Creation of a Solution Processed Scalable Transparent Top Electrode for Application in Perovskite Solar Cells

Perovskite solar cells frequently rely on a transparent substrate with a non-scalable thermally evaporated TCO for the transmission of photons to the active layers, however, when perovskites are used on an opaque substrate or for semi-transparent applications the top electrodes, which play a critical role in the performance of a solar cell, must instead be transparent to allow photons to reach the active layer, with semi-transparent solar cells too allowing photon to reach the active layers from both sides.<br/>This work presents how single walled carbon nanotubes (SWCNTs) and silver nanowires (AgNWs) can be used in combination to create a low temperature solution processable transparent top electrode for use in opaque substrate-based and semi-transparent perovskite solar cells.<br/>Using a hybrid electrode consisting of low-cost, commercially available inks to create a carbon nanotube in a silver nanowire matrix provides a scalable solution for creating an electrode compatible with roll-to-roll lines. This was achieved through experiments optimising the ratio between the CNT and AgNW solutions using UV-Vis-NIR to measure the transparency and 4-point probe to measure the sheet resistance and repeated over various thicknesses which was further investigated through AFM. The use of opaque substrates, like steel, and the application of a solar cell coated directly onto it provides an additional function outside of their structural uses, giving existing materials the ability to generate electricity utilizing their surface area for energy generation.<br/>This solution processed electrode can be deposited through both spray and slot die coating techniques. The hybrid electrode layer provides improved adhesion over a film of AgNWs alone with the interaction between the CNTs and AgNWs creating a more stable layer reducing the movement of silver ions towards the perovskite. The network of intermeshed nanomaterials creates a high conductivity of charge with the spaces between them creating a small variance in the percentage transmission of wavelength across the visible spectrum.<br/>Using this electrode, we were successfully able to create working perovskite solar cells using both sprayed and slot die deposition with devices performing the same when measure either through a transparent substrate, as in traditional devices, or through the top electrode.