SENECA Talk 5: Using transient methods to characterize recombination and extraction in halide perovskite solar cells

EventLectures

Welcome at the SENECA Talks, a monthly seminar series on Solar ENErgy Conversion and storAge organised by EnergyVille/imec/UHasselt (imo-imomec).

July 8th 2024 11:00 a.m.
Onsite EnergyVille 2 (Thor Park 8320, 3600 Genk) and online via MS Teams
Contact: Sudhanshu Shukla – Sudhanshu.Shukla@imec.be

This lecture will be held in English.

The efficiency of halide perovskite solar cells has been continuously rising over the past decade to values above 26%. Future technological development will have to deal with issues of device stability but also thrive to further minimize efficiency-limiting loss processes in the bulk and at interfaces within the cell stack. The identification and understanding of electrical losses will require the ability to characterize solar cells and multilayer stacks with a variety of steady-state, time-domain and frequency-domain techniques that are sensitive to the transport and recombination of charge carriers. Especially, time- and frequency-domain techniques offer a large amount of information on dynamic processes in the solar cell, while posing a substantial challenge in terms of the complexity of data analysis.

Here, we discuss three novel and relevant aspects related to transient photoluminescence (TPL) and photovoltage spectroscopy (TPV) applied to halide perovskites. We show that by using extremely low repetition rates and a gated CCD camera, we can obtain high dynamic range TPL data with continuously changing decay times that exceed 100µs. Furthermore, we show that by changing the repetition rate, basically any decay time can be extracted from one sample, whereby the extracted decay time is approximately the inverse repetition rate. We explain why this is the case both mathematically and physically. Whenever, higher order recombination due to e.g. band to band or band to shallow trap transitions affects the decay, the decay time will correlate with the time range of the measurement which is typically limited by the inverse repetition rate. Finally, we show how to separate recombination from extraction by using TPV data combined with a novel analysis approach based on the determination of eigenvalues of a 2 × 2 matrix. The model provides two time constants (the inverse eigenvalues), one for the rise and one for the decay of the voltage after the pulse. These two time constants can be experimentally determined as a function of light intensity. By comparison of model and experimental data, we can then derive a time constant for recombination and one for charge extraction, whereby the ratio of these two time constants is directly correlating with solar cell efficiency.

About the speaker

Thomas Kirchartz is currently a professor of electrical engineering and information technology at the University Duisburg-Essen and the head of the department of Analytics and Simulation and the group of Organic and Hybrid Solar Cells at the Research Centre Jülich (Institute for Energy and Climate Research). Previously he was a Junior Research Fellow at Imperial College London. His research interests include all aspects regarding the fundamental understanding of photovoltaic devices including their characterization and simulation.

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