolamo

Phung

Jost

et al. 2019

Adv Materials Inter

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The effect of sodium doping in NiO as a contact layer for perovskite solar cells is investigated. A combined X‐ray diffraction and X‐ray photoelectron spectroscopy analysis reveals that Na+ mostly segregates as NaOx/NaCl species around NiO crystallites, with the effect of reducing interface capacitance as revealed by impedance spectroscopy. Inspired by this finding, the NiO/perovskite interface in perovskite solar cells is modified via insertion of an ultrathin NaCl interlayer, which increases the NiO work‐function by 0.3 eV. This leads to an increase of power conversion efficiency, approaching 18%, and open‐circuit voltage due to a remarkable suppression of surface recombination, as revealed by photoluminescence analysis and light intensity–dependent electrical measurements.

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Section: Resultsmentioning

confidence: 76%

From Bulk to Surface: Sodium Treatment Reduces Recombination at the Nickel Oxide/Perovskite Interface

Girolamo

Phung

Jost

et al. 2019

Adv Materials Inter

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“…Furthermore, while the m–i–m device shows a reversal of the photocurrents at V ≤ V bi , after introducing charge‐selective CTLs (p–i–n) the photocurrent remains negative far into the forward‐bias well above V bi . It should be noted that ionic effects [ 20,26,27 ] have been neglected in these simulations.…”

Section: Resultsmentioning

confidence: 99%

On the Question of the Need for a Built‐In Potential in Perovskite Solar Cells

Sandberg

Kurpiers

Stolterfoht

et al. 2020

Adv Materials Inter

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charge generation over a wide and tunable range, [4] but also exhibit high carrier mobilities and long diffusion lengths up to several microns. [5][6][7] In any light harvesting device, appropriate contacts are critical to efficiently collect the photogenerated charges and deliver them to the external circuit. The contacts are responsible for providing the built-in asymmetry needed to create a driving force for the extraction of photogenerated carriers; [8] this built-in asymmetry can either be established by kinetic selectivity (diffusion-controlled) or by an energetic mismatch (drift-controlled) between the electrodes.The generic thin-film solar cell is composed of an active layer, sandwiched between a hole-extracting anode contact and an electron-extracting cathode contact. Under illumination, charge carriers generated within the active layer will drift-diffuse to the contacts and be extracted by the builtin asymmetry, resulting in the production of a net photocurrent. In organic solar cells, characterized by low carrier mobilities and short diffusion lengths, a strong built-in electric field across the active layer is necessary to enhance the charge extraction rate and avoid recombination. [9][10][11] This field is induced by the built-in potential V bi (or contact potential), originating from the work function difference between the anode and cathode and is largely unscreened due to the relatively low dielectric constants of organic semiconductors. Conversely, in perovskite solar cells, exhibiting carrier diffusion lengths of several microns, photogenerated charges should, in the absence of electric fields, be able to effortlessly traverse active layers of 200-500 nm without recombining. Subsequently, provided that kinetic selectivity at the contacts can be ensured, [12] the charge collection is expected to be diffusion controlled, [8,13] and a consensus is emerging along these lines. Kinetic selectivity is established by employing separate charge transport layers (CTLs) in-between the electrodes and the active layer, resulting in either an n-i-p or p-i-n type device architectures, with a hole transport layer (HTL, p-layer) at the anode and an electron transport layer (ETL, n-layer) at the cathode. In the ideal case, these layers are able to conduct majority carriers, while simultaneously preventing the extraction of minority carriers, thus creating a preferred direction for a diffusion-driven charge collection. Within this framework of charge extraction requirements, there is still some conjecture as to the exact role of the in-built potential and hence the precise nature of the driving force responsible for charge extraction.Perovskite semiconductors as the active materials in efficient solar cells exhibit free carrier diffusion lengths on the order of microns at low illumination fluxes and many hundreds of nanometers under 1 sun conditions. These lengthscales are significantly larger than typical junction thicknesses, and thus the carrier transport and charge collection should be expected to be diffusion ...

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“…Very recently, the large capacitance of PVSK solar cells under illumination has been proposed to originate from phase‐delayed transient current through devices, not a charge accumulation‐and‐release process. [ 35–37 ] Because it is relevant to resistive components rather than capacitive ones, the magnitude of the photoinduced capacitance is not limited. Pockett et al noted that a frequency‐dependent recombination process is potentially the origin of photoinduced capacitance in PVSK solar cells.…”

Section: Introductionmentioning

confidence: 99%

The Origin of Photoinduced Capacitance in Perovskite Solar Cells: Beyond Ionic‐to‐Electronic Current Amplification

Choi

Song

Han

et al. 2020

Adv Elect Materials

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Photoinduced capacitances of perovskite solar cells exhibit peculiarities such as an apparently high capacitance and an inductive feature, so‐called negative capacitance, which are not easily explained with typical carrier dynamics. Consequently, the origins of the photoinduced capacitances in perovskite solar cells have been intensively debated over the past several years. Here, the photoinduced capacitances of perovskite solar cells are analyzed by impedance spectroscopy. The analysis clarifies that the photoinduced capacitances of perovskite solar cells comprise several Debye relaxation‐type capacitance components. Among these components, the photoinduced capacitance in the low‐frequency range is attributed to ionic‐to‐electronic current amplification. However, the photoinduced capacitances in the middle‐ and high‐frequency ranges originate from bipolar injection. The clear elucidation of the origins of the photoinduced capacitances in perovskite solar cells provides comprehensive insights for analyzing properties of perovskites in either the time or frequency domain.

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Ionic-to-electronic current amplification in hybrid perovskite solar cells: ionically gated transistor-interface circuit model explains hysteresis and impedance of mixed conducting devices

Cited by 158 publications

References 37 publications

From Bulk to Surface: Sodium Treatment Reduces Recombination at the Nickel Oxide/Perovskite Interface

From Bulk to Surface: Sodium Treatment Reduces Recombination at the Nickel Oxide/Perovskite Interface

On the Question of the Need for a Built‐In Potential in Perovskite Solar Cells

The Origin of Photoinduced Capacitance in Perovskite Solar Cells: Beyond Ionic‐to‐Electronic Current Amplification

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