Revealing Defective Interfaces in Perovskite Solar Cells from Highly Sensitive Sub-bandgap Photocurrent Spectroscopy Using Optical Cavities
Bas van Gorkom a, Tom van der Pol a, Kunal Datta a, Martijn Wienk a, René Janssen a
a Molecular Materials and Nanosystems, Institute for Complex Molecular Systems, Eindhoven University of Technology, The Netherlands
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Oral, Bas van Gorkom, presentation 127
Publication date: 20th April 2022

Defects in perovskite solar cells are known to affect the performance, but their precise location and role remain to be firmly established. Given their nature, the detection of defect states requires highly sensitive characterization techniques. Here, we present highly sensitive measurements of the sub-bandgap external quantum efficiency to investigate defect states in perovskite solar cells. From the sub-bandgap photocurrent spectra, at least two defect states can be identified in p-i-n solar cells.

As absorption below the band gap is negligible, the measured spectra are prone to significant interference effects. These effects make it difficult to derive energetic parameters for the defect states. By comparing devices with opaque and semi-transparent back contacts, we demonstrate the large effect of optical interference on the magnitude and peak position in the sub-bandgap EQE in perovskite solar cells. From optical simulations of the electric field intensity, it is revealed that defects localized near the interfaces are responsible for the measured photocurrents.

A series of optical cavities, using optical spacers of different lengths and a mirror on top of semi-transparent devices, is then constructed. This allows for the precise manipulation of the optical interference without affecting the electrical properties of the device. By comparing experimental and simulated EQE spectra, we show that defects contributing to sub-bandgap EQE in p-i-n devices are predominantly located near the interface between the perovskite layer and the electron transport layer.

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