Patterning of transparent polymers using high-throughput methods: Application in flexible perovskite solar cells with enhanced light trapping
Perovskite solar cells (PSC) are a promising low-cost energy source for niche markets, such as energy harvesting semitransparent windows, and colored or arbitrary shaped solar modules for portable power sources or building facades. Furthermore, the possibility to fabricate flexible solar modules allows the integration of the whole manufacturing process into a roll-to-roll facility with the potential of reducing dramatically the fabrication costs. In the quest for high efficiency flexible PSC, the absorbed sunlight can be maximized employing a light trapping technique, such as using a microstructured substrate capable to scatter or diffract the incoming light into multiple directions elongating the optical path in the absorber. This work presents a new strategy to pattern microstructures on polymers suitable as transparent substrates for flexible PSC with enhanced light trapping. This industrial compatible approach consists only on two processing steps. First, a cylindrical metallic stamp is structured using Direct Laser Interference Patterning (DLIP), and next, the stamp is used in a roll-to-roll hot embossing system to transfer the stamp pattern to polymeric foils. Optimizing the DLIP processing and hot embossing parameters, high-quality imprints were obtained with periodic features with a spatial period of 2.7 mm. PSC were deposited onto these structured substrates showing an increase in the light absorption and efficiency. Spectroscopic characterization using an integrating sphere suggests that the PSC efficiency increase is caused by an elongated optical path inside the perovskite due to scattering and diffraction in the visible spectrum.