Towards Semi-Opaque Perovskite Solar Cells via Molecular Templates

Metal halide perovskite semi-transparent perovskite solar cells (ST-PSC) have drawn great interest for applications in building integrated photovoltaics (BIPV), such as solar windows.^.Conventionally, ST-PSC are realised by thinning the perovskite absorber layer to allow partial light transmission, while also replacing the opaque back electrode with one that is transparent. This approach has been shown to produce efficient and stable cells, with window-grade levels of transparency (>30%). However, their main drawback is the unavoidable perceived colour (typically red to yellow) due the optical bandgap laying within the visible range, which lowers the colour-rendering index (CRI) and therefore impedes their application in BIPV. A possible path to overcome this hurdle is by patterning the solar cell in a way that selected regions are entirely transmissive, while others remain fully absorbing. Such semi-opaque configurations can support greater efficiencies and color purity levels than ST-PSC. Towards this technological evolution, here, we explore a low-cost and efficient method for patterning metal-halide perovskites via stamping of a hydrophobic template on substrates. The facile approach is demonstrated to be scalable and suitable for both flexible and rigid substrates. It further removes the need for post-processing, thus minimizing potential lithographic steps, and the burden they pose. The use of such patterned perovskite films are considered within semi-opaque solar cell configurations, highlighting the challenges and the major opportunities that such patterned films and this form of solar cell architecture present.