Effects of Annealing Temperature of Tin Oxide Electron Transport Layers on the Hysteresis of Perovskite Solar Cells
Alexander Hufnagel a, Meltem Aygüler a, Wolfram Jaegermann b, Michael Wussler b, Pablo Docampo c
a Technical University of Darmstadt, Jovanka-Bontschits-Straße, 2, Darmstadt, Germany
b University Newcastle, UK
Proceedings of Perovskite Thin Film Photovoltaics (ABXPV17)
València, Spain, 2017 March 1st - 2nd
Organizers: Henk Bolink and David Cahen
Oral, Meltem Aygüler, presentation 036
Publication date: 18th December 2016

An unexpected and impressive evolution in organic-inorganic perovskite solar cells (PSCs) with a vertical rise in power conversion efficiency (PCE) from 3.8% to 22.1% has energized the photovoltaic community to fabricate low-cost devices from this material with excellent optoelectronics properties. The highly efficient PSCs have been fabricated by using mesoporous TiO2 electron transport layers (ETLs), requiring annealing at high temperatures while mesoporous-free “planar” TiO2 ETL has suffered from a pronounced hysteresis. On the other hand, recent studies have shown the potential of low-temperature planar SnO2 ETLs in highly efficient PSCs with less hysteresis than planar TiO2. However, there is a lack of understanding of this improvement and detailed investigations of SnO2 layer and the interface between SnO2 and perovskite layers are needed.

Here, we fabricated PSCs using SnO2 prepared by atomic layer deposition (ALD) at low temperature as an ETL and triple cation and mixed halide perovskite as an absorber layer. The SnO2 layers were annealed at different temperatures in order to investigate if the hysteresis is resulting from the mismatch of energy levels of perovskite and SnO2 which can be changed by different annealing temperatures. Later, we have characterized the SnO2 layers with XRD and XPS, ensuring the formation of pure SnO2.  Moreover, our UPS measurements showed that the band alignment between perovskite absorber and SnO2 layer match quite well, resulting in less hysteresis.  Therefore, low-temperature SnO2 represents a significant contribution, offering a suitable energetics and improvements in series resistance at the ETL/perovskite interface on the way towards industrialization of PSCs.

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