Scaled Deposition of Ti₃C₂<i>T</i>_<i>x</i> MXene on Complex Surfaces: Application Assessment as Rear Electrodes for Silicon Heterojunction Solar Cells.

Abstract

Two-dimensional transition metal carbides (MXenes) are of great interest as electrode materials for a variety of applications, including solar cells, due to their tunable optoelectronic properties, high metallic conductivity, and attractive solution processability. However, thus far, MXene electrodes have only been exploited for lab-scale device applications. Here, to demonstrate the potential of MXene electrodes at an industry-relevant level, we implemented a scalable spray coating technique to deposit highly conductive (<i>ca</i>. 8000 S/cm, at a <i>ca</i>. 55 nm thickness) Ti₃C₂<i>T</i>_<i>x</i> films (<i>T</i>_<i>x</i>: surface functional groups, <i>i</i>.<i>e</i>., -OH, -O, -F) <i>via</i> an automated spray system. We employed these Ti₃C₂<i>T</i>_<i>x</i> films as rear electrodes for silicon heterojunction solar cells as a proof of concept. The spray-deposited MXene flakes have formed a conformal coating on top of the indium tin oxide (ITO)-coated random pyramidal textured silicon wafers, leading to >20% power conversion efficiency (PCE) over both medium-sized (4.2 cm²) and large (243 cm², <i>i</i>.<i>e</i>., industry-sized 6 in. pseudosquare wafers) cell areas. Notably, the Ti₃C₂<i>T</i>_<i>x</i>-rear-contacted devices have retained around 99% of their initial PCE for more than 600 days of ambient air storage. Their performance is comparable with state-of-the-art solar cells contacted with sputtered silver electrodes. Our findings demonstrate the high-throughput potential of spray-coated MXene-based electrodes for solar cells in addition to a wider variety of electronic device applications.