Aqueous dispersions of silver nanowires state an environmentally friendly avenue for highly conductive, yet transparent top electrodes for semi-transparent perovskite solar cells. However, for the well-known chemical instability of halide perovskites upon exposure to water, there are no reports of successful aqueous processing on top of perovskite devices. Here, we show that electron extraction layers of AZO/SnOx [1,2], with the SnOx grown by low temperature atomic layer deposition, provide outstanding protection layers, which even afford the spray coating of AgNW electrodes (sheet resistance Rsh =15 Ohm/sq and a transmittance of 90%) from water-based dispersions without damage to the perovskite.
The layer sequence of the inverted cells is ITO/PTAA/perovskite/PCBM/AZO/SnOx/top-electrode. In devices without the ALD SnOx, aqueous spray processing decomposes the perovskite layers. Interestingly, the direct interface of Ag-NW/SnOx comprises a Schottky barrier, with characteristics strongly dependent on the charge carrier density of the SnOx. For a carrier density below 10^18 cm^-3, S-shaped J-V characteristics are found, that successively vanish upon UV-light soaking. For our low-T SnOx with 10^16 cm^-3, the insertion of a thin interfacial layer with a high charge carrier density (10^20 cm^-3), e.g. 10nm of ITO, is found to afford high performance semitransparent PSCs with an efficiency of 15%. Most importantly, compared to ITO electrodes Ag-NW based electrodes provide a key to achieve a higher transmittance in the IR, which is desirable for tandem Si/PSCs.
 K. Brinkmann et al., Nat. Commun. 8, 13938 (2017).
 L. Hoffmann et al. ACS Applied Mater. & Interfaces 10, 6006 (2018).