The device physics of metal halide perovskite interfaces, part 2: equivalent circuit model
Davide Moia a b, Ilario Gelmetti c d, Phil Calado a, William Fisher a, Michael Stringer e, Onkar Game e, Yinghong Hu f, Pablo Docampo f g, David Lidzey e, Emilio Palomares c h, Joachim Maier b, Jenny Nelson a, Piers Barnes a
a Department of Physics, Imperial College London, UK
b Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569, Stuttgart
c Institute of Chemical Research of Catalonia (ICIQ), Barcelona Institute of Science and Technology (BIST), Avinguda dels Països Catalans, 16, Tarragona, Spain
d Departament d’Enginyeria Electrònica, Elèctrica i Automàtica, Universitat Rovira i Virgili, Avinguda dels Països Catalans, 26, Tarragona, Spain
e Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
f Department of Chemistry and Center for NanoScience (CeNS), LMU München, Butenandtstrasse 5-13, 81377 München, Germany
g Physics Department, School of Electrical and Electronic Engineering, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
h ICREA – Institució Catalana de Recerça i Estudis Avançats, Passeig de Lluís Companys, 23, Barcelona, Spain
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Davide Moia, 135
Publication date: 11th February 2019

Our recent drift-diffusion simulations indicate that the electrostatic potential arising from mobile ion redistribution controls electronic charge transfer processes such as recombination in mixed conducting lead halide perovskite devices and can give rise to apparent capacitive behavior.[1] The capacitive features of a mixed conductor are traditionally described within equivalent circuit models by a chemical capacitance, which accounts for bulk polarization effects.[2,3] and scales with the thickness of the device, complemented by an interfacial capacitance, related to electronic and ionic accumulation at the interfaces with the contacts. Since the effect described is not simply associated with an accumulation or depletion of charges in the active layer, it cannot be adequately described with a conventional capacitor. We identify the bipolar transistor as a most appropriate circuit element to reproduce analytically the observation of ionically-gated electron transfer at interfaces and include it into an equivalent circuit model that accounts for and couples ionic and electronic carrier dynamics.[1] We propose that the huge capacitive and/or inductive behavior[4] observed for thin film perovskite solar cells is best described by electronic currents that are in fact an amplified version of the ionic current flowing in the bulk of the active layer. The resulting model yields good fits to the experimental impedance spectra as a function of applied voltage bias and light intensity, and can reproduce large perturbation transient measurements such as hysteretic current-voltage characteristics.[5] It also enables to evaluate parameters such as the ionic conductivity of the hybrid perovskite, the observed ideality factor of the device and the properties of the space charge within the active layer and in the contact regions. The limits under which the present model coincides with the traditional picture are discussed.

We thank the EPSRC for funding this work (EP/J002305/1, EP/M025020/1, EP/M014797/1, EP/L016702/1, EP/R020590/1). I.G. and E.P. would like to thank the MINECO for the CTQ2016-80042-R project. E.P. also acknowledges AGAUR for the SGR project 2014 SGR 763 and ICREA for financial support.

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