Room temperature atomic layer deposition of Al2O3 and replication of butterfly wings for photovoltaic application

In this paper, we present two key process steps for potential applications in the fabrication of low-cost and high-efficiency ultrathin monocrystalline silicon (mono-Si) solar cells to effectively harvest solar energy. One is to grow an Al2O3 passivation layer on the rear side of an Si wafer by a successive atomic layer deposition (ALD) at room temperature (25 °C). The other is to produce a bio-inspired antireflection structure on the front side of the Si wafer by replicating butterfly wing patterns. The capacitance–voltage measurements reveal that the successive ALD procedure can yield a higher negative charge density at the Al2O3/Si interface relative to the conventional one. The measurement results of quasi-steady-state photoconductance indicate that after annealing, the 25 °C ALD Al2O3 layers reach a similar passivation level to the p-type Si wafers compared to that deposited at 250 °C. With the help of an ALD Al2O3 layer, butterfly wing patterns (Hypochrysops polycletus) are replicated on a PMMA layer which is on an SiO2/Si stack. This work demonstrates the ability for replicating the natural photonic features on Si wafers and other substrates by using nanoimprint.