Invited Paper TF-MoA1
Atomic Layer Deposition for Organic and Perovskite Solar Cells

Monday, October 22, 2018, 1:20 pm, Room 104B

Organic and perovskite based solar cells (OSCs / PSCs) provide an intriguing avenue for next-generation thin-film photovoltaics. Aside from the photo-active material, the choice of charge extraction layers (CELs) substantially impacts performance and lifetime. For OSCs, the use of ALD-grown tin-oxide (SnO_x) as electron extraction layer (EEL) mitigates two critical issues, i.e. light soaking^[1] and photo-shunting^[2], which frequently occur in case ZnO based EELs are used. In tandem OSCs, all-oxide recombination interconnects based on high work-function (WF) MoO_x and low-WF ALD grown SnO_x show ideal alignment of the conduction band of MoO_x and SnO_x and loss-free addition of the open circuit voltages of the two sub-cells.^[3]

In the second part, I will show ALD-grown SnO_x as impermeable EEL for PSCs to enable impressive stability of the cell against heat and moisture. The SnO_x is positioned between the metal electrode and the perovskite. Its outstanding permeation barrier properties^[4] protect the MAPbI₃ against the ingress of moisture or migrating metal atoms, while simultaneously the metal electrode is protected against leaking halide compounds. Thereby, PSCs with an efficiency of >20% and outstanding long-term stability can be achieved. They remain stable over 4500 hours at elevated temperatures as well as in ambient air. ^[5,6] ALD-grown SnO_x is also excellently suited to sandwich and protect ultra-thin metal layers (Ag or Cu) as cost efficient Indium-free semitransparent electrodes (SnO_x/metal/SnO_x) in PSCs. Using photoelectron spectroscopy, we unravel the formation of a PbI₂ interfacial layer between a SnO_x EEL and the perovskite. The resulting interface dipole between SnO_x and the PbI₂ depends on the choice of oxidant for ALD (water, ozone, oxygen plasma). SnO_x grown by using ozone affords hysteresis-free devices with a stable efficiency of 16.3% and a very high open circuit voltage of 1.17 V.^[7] Ultimately, SnO_x grown by spatial-ALD at atmospheric pressure is presented. Its suitability to replace its low pressure analogues in PSCs is shown. ^{[1, 2]} This work paves the way towards roll-to-roll fabrication of stable, Indium-free PSCs.

[1] S. Trost et al., Adv. Energy Mater.2015, 5, 1500277.

[2] S. Trost et al., Adv. Energy Mater.2016, 6, 1600347.

[3] T. Becker et al., Adv. Energy Mater.2018, 8, 1702533.

[4] A. Behrendt et al., Adv. Mater.2015, 27, 5961.

[5] K. O. Brinkmann et al., Nat. Comms.2017, 8, 13938.

[6] J. Zhao et al., Adv. Energy Mater.2017, 7, 1602599.

[7] T. Hu et al., Adv. Mater.2017, 29, 1606656.

[8] L. Hoffmann et al., J. Vac. Sci. & Technol. A2018, 36, 01A112.

[9] L. Hoffmann et al., ACS Appl. Mater. & Interf.2018, 10, 6006.