Understanding the physical response of perovskite solar cells by frequency domain and time transient decay methods
Juan Bisquert a
a Universitat Jaume I, Institute of Advanced Materials (INAM) - Spain, Avinguda de Vicent Sos Baynat, Castelló de la Plana, Spain
nanoGe Perovskite Conferences
Proceedings of International Conference on Perovskite Thin Film Photovoltaics and Perovskite Photonics and Optoelectronics (NIPHO20)
Sevilla, Spain, 2020 February 23rd - 25th
Organizer: Hernán Míguez
Invited Speaker, Juan Bisquert, presentation 070
Publication date: 25th November 2019

The dynamic response of metal halide perovskite devices shows a variety of physical responses that need to be understood and classified for enhancing the performance and stability and for identifying new physical behaviours that may lead to developing new applications. These responses are the outcome of complex interactions of electronic and ionic carriers in the bulk and at interfaces. Based on a systematic application of frequency modulated techniques and time transient techniques to the analysis of kinetic phenomena, we present a picture of the dominant effects governing the kinetic behaviour of halide perovskite devices. First with impedance spectroscopy we provide an interpretation of capacitances as a function of frequency both in dark and under light, and we discuss the meaning of resistances and how they are primarily related to the operation of contacts in many cases. The capacitance reveals a very large charge accumulation at the electron contact, which has a great impact in the cell measurements, both in photovoltage decays, recombination, and hysteresis. We also show the identification of the impedance of ionic diffusion by measuring single crystal samples. Working in samples with lateral contacts, we can identify the effect of ionic drift on changes of photoluminescence, by the creation of recombination centers in defects of the structure.1 We also address new methods of characterization of the optical response by means of light modulated spectroscopy. The IMPS is able to provide important influence on the measured photocurrent.2 We describe important insights to the measurement of EQE in frequency modulated conditions, which shows that the quantum efficiency can be variable at very low frequencies. The combination of IMPS and Impedance Spectroscopy is able to provide a detailed picture that explains low frequency characteristics, influencing the fill factor of the solar cell. As a summary we suggest an interpretation of the effects of charge accumulation, transport, and recombination. on current-voltage characteristics and time transient properties, and we suggest a classification of the time scales for ionic/electronic phenomena in the perovskite solar cells.

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